Highly Phosphorescent Cyclometalated Iridium(III) Complexes for

Subscriber access provided by University of Cincinnati Libraries

Article

Highly Phosphorescent Cyclometalated Iridium (III) Complexes for Optoelectronic Applications - Fine Tuning of the Emission Wavelength through Ancillary Ligands Lukasz Skorka, Michal Filapek, Lidia Zur, Jan Grzegorz Malecki, Wojciech Pisarski, Marian Olejnik, Witold Danikiewicz, and Stanis#aw Krompiec J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b01663 • Publication Date (Web): 20 Mar 2016 Downloaded from http://pubs.acs.org on March 21, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Highly Phosphorescent Cyclometalated Iridium(III) Complexes for Optoelectronic Applications - Fine Tuning of the Emission Wavelength Through Ancillary Ligands Łukasz Skórka†,*, Michał Filapek‡, Lidia Zur‡, Jan Grzegorz Małecki‡, Wojciech Pisarski‡, Marian Olejnik§, Witold Danikiewicz§ and Stanisław Krompiec‡ †

Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland. E-mail: [email protected] ‡

§

Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.

Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.

1 Environment ACS Paragon Plus


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 43

ABSTRACT: A series of novel, highly phosphorescent cyclometalated iridium(III) complexes of type

[(X2C^N)2Ir(Q2bpy)]+PF6-

(where

X2C^N

is

2-phenylpyridine

or

2-(2,4-difluorophenyl)pyridine anion and Q2bpy are 4,4'-bifunctionalized 2,2’-bipyridines) is presented. The complexes were fully characterized by means of NMR spectroscopy, high resolution mass spectrometry (HRMS), cyclic voltammetry

and

UV-Vis. For several

compounds also the crystallographic structures were obtained. The cyclometalates exhibited efficient photoluminescence at 298 K both in solution and in solid state with good intensity and color purity. The emission wavelength range covered almost the whole visible spectrum and was strongly correlated with the EWG/ERG character of the Q substituent in the ancillary ligand. For further insight into the electronic structure of the complexes, a comprehensive electrochemical support (CV) was introduced and finally it was confronted with theoretical background using density functional theory approach together with time-dependent calculations of the excited states.

INTRODUCTION: A vast majority of modern technologies continuously stimulates the extensive growth in the search for novel materials that would exhibit outstanding and unique properties.1,2 A wide range of such materials covers species capable of emitting light, that may be utilized as dopants for organic light-emitting devices (OLED)3-22 or light-emitting electrochemical cells (LEC).23-29 Cyclometalated iridium(III) complexes, which are a part of that group, have attracted a constantly growing attention throughout recent years due to their easy preparation and valuable photoluminescence properties. They were found to possess an extreme potential in the field of organic electronics since the very first attempts of their synthesis and physicochemical characterization.30 They are also investigated in various physicochemical


Page 3 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


domains like electron transfer,

31-33

non-linear optical properties34-35 and are even utilized as

ligands for a variety of metal nanoparticles.36 The key feature that allows the broad utilization of Ir cyclometalates is their strong and bright phosphorescence, lifetimes of the excited states within the microsecond range and a high ability to tune the emission wavelength.37-41 Also the variety of structures enables to choose from diverse cationic,26,42-48 neutral49-55 and anionic56,57 species depending on the situation. The incorporation of cyclometalating ligand (carrying a substantial ligand-field strength) combined with the efficient spin-orbit coupling of the iridium metal center enhances efficient intersystem crossing from singlet excited stated to the triplet manifold, which results in effective luminescence and excellent quantum yields.39,58 Throughout recent years there has been a huge progress in the field of cationic iridium cyclometalates, aimed especially at their design and structure-property relationships. The research based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) constitutes a great importance, because it allows estimations of the key features of the designed compound prior to the synthesis in order to predict the desired properties.39,46,59-73 The theoretical assistance also gives the important clues for the proper interpretation of UV-Vis60,61 and emission spectra59,61,67 as well as allows to correlate the electrochemical reactions with particular parts of the molecules.74 Even more interesting is the recent use of relativistic approximations for better description of spin-orbit coupling.75-79 For a comprehensive study also the effects associated with the solvation of the isolated molecules, must also be taken into account. The tuning of the emission wavelength is strongly correlated with adjusting the HOMOLUMO gap within the complex.5,25,26,39,42 Stabilization of HOMO42,80 and destabilization of LUMO26,42 provides with direct enhancement of the emission energy and shifting it towards the



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

blue region.56,57 The opposite leads to a red-shift of the emission81,82 or may in the end enhance a non-radiative decay through vibrational deactivation.83,84 Within the cationic iridium cyclometalates various ways to tune the aforementioned properties were made. First, the extension of the aromatic π-conjugation of either cyclometalating81,85 or ancillary25,82,86 ligand decreases the HOMO-LUMO gap and shifts the emission bathochromically. Another approach allows to use the simultaneous functionalization of the C^N and ancillary ligands in two opposite directions. The incorporation of withdrawing fluorine substituents in the phenyl ring of the cyclometalating phenylpyridine stabilizes HOMO42 (associated with the Ir and phenyl ring). Sometimes even the cis/trans relationships in the coordination sphere of iridium can significantly alter the emission color.87 However, according to recent study the use of fluorine as a means of HOMO adjuster needs to be thought over thoroughly.88,89 As explained by Bolink and Frey90 and co-workers species consisting of more than two fluorines tend to decompose during operation of the corresponding device (OLED or LEC), which disturbs the color fine-tuning and the affects the overall performance. Nazeeruddin and De Angelis achieved the destabilization of LUMO through the substitution of the 4,4’ positions in the 2,2'-bipyridine ligand with strongly electrondonating dimethylamino groups, which yielded either green26 or green-blue42 phosphorescence. For the systems consisting of cyclometalating 2-phenylpyridine and bipyridine ancillary ligand there was almost no further study reaching beyond strongly electron-releasing groups with only small exceptions.91-93 There are therefore continued attempts to functionalize the iridium(III) cyclometalates in such a way to obtain various emission colors, most preferably covering the blue region.5,28,94-97 Herein, we present a comprehensive research on the structure-property relationships in a series of cyclometalated Ir(III) complexes consisting of either 2-phenylpyridine or 2-(2,4-


Page 4 of 43

Page 5 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


difluorophenyl)pyridine and one of the 4,4’-disubstituted 2,2’-bipyridine derivatives. As substituents we used amino, methoxy, fluoro and cyano groups ranging from higly electronreleasing to highly electron-withdrawing character.

EXPERIMENTAL SECTION: Details concerning chemical supply, synthesis, spectroscopy, photophysical measurements, X-ray crystallography, electrochemistry and DFT calculations were moved to Supporting Information.

RESULTS AND DISCUSSION 1. Synthesis and characterization of cationic iridium(III) cyclometalates The synthetic route towards ancillary ligands and the corresponding iridium(III) cyclometalated complexes is presented in Scheme S1. All ligands but one were synthesized from a common source - 4,4'-dinitro-2,2'-bipyridine 1,1'-dioxide according to presented procedures with yields between 60 - 99%. 4,4'-difluoro-2,2'-bipyridine was synthesized for the first time in a homo-coupling reaction of the Stille type of 2-bromo-4-fluoropyridine (40% yield). Iridium(III) cyclometalates were obtained in a typical two step reaction, where iridium trichloride was first refluxed

with

2.5

eq.

of

cyclometalating

ligand

(2-phenylpyridine

or

2-(2,4-

difluorophenyl)pyridine - C^N-H) in 2-ethoxyethanol/water solution. Then the corresponding µchloro-bridged dimers were then reacted with 2.5 eq. of the ancillary ligand followed by subsequent counter ion exchange for hexafluorophosphate. Chemical structures of the target cyclometalates are depicted in Table 1.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 43

Table 1. Chemical structures of the Ir(III) complexes under investigation in this paper. X

Q

Abbreviation

Number

H

NH2

[Ir(ppy)2(44dabpy)]PF6

1

F

NH2

[Ir(24dfppy)2(44dabpy)]PF6

2

[Ir(ppy)2(44dmbpy)]PF6

3

H OMe F

OMe [Ir(24dfppy)2(44dmbpy)]PF6

4

H

F

[Ir(ppy)2(44dfbpy)]PF6

5

F

F

[Ir(24dfppy)2(44dfbpy)]PF6

6

H

CN

[Ir(ppy)2(44dcbpy)]PF6

7

F

CN

[Ir(24dfppy)2(44dcbpy)]PF6

8

All presented compounds were characterized by a series of NMR experiments (1H, 13C, COSY, HMQC, HMBC - wherever necessary), HRMS and moreover for [Ir(ppy)2(44dmbpy)]PF6 (3), [Ir(ppy)2(44dcbpy)]PF6 (7) and [Ir(24dfppy)2(44dfbpy)]PF6 (6) by X-Ray diffraction on single crystals. In the case of [Ir(24dfppy)2(44dcbpy)]PF6 (8) the cyano groups hydrolyzed before crystal growth in methanol solution to obtain the corresponding dimethyl ester - 8*.


Page 7 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. Molecular structures of 3, 6, 7, 8* complexes with thermal ellipsoids at 50% probability level. Hydrogens, solvents and PF6- ions are omitted for clarity. Details concerning crystal structure are presented in Table S1 (ESI) with respective ORTEP drawings depicted in Figure 1. In each case the cyclometalating ligands are bonded to iridium metal center with nitrogen atoms being in trans disposition, which is common for this class of compounds.12,18,27,28,37-43,81-83,86,87,94,95,97



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2. UV-Vis Study The UV-Vis spectra of complexes 1-8, measured in dichloromethane solutions, are presented in Figure 2 where fluorinated and non-fluorinated (ppy and 24dfppy) cyclometalates are separated into two groups for clarity. In each case the intense, high-energy band is usually considered as originating from π-π* transitions, while the less intense, red-shifted band is attributed to MLCT. Their peak maxima are listed in Table 2 together with the corresponding molar extinction coefficients. The relative positions of the aforementioned bands remain almost constant with the tolerance of a few nanometers for both π-π* and MLCT. The trend of the π-π* band for 1, 2, 3, 4, 5 and 6 is almost the same with peak maxima at 260 nm, 255 nm, 258 nm, 251 nm, 257 and 250 nm, respectively. For 7 and 8, however these bands are resolved as two with maxima at 250 nm, 303 nm for 7 and 237 nm and 312 nm for 8. The intensities of the π-π* transitions gradually drop in both sets of cyclometalating ligands when moving from strongly electron donating 4,4’-diamino-2,2’-bipyridine to electron accepting 4,4’-dicyano-2,2’bipyridine which is further visualized in the ε drop at peak maximum (Table 2). On the other hand the behavior of the MLCT band is quite opposite. Electron accepting ligands (44dcbpy) cause the intensity to rise when at the same time for 44dabpy the MLCT remains on the shoulder of π-π* (the case of 2). The nature of UV-Vis transitions was analyzed on the basis of TD-DFT calculations applying the level of theory specified in the experimental section and moreover with the aid of natural transition orbitals (NTOs - see Supporting Information Tables S2 - S9).


Page 8 of 43

Page 9 of 43

-1 -1 Molar Extinction Coefficient (M *cm )

80000 70000 1 3 5 7

60000 50000 40000 30000 20000 10000 0 250

300

350

400

450

500

550

600

650

700

Wavelength (nm)

80000 -1 -1 Molar Extinction Coefficient (M *cm )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


70000 2 4 6 8

60000 50000 40000 30000 20000 10000 0 250

300

350

400

450

500

550

600

650

700

Wavelength (nm)

Figure 2. UV-Vis spectra of complexes 1-8. It should be pointed out that according to theoretical results most of the transitions are spinallowed singlet - singlet excitations, however in many cases there may be also a contribution



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 43

from spin-forbidden singlet - triplet transitions. Nevertheless, the effect of spin-orbit coupling was not accounted for in the TD-DFT calculations and therefore the intensities of singlet-triplet transitions cannot be thoroughly analyzed. The separate and normalized UV-Vis spectra along with TD-DFT oscillator strengths are attached in the Supporting Information (Figures S35 S42). First, it must be noted that according to TD-DFT in all eight cases the HOMO – LUMO excitation is not allowed which is evidenced by the oscillator strengths equal zero (Table 2).

Table 2. Photophysical data on absorption and luminescence of complexes 1-8. Compo und

λabsa (nm)

εb

λexc (nm)

λem (nm)

Quantu m yieldc

τd (µs)

k re

knrf

λabsg (nm)

Major Contribution

1

260

6.2

350

518

0.40

4.6

0.87

1.30

432.63

HOMO → LUMO (99%)

347

0.9

387

0.5

255

6.6

350

456

0.56

4.6

1.22

0.96

395.86

HOMO → LUMO (97%)

2

484 3

4

5

6

7

239

4.6

258

7.0

339

1.2

251

6.4

360

0.7

257

5.6

267

5.6

379

0.8

250

4.9

360

0.7

251

4.1

303

4.1

350

565

0.09

4.5

0.20

2.02

481.58

HOMO → LUMO (99%)

360

507

0.54

4.6

1.17

1.00

437.28

HOMO → LUMO (99%)

360

606

0.01

4.8

0.21

2.06

525.20

HOMO → LUMO (99%)

360

538

0.25

4.8

0.52

1.56

473.49

HOMO → LUMO (99%)

390

608

0.01

not register ed

-

-

667.47

HOMO → LUMO (99%)

651


Page 11 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


8

372

1.1

237

3.6

312

2.1

364

0.8

370

598

0.11

4.7

0.23

1.89

586.74

HOMO → LUMO (99%)

All measurements were carried out in dichloromethane solution. a extracted from first derivative, b [ε] = 104 M-1*cm-1, c +/-5% based on estimation of photoluminescene intensity/absorbance ratio for sample and standard dλexc = 350 nm, e radiative decay rate kr = ϕ/τ [kr] = 105 s-1 f non-radiative decay rate knr = (1-ϕ)/τ [knr] = 105 s-1 g HOMO → LUMO transition calculated via TD-DFT

Moreover, in the calculated wavelengths the exchange of the ancillary ligand to more electronaccepting (jump from -NH2 to -CN) causes gradual red-shift in both series of cyclometalates (with ppy and 24dfppy). On the other hand, by comparing complexes with the same ancillary ligand one can easily find that attaching fluorines on ppy side results in the blue-shift of the HOMO – LUMO transition in each pair. These observations will be also reflected in other photophysical and electrochemical properties directly connected with modulation of the Eg value. The spread of the energy of the first excited state is also huge covering the whole visible part of the spectrum from 395.86 nm for 2 to 667.47 nm for 7. Since HOMO - LUMO excitation does not bring any contribution the electronic spectrum, the observed bands come from different transitions, which involve other orbitals. According to NTO, the lowest energy MLCT band for each complex is raised from a mixture of two transitions, namely: Ir(d) → bpy and Ir(d) → ppy. For compounds 1-6 Ir(d) → ppy was found to be of lower energy, while for 7 and 8 the situation is inverted. For the π-π* bands even with the aid of NTOs the image becomes multiconfigurational anyway. However, it is still possible to attribute the transitions to intraligand charge transfers (ppy → ppy and bpy → bpy) and some interligand charge transfers



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 43

(ppy → bpy and bpy → ppy). To be more precise it should be also noted that there is also some MLCT contribution in the aforementioned excitations as evidenced by NTO. 3. Photoluminescence A simple chemical variation of ligands brings a huge opportunity of tuning both the emission wavelength and intensity. The respective photoluminescence spectra of complexes 1-8 are presented in Figure 3 (with data included in Table 2). As expected, the choice of substituents allows to modulate the color of the emission. As a result there is one true-blue emitter with 4,4'diamino-2,2'-bipyridine on the ancillary and fluorinated 2-phenylpyridine on the cyclometalating site (Table 2 entry 2). Then, the green emission was observed in the case of 1 and 4 with maxima at 518 nm and 507 nm, respectively. The remaining compounds emit in the yellow (compounds 3 and 6) and red (5, 7 and 8) regime. What is crucial in the luminescence study is that the emission intensity measured as quantum yield is also significantly affected by the ligand design. It varies from 0.56 (2) and 0.54 (4) to 0.01 for 5 and 7. In general, huge quantum yield is observed, when strongly electron-donating ancillary ligands are combined with fluorinated 2-phenylpyridine. The features affecting this phenomenon are described below in DFT section.


Page 13 of 43

Normalized Intensity (a.u.)

1,0 1 3 5 7

0,8

0,6

0,4

0,2

0,0 400

450

500

550

600

650

700

750

800

850

Wavelength (nm)

1,0

Normalized Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2 4 6 8

0,8

0,6

0,4

0,2

0,0 400

450

500

550

600

650

700

750

800

850

Wavelength (nm)

Figure 3. Normalized PL spectra of complexes 1-8 measured in degassed dichloromethane solution. Based on luminescence decay curves recorded for iridium complexes, luminescence lifetimes were determined. Their values are given in Table 2. The observed lifetimes are consistent with emission from a triplet state. Luminescence decays for examined compounds are nearly exponential and their measured lifetimes change very slightly from 4.6 µs to 4.9 µs (for details



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 43

see Figure S43 with photoluminescence decay curves). It is worth noting, that obtained values of lifetimes seems to be independent from substituent. Synthesized iridium complexes possess both an electron-donating groups (-OMe, -NH2), and an electron-withdrawing such as -CN or halogen – F, but the influence of these groups is rather insignificant. Obtained results are in good agreement with previously published for iridium complexes, whereas determined luminescence lifetimes was equal to 4.11 µs for [Ir(2,4-difluorophenylpyridine)2(4,4′-dimethylamino-2,2′bipyridine)](PF6).42 The radiative decay rates vary from 0.2 x 105 s-1 to 1.22 x 105 s-1 while the non-radiative decay rates lay between 0.96 x 105 s-1 and 2.06 x 105 s-1. Both constants are correlated with the nature of the substituents attached to ancillary as well as cyclometalating site and reveal the gradual drop of kr and the simultaneous rise of knr when moving from 1 to 8. It therefore brings to the conclusion that strongly electron accepting ligands at the ancillary site give the highest contribution to lower the QY, but when ppy ligand becomes fluorine-substituted it rises the QY significantly, what was expected.39

4. Electrochemistry Electrochemical properties of the studied species were investigated in CH2Cl2 solution by means of cyclic voltammetry (CV). The calculated HOMO, LUMO levels together with electrochemical energy band gap (Eg) are presented in Table 3. Since all of them are cationic with PF6- as a counterion in each case Bu4NPF6 was used as electrolyte to avoid undesired interactions. First, the electrochemical properties during oxidation were investigated. In all cases this process was found to be quasi-reversible in nature i.e. peak-to-peak separation values lying between 60 - 90 mV. Based on the onset values (Supporting Information - Table S9 and Figure 4) it can be immediately discovered that complexes composed of ppy ligands undergo oxidation


Page 15 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


much easier (of approximately 300 mV) than their corresponding 24dfppy counterparts. Since the difference is in each case almost the same it must be attributed to the presence of strongly electron-accepting fluorine atoms in the cyclometalating part. As expected, it causes the stabilization of both occupied phenyl molecular orbitals and iridium dπ orbitals39, hence it lifts the Eox value.

Table

3.

Comparison

of

the

electrochemical

and

theoretical

data

set

with

HOMO/LUMO/IP/EA/Eg levels obtained via cyclic voltammetry and DFT (in dichloromethane solution) at B3LYP/LANL2DZ/6-31G(d,p) level of theory. Cyclic voltammetry

DFT

Code

HOMOa,d (eV)

LUMOb,d (eV)

Egc (eV)

HOMO (eV)

LUMO (eV)

Eg (eV)

IP (eV)

EA (eV)

1

-5.75

-3.03

2.72

-5.64

-2.12

3.52

5.53

2.36

2

-6.04

-3.10

2.94

-5.98

-2.20

3.78

5.89

2.44

3

-5.93

-4.32

1.61

-5.74

-2.50

3.24

5.64

2.67

4

-6.16

-3.38

2.78

-6.08

-2.58

3.50

6.00

2.75

5

-5.86

-3.63

2.23

-5.84

-2.82

3.03

5.75

2.96

6

-6.23

-3.63

2.60

-6.19

-2.91

3.28

6.12

3.05

7

-5.94

-4.00

1.94

-5.98

-3.46

2.52

5.87

3.53

8

-6.23

-4.02

2.21

-6.32

-3.55

2.77

6.24

3.63

a

HOMO = -5.1 - Eox, b LUMO = -5.1 - Ered, c Eg = Eox(onset) − Ered(onset), d error based on the cyclic voltammetry measurements +/- 10 mV

On the other hand the effect of fluorine exchange on the ancillary ligand does not cause a substantial impact on the oxidation potential of the complex (especially in the case of 24dfppy



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 43

derivative). It clearly demonstrates that even without DFT results the radical cation must be formed on C^N ligand, where the N^N has only minor inductive impact on the HOMO level. On the contrary, the reduction follows a totally different pattern. First, there is no effect of the X substituent on the Ered value, with only the only exception of 3 and 4, where the difference is as high as 1V since 3 reduces anomalously easy i.e. Ered equal -0.78V! It is worth noting, that from a thermodynamic point of view the reduction of compounds 3-8 is fully reversible (approx. 60 mV peak-to-peak separation), but for 1 and 2 it is irreversible (Figure 4). For all but [Ir(ppy)2(44dmbpy)]PF6 (3), the reduction wave is strongly correlated with the ancillary bipyridine nature, with a very small affect from the cyclometalating ligand, what is evident on cyclic voltammograms in Figure 4. What is more, when more electron-accepting ligands are involved the reduction becomes multi-step covering three reversible processes for 7 and 8. There is therefore no doubt, that the HOMO is associated with C^N phenylpyridine moiety with some contribution from iridium metal center, while the LUMO lies exclusively on the ancillary ligand, which is further confirmed by DFT (Figure 5). This picture also reveals how the substituents affect the orbitals energies, which eventually determine the experimental behavior (cyclic voltammetry). Therefore one can easily establish, that moving from electron-donating to electron-accepting substituent on the ancillary site causes a gradual drop of the LUMO energy (from -2.20 eV for 2 to -3.55 eV for 8).


Page 17 of 43

20 1 3 5 7

15

Current (µ A)

10 5 0 -5 -10 -15 -20 -2,5

-2,0

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

0,5

1,0

1,5

+ E vs Fc/Fc (V)

20 2 4 6 8

15 10 Current (µ A)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5 0 -5 -10 -15 -20 -2,5

-2,0

-1,5

-1,0

-0,5

0,0

+ E vs Fc/Fc (V)

Figure 4. Cyclic voltammogramms of redox processes of complexes 1-8 (conditions: GC as working electrode, sweep rate ν = 100 mV/s, 0.2 M Bu4NPF6 in CH2Cl2) In pairs on the other hand their levels remain almost the same. Attaching fluorines on the cyclometalating site causes the HOMO level also to drop due to better stabilization of the electrons, which become more attracted to phenyl fragment. The energy is also independent on



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 43

the ancillary ligand type and is manifested as an 'up' and 'down' pattern in Figure 5. Beside simple HOMO/LUMO analysis it is worth to take a closer look on the ionization potential (IP) and electron affinity (EA) (see Supporting Information Figure S44). In this particular case the absolute values of HOMO energies (DFT) do not differ from the calculated IPs. For electron affinities there are only small differences from LUMOs (DFT) for 1 and 2 (0.24 eV) and 3 and 4 (0.17 eV). For species 5-8 the EAs are equal or almost equal to absolute LUMO levels. Spin density distributions (Figure S44) also support the aforementioned space separation of HOMO and LUMO. Finally, when it comes to compare the theoretical energies computed via DFT with the experimental data it is worth presenting it visually as theory vs. experiment plot (Figures S45 - S49). It can be easily seen that the HOMO (DFT) levels correspond qualitatively to the voltammetric measurements with small deviations of ca. 0.1 eV for species 1 and 0.2 eV for 3. In the case of LUMO levels the deviations are more pronounced, however with the exception of 3 the correlation is preserved. At this point it must be stated that DFT does not explain the strange behavior of [Ir(ppy)2(44dmbpy)]PF6 even in comparison with similar complexes containing 4,4'dimethoxy-2,2'-bipyridine, where E1/2red=-1.90 V.25


Page 19 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. Molecular orbital diagram of complexes 1-8 along with HOMO/LUMO plots computed at B3LYP/LANL2DZ/6-31G(d,p) level of theory (isosurface value = 0.03, green for positive and red negative sign). 5. Theoretical calculations Since the key issue of this paper was to study the photoluminescence of complexes 1-8 and its background several theoretical models of emission wavelength simulation were applied. In the first place it was investigated with the aid of Franck-Condon rule and state-specific solvation of the excited state in order to take into account all possible influencing factors. In parallel, simple ground-state triplet calculations were carried out for comparison. The data gathered in the abovementioned approaches was collected in Table 4.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 43

Table 4. Theoretical triplet-singlet emission energies computed via DFT ground-state and TDDFT approaches with linear response and state-specific solvation at B3LYP/LANL2DZ/631G(d,p) level of theory. No.

First triplet excited to ground state emission computed via linearresponse approach B3LYP (nm)

First triplet excited to ground state emission with state-specific solvation correction B3LYP (nm)

Emission energy computed via groundstate DFT approach B3LYP (nm)

1

567.75

573.66

528.72

2

543.20

547.46

503.03

3

626.57

983.49

585.96

4

542.85

546.39

502.53

5

697.04

1170.12

644.49

6

606.50

915.46

564.53

7

866.39

1697.23

803.12

8

730.51

1228.51

682.35

As one can easily notice each set of the calculations has its advantages, but also suffers from several drawbacks. At first it seems that the B3LYP approach is justified since it usually provides with fair match with the experiment. Herein, it brings a good quantitative agreement with linear response approach, however there are some exceptions from the expected pattern. First, the theoretical λemmax for 2 and 4 is almost identical: 543.20 nm and 542.85 nm, respectively. Besides that the rest of the complexes follow the trend set by the experimental findings with only deviation in the case of 5 and 8, where 5 is more blue-shifted in comparison to 8. When the state-specific approach is applied it does not bring significant improvement to the previous image as long as we consider complexes with high HOMO-LUMO gap or high


Page 21 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


emission energy.Otherwise, the calculated energy is lowered, which is expressed in higher wavelength values. As for comparison with experimental λemmax it is clear at first that there are some differences, which are especially pronounced for the aforementioned low-HOMO-LUMO gap compounds and for complex 2, which is classified as green-yellow emitter (543.20 nm). Since the problem seems to be connected with small HOMO-LUMO gap it can be assumed that it is associated with the amount of the Hartree-Fock exchange in the functional formula. The lower the HF XC part the less the electrons are localized and the lower the gap. For blue- and green-emitting compounds the effect is negligible (the differences of a few nm), but in the extreme situation of complexes 5-8 this part becomes crucial and the description of the excited state is poorer. On the other hand, the differences between the theory and the experiment (linear response) are easier to comprehend in electronvolts, since on average the theoretical values are c.a. 0.2 eV higher with the exception of 2 (0.42 eV), 7 (0.61 eV) and 8 (0.37 eV). Based on these unexpected results and recent findings on theoretical calculations of excited states98 a parallel study involving M06-2X functional was conducted. This change of functional was believed to bring reasonable results for complexes 5-8 due to the higher contribution of the HF exchange (50%). In fact however, the resulting correlation between the theory and the experiment was miscalculated and virtually no improvement to the B3LYP approach was brought. When the calculated emission wavelengths were plotted vs. the experimental ones it eventually turned out that the best match is reached for TD-B3LYP/LANL2DZ/6-31G(d,p) theory level with statespecific solvation as depicted in Figure 6 (the remaining data plots are available in Supporting Information Figures S50 - S53).



experimental

(nm)

600

λ

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 43

550

500

experimental

DFT

Y = 0.12X 2 R = 0.74598

+ 440

450 400

600

800

1000 DFT

λ

1200

1400

1600

1800

(nm)

Figure 6. Theoretical emission wavelengths calculated via TD-B3LYP/LANL2DZ/6-31G(d,p) level of theory with state-specific solvation vs. experimental values. As a final remark on the impact of the substituent effects on the localization of the triplet excited state, it is interesting to follow the contribution of the ligands and the metal center to the spin density of this state. According to spin density maps, its localization is highly connected with the nature of both the phenylpyridine moiety and the ancillary bipyridine. It appears that for 1, 2 and 4 the T1 is a 3MLCT state with a huge contribution from one of the cyclometalating ligands. On the contrary for the rest of the compounds it has more of the 3LC character, being spread over the bipyridine moiety. Base on the molecular orbital picture presented in Figure 5 the general structure of the complex may be taken either as a push-pull or pull-pull system. The cyclometalating site serves always as the pulling force, which is even stronger, when the fluoro substituents are attached. The Q moiety in the bipyridine structure can either attract (F, CN) or repel the electron density. The overall effect is a superposition of these two contributions. Therefore, for strongly push-pull systems (1, 2 and 4) the spin density occupies the cyclometalating site with some contribution from Ir mainly due to the strongly electron-donating


Page 23 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


character of 4,4'-diamino-2,2'-bipyridine and 4,4'-dimethoxy-2,2'-bipyridine. This effect is nevertheless more pronounced for 44dabpy, which is donating enough to push the spin density even without the enhanced attraction from the phenylpyridine in the case of 1. Up from [Ir(ppy)2(44dmbpy)]PF6 the situation becomes inverted and the triplet excited state is more delocalized favoring the accepting bipyridine site. The exemplary comparison between 3 and 4 is presented in Figure 7 (full picture in Figure S54 Supporting Information). These findings are consistent with similar calculations of cationic iridium cyclometalates74, however made only for complexes with electron-accepting ancillary ligand.

Figure 7. Spin densities of triplet excited states for complexes 3 and 4 obtained at B3LYP/LANL2DZ/6-31G(d,p) level of theory (isosurface value = 0.001, green for positive and blue for negative sign). CONCLUSIONS To summarize, we have synthesized a series of eight iridium(III) cyclometalates consisting of two different cyclometalting ligands: 2-phenylpyridine or 2-(2,4-diflurophenyl)pyridine and various electron-accepting and electron-donating 4,4'-subistituted 2,2'-bipyridines. On the ready material we have tested the impact of the ligand structure tuning on emission wavelength maximum position, quantum yield magnitude and HOMO-LUMO gap adjusting through substituent-related effects. It was found that the careful choice of the ligands fine-tune both emission color and quantum yield at once. For electron-donating 2,2'-bipyridines the λem was



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 43

significantly blue-shifted covering blue and blue-green region, while the rest of the spectrum was filled when complexes with electron-withdrawing ligands were applied. Surprisingly, no effect was observed on the excited states lifetimes. The emission study was also consistent with electrochemical measurements (with only one exception), which revealed basic assumptions on the HOMO/LUMO localization and stabilization/destabilization. Moreover, what is crucial for practical applications in most of the cases both redox processes were fully reversible. All these findings were also supported by comprehensive DFT and TD-DFT study with static and dynamic solvation. Theoretical calculations enabled to build a qualitative model, which allows to efficiently predict the HOMO/LUMO positions and emission wavelength maximum prior to the synthesis, which can significantly reduce its costs. This model may find applications in OLED and LEC technology based on iridium cyclometalates. In order to gain more complexity it will be further developed in the upcoming papers involving broader data set and more advanced theoretical techniques.

ASSOCIATED CONTENT Supporting Information. All experimental and safety procedures, 1H NMR,

13

C NMR and

Mass Spectra together with detailed DFT calculations are provided with comprehensive attachment. Cartesian coordinates calculated via Link202 are given in a separate text file. CCDC 934474 (3), CCDC 934476 (7), CCDC 934477 (6) and CCDC 934478 (8*) contain the supplementary crystallographic data for the complexes given in brackets. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44


Page 25 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1223-336-033; or e-mail:[email protected]. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *

E-mail: [email protected] Tel.: +48222345584

Notes The authors declare no competing financial interests. ACKNOWLEDGMENTS This research was carried out in the framework of the National Centre for Research and Development financial support (No. PBS2/A5/40/2014). The Gaussian09 calculations were carried out in the Wroclaw Centre for Networking and Supercomputing, WCSS, Wroclaw, Poland. http://www.wcss.wroc.pl, under calculational Grant No. 283. REFERENCES (1) Bujak, P.; Kulszewicz-Bajer, I.; Zagorska, M.; Maurel, V.; Wielgus, I.; Pron, A. Polymers for Electronics and Spintronics. Chem. Soc. Rev. 2013, 42, 8895-8999. (2) Pron, A.; Gawrys, P.; Zagorska, M.; Djurado, D.; Demadrille, R. Electroactive Materials for Organic Electronics: Preparation Strategies, Structural Aspects and Characterization Techniques. Chem. Soc. Rev. 2010, 39, 2577-2632.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 43

(3) Choy, W. C. H.; Chan, W. K.; Yuan, Y. Recent Advances in Transition Metal Complexes and Light-Management Engineering in Organic Optoelectronic Devices. Adv. Mater. 2014, 26, 5368-5399. (4) Dobbs, K. D.; Feldman, J.; Marshall, W. J.; McLain, S. J.; McLaren, C. D.; Meth, J. S.; Vo, G. D.; Wang, Y. Phosphorescent Iridium(III) Complexes of Cyclometalated 5-Aryl-1H-1,2,4Triazole Ligands: Structural, Computational, Spectroscopic, and Device Studies. J. Phys. Chem. C 2014, 118, 27763−27771. (5) Lee, S.; Kim, S. -O.; Shin, H.; Yun, H. -J.; Yang, K.; Kwon, S. -K.; Kim, J. -J.; Kim, Y. H. Deep-Blue Phosphorescence from Perfluoro Carbonyl-Substituted Iridium Complexes. J. Am. Chem. Soc. 2013, 135, 14321-14328. (6) Zhang, K.; Chen, Z.; Yang, C.; Zou, Y.; Gong, S.; Qin, J.; Cao, Y. First Iridium Complex End-Capped Polyfluorene: Improving Device Performance for Phosphorescent Polymer LightEmitting Diodes. J. Phys. Chem. C 2008, 112, 3907-3913. (7) Adachi, C.; Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Nearly 100% Internal Phosphorescence Efficiency in an Organic Light Emitting Device. J. Appl. Phys. 2001, 90, 50485051. (8) Fan, C.; Zhu, L.; Jiang, B.; Li, Y.; Zhao, F. Ma, D.; Qin, J.; Yang, C. High Power Efficiency Yellow Phosphorescent OLEDs by Using New Iridium Complexes with HalogenSubstituted 2-Phenylbenzo[d]thiazole Ligands. J. Phys. Chem. C 2013, 117, 19134−19141. (9) Yang, C. H.; Cheng, Y. M.; Chi, Y.; Hsu, C. J.; Fang, F. C.; Wong, K. T.; Chou, P. T.; Chang, C. H.; Tsai, M. H.; Wu, C. C. Blue-Emitting Heteroleptic Iridium(III) Complexes


Page 27 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Suitable for High-Efficiency Phosphorescent OLEDs. Angew. Chem.Int. Ed. 2007, 46, 24182421. (10) Liu, S.-J.; Zhao, Q.; Deng, Y.; Xia, Y.-J.; Lin, J.; Fan. Q.-L. Wang, L.-H.; Huang, W. πConjugated Chelating Polymers with a Charged Iridium Complex in the Backbones: Toward Saturated-Red Phosphorescent Polymer Light-Emitting Diodes. J. Phys. Chem. C 2007, 111, 1166-1175. (11) Song, M.; Park, J. S.; Gal, Y.-S.; Kang, S.; Lee, J. Y.; Lee, J. W.; Jin, S.-H. Homologous Series of Phenylquinoline-Carbazole Main Ligand Based On Red-Emitting Iridium(III) Complexes for Phosphorescent Organic Light-Emitting Diodes. J. Phys. Chem. C 2012, 116, 7526−7533. (12) Gutierrez-Llorente, A.; Arredondo, B.; Romero, B. Energy Transfer within Mixed Phase Polyfluorene Based Phosphorescent Electroluminescent Devices. J. Phys. Chem. C 2012, 116, 4259−4266. (13) Park, Y.-S.; Kang, J.-W.; Kang, D. M.; Park, J.-W.; Kim, Y.-H.; Kwon, S.-K.; Kim, J.-J. Efficient, Color Stable White Organic Light-Emitting Diode Based on High Energy Level Yellowish-Green Dopants. Adv. Mater. 2008, 20, 1957-1961. (14) Leem, D.-S.; Jung, S. O.; Kim, S.-O.; Park, J.-W.; Kim, J. W.; Park, Y.-S.; Kim, Y.-H.; Kwon, S. K.; Kim, J.-J. Highly Efficient Orange Organic Light-emitting Diodes Using a Novel Iridium Complex with Imide Group-Containing Ligands. J. Mater. Chem. 2009, 19, 8824-8828. (15) Kang, D. M.; Park, J. W.; Jung, S. O.; Lee, S. H.; Park, H. D.; Kim, Y. H.; Shin, S. C.; Kim, J.-J.; Kwon, S. K. Iridium Complexes with Cyclometalated 2-Cycloalkenyl-Pyridine



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 43

Ligands as Highly Efficient Emitters for Organic Light-Emitting Diodes. Adv. Mater. 2008, 20, 2003-2007. (16) Tanaka, D.; Sasabe, H.; Li, Y.-J.; Su, S.-J.; Takeda, T.; Kido, J. Ultra High Efficiency Green Organic Light-Emitting Devices. Jpn. J. Appl. Phys. 2007, 46, L10-L12. (17) Tao, R.; Qiao, J.; Zhang, G.; Duan, L.; Wang. L.; Qiu, Y. Efficient Near-Infrared-Emitting Cationic Iridium Complexes as Dopants for OLEDs with Small Efficiency Roll-off. J. Phys. Chem. C 2012, 116, 11658−11664. (18) Rai, V. K.; Nishiura, M.; Takimoto, M.; Zhao, S.; Liu, Y.; Hou, Z. Bis-Cyclometalated Iridium(III) Complexes Bearing Ancillary Guanidinate Ligands. Synthesis, Structure, and Highly Efficient Electroluminescence. Inorg. Chem. 2012, 51, 822−835. (19) Kozhevnikov, V. N.; Zheng, Y.; Clough, M.; Al-Attar, H.; Griffiths, G. C.; Abdullah, K.; Raisys, S.; Jankus, V.; Bryce, M. R.; Monkman, A. P. Cyclometalated Ir(III) Complexes for High-Efficiency Solution-Processable Blue PhOLEDs. Chem. Mater. 2013, 25, 2352-2358. (20) Wang, Y.-M.; Teng. F.; Gan, L.-H.; Liu, H.-M.; Zhang, X.-H.; Fu, W.-F.; Wang, Y.-S.; Xu, X.-R. Blue Light-Emitting Bisorthometalated Ir(III) Complex: Origin of Blue Emission and Application in Electrophosphorescent Devices. J. Phys. Chem. C 2008, 112, 4743-4747. (21) Minaev, B.; Baryshnikov, G.; Agren, H. Principles of Phosphorescent Organic Light Emitting Devices. Phys. Chem. Chem. Phys. 2014, 16, 1719-1758. (22) Bejoymohandas, K. S.; Kumar, A.; Varughese, S.; Varathan, E.; Subramanian, V.; Reddy, M. L. P. Photophysical and Electroluminescence Properties of bis(2',6'-Difluoro-2,3'bipyridinato-N,C4')iridium-(picolinate) Complexes: Effect of Electron-Withdrawing and


Page 29 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Electron-Donating Group Substituents at the 4' Position of the Pyridyl Moiety of the Cyclometalated Ligand. J. Mater. Chem. C, 2015, 3, 7405-7420. (23) Fernandez-Hernandez, J. M.; Beltran, J. I.; Lemaur, V.; Galvez-Lopez, M. -D.; Chien, C. H.; Polo, F.; Orselli, E.; Frohlich, R.; Cornil, J.; De Cola, L. Iridium(III) Emitters Based on 1,4Disubstituted-1H-1,2,3-triazoles as Cyclometalating Ligand: Synthesis, Characterization, and Electroluminescent Devices. Inorg. Chem. 2013, 52, 1812-1824. (24) Lowry, M. S.; Goldsmith, J. I.; Slinker, J. D.; Rohl, R.; Pascal, R. A., Jr.; Malliaras, G. G.; Bernhard, S. Single-Layer Electroluminescent Devices and Photoinduced Hydrogen Production from an Ionic Iridium(III) Complex. Chem. Mater. 2005, 17, 5712-5719. (25) Tamayo, A. B.; Garon, S.; Sajoto, T.; Djurovich P. I.; Tsyba, I. M.; Bau, R.; Thompson, M. E. Cationic bis-Cyclometalated Iridium(III) Diimine Complexes and Their Use in Efficient Blue, Green, and Red Electroluminescent Devices. Inorg. Chem. 2005, 44, 8723-8732. (26) Nazeeruddin, Md. K.; Wegh, R. T.; Zhou, Z.; Klein, C.; Wang, Q.; De Angelis, F.; Fantacci, S.; Gratzel, M. Efficient Green-Blue-Light-Emitting Cationic Iridium Complex for Light-Emitting Electrochemical Cells. Inorg. Chem. 2006, 45, 9245-9250. (27) Rotche, C.; Chiang, C. -J.; Jankus, V.; Abdullah, K.; Zeng, X.; Jitchati, R.; Batsanov, A. S.; Bryce, M. R.; Monkman, A. P. Ionic Iridium(III) Complexes with Bulky Side Groups for Use in Light Emitting Cells: Reduction of Concentration Quenching. Adv. Funct. Mater. 2009, 19, 2038-2044.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 43

(28) Costa, R. D.; Orti, E.; Bolink, H. J.; Graber, S.; Schaffner, S.; Neuburger, M.; Housecroft, C. E.; Constable, E. C. Archetype Cationic Iridium Complexes and Their Use in Solid-State Light-Emitting Electrochemical Cells. Adv. Funct. Mater. 2009, 19, 3456-3463. (29) Margapoti, E.; Shukla, V.; Valore, A.; Sharma, A.; Dragonetti, C.; Kittis, C. C.; Roberto, D.; Murgia, M.; Ugo, R.; Muccini. M.; Excimer Emission in Single Layer Electroluminescent Devices Based on [Ir(4,5-diphenyl-2-methylthiazolo)2(5-methyl-1,10-phenanthroline)]+ [PF6]-. J. Phys. Chem. C 2009, 113, 12517–12522. (30) Dedeian, K.; Djurovich, P. I.; Garces, F. O.; Carlson, G.; Watts, R. J. A New Synthetic Route to the Preparation of a Series of Strong Photoreducing Agents: fac Tris-Ortho-Metalated Complexes of Iridium(III) with Substituted 2-Phenylpyridines. Inorg. Chem. 1991, 30, 16851687. (31) Mondal, S.; Seth, K. S.; Gupta, P.; Purkayastha, P. Ultrafast Photoinduced Electron Transfer between Carbon Nanoparticles and Cyclometalated Rhodium and Iridium Complexes. J. Phys. Chem. C 2015, 119, 25122−25128. (32) Klein, J. H.; Sunderland, T. L.; Kaufmann, C.; Holzapefel, M.; Schmiedel. A.; Lambert, C. Stepwise versus Pseudo-Concerted Two-Electron-Transfer in a Triarylamine–Iridium Dipyrrin–Naphthalene Diimide Triad. Phys. Chem. Chem. Phys. 2013, 15, 16024-16030. (33) Klein. J. H.; Schmidt, D.; Steiner, U. E.; Lambert, C. Complete Monitoring of Coherent and Incoherent Spin Flip Domains in the Recombination of Charge-Separated States of DonorIridium Complex-Acceptor Triads. J. Am. Chem. Soc. 2015, 137, 11011−11021.


Page 31 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(34) Miomandre, F.; Stancheva, S.; Audibert, J.-F.; Brosseau, A.; Pansu, R. B.; Lepeltier, M.; Mayer, C. R. Gold and Silver Nanoparticles Functionalized by Luminescent Iridium Complexes: Synthesis and Photophysical and Electrofluorochromic Properties J. Phys. Chem. C 2013, 117, 12806-12814. (35) Liu, R.; Dandu, N.; Chen, J.; Li, Y.; Li, Z.; Liu, S.; Wang, C.; Kilina, S.; Kohler, B.; Sun, W. Influence of Different Diimine (N∧N) Ligands on the Photophysics and Reverse Saturable Absorption of Heteroleptic Cationic Iridium(III) Complexes Bearing Cyclometalating 2‑{3-[7(Benzothiazol-2-yl)fluoren-2-yl]phenyl}pyridine (C∧N) Ligands. J. Phys. Chem. C 2014, 118, 23233-23246. (36) Li, Y.; Dandu, N.; Liu, R.; Li, Z.; Kilina, S.; Sun, W. Effects of Extended π‑Conjugation in Phenanthroline (N∧N) and Phenylpyridine (C∧N) Ligands on the Photophysics and Reverse Saturable Absorption of Cationic Heteroleptic Iridium(III) Complexes. J. Phys. Chem. C 2014, 118, 6372−6384. (37) Lowry, M. S.; Bernhard, S. Synthetically Tailored Excited States: Phosphorescent, Cyclometalated Iridium(III) Complexes and Their Applications. Chem. Eur. J. 2006, 12, 79707977. (38) Costa, R. D.; Orti, E.; Bolink, H. J.; Monti, F.; Accorsi, G.; Armaroli, N. Luminescent Ionic Transition-Metal Complexes for Light-Emitting Electrochemical Cells. Angew. Chem. Int. Ed. 2012, 51, 8178-8211. (39) Chi, Y.; Chou, P.-T. Transition-Metal Phosphors with Cyclometalating Ligands: Fundamentals and Applications. Chem. Soc. Rev. 2009, 39, 638-655.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 43

(40) You, Y.; Park, S. Y. Phosphorescent Iridium(III) Complexes: toward High Phosphorescence Quantum Efficiency through Ligand Control. Dalton Trans. 2009, 1267-1282. (41) Ulbricht, Ch.; Beyer, B.; Friebe, Ch.; Winter, A.; Schubert, U. S. Recent Developments in the Application of Phosphorescent Iridium(III) Complex Systems. Adv. Mater. 2009, 21, 44184441. (42) De Angelis, F.; Fantacci, S.; Evans, N.; Klein, C.; Zakeeruddin, S. M.; Moser, J.-E.; Kalyanasundaram, K.; Bolink, H. J.; Gratzel, M.; Nazeeruddin, Md. K. Controlling Phosphorescence Color and Quantum Yields in Cationic Iridium Complexes: A Combined Experimental and Theoretical Study. Inorg. Chem. 2007, 46, 5989-6001. (43) Yang, C.-H.; Beltran, J.; Lemaur, V.; Cornil, J.; Hartmann, D.; Sarfert, W.; Frohlich, R.; Bizzarri, C.; De Cola, L. Iridium Metal Complexes Containing N-Heterocyclic Carbene Ligands for Blue-Light-Emitting Electrochemical Cells. Inorg. Chem., 2010, 49, 9891-9901. (44) de Queiroz, T. B.; Botelho, M. B. S.; Fernandez-Hernandez, J. M.; Eckert, H.; Albouquerque, R. Q.; de Camargo, A. S. S.; New Luminescent Host-Guest System Based on an Iridium(III) Complex: Design, Synthesis, and Theoretical-Experimental Spectroscopic Characterization. J. Phys. Chem. C 2013, 117, 2966−2975. (45) Vella, J. H.; Parthasarathy, A.; Schanze, K. S.; Triplet Sensitization in an Anionic Poly(phenyleneethynylene) Conjugated Polyelectrolyte by Cationic Iridium Complexes. J. Phys. Chem. A 2013, 117, 7818−7822. (46) Srivastava, R.; Joshi, L. R. The Effect of Substituted 1,2,4-Triazole Moiety on the Emission, Phosphorescent Properties of the Blue Emitting Heteroleptic Iridium(III) Complexes


Page 33 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and the OLED Performance: a Theoretical Study. Phys. Chem. Chem. Phys. 2014, 16, 1728417294. (47) Costa, R. D.; Casillas, R.; Cano, J. Do the Intramolecular π Interactions Improve the Stability of Ionic, Pyridine-Carbene-Based Iridium(III) Complexes? J. Phys. Chem. C 2013, 117, 8545−8555. (48) Hwang, A.-R.; Han, W.-S.; Wee, K.-R.; Kim, H. Y.; Cho, D. W.; Min, B. K.; Nam, S. W.; Pac, C.; Kang, S. O. Photodynamic Behavior of Heteroleptic Ir(III) Complexes with CarbazoleFunctionalized Dendrons Associated with Efficient Electron Transfer Processes. J. Phys. Chem. C 2012, 116, 1973–1986. (49) Bolink, H. J.; De Angelis, F.; Baranoff, E.; Klein, C.; Fantacci, S.; Coronado, E.; Sessolo, M.; Kalyanasundaram, K.; Gratzel, M.; Nazeeruddin, Md. K. White-Light Phosphorescence Emission from a Single Molecule: Application to OLED. Chem. Commun. 2009, 4672−4674. (50) Tsai, H.-R.; Lu, K.-Y.; Lai, S.-H.; Fan, C.-H.; Cheng, C.-H.; Chen, I.-C. Metal-Ligand Bonding Strength of Fluoro-Substituted Cyclometalated Iridium(III) Complexes from Raman and Infrared Spectra. J. Phys. Chem. C 2011, 115, 17163–17174. (51) Shin, I.-S.; Kim. J. I.; Kwon, T.-H.; Hong, J.-I.; Lee, J.-K.; Kim, H. Efficient Electrogenerated Chemiluminescence from bis-Cyclometalated Iridium(III) Complexes with Substituted 2-Phenylquinoline Ligands. J. Phys. Chem. C 2007, 111, 2280-2286. (52) You,Y.; Kim. K. S.; Ahn, T. K.; Kim, D.; Park, S. Y. Direct Spectroscopic Observation of Interligand Energy Transfer in Cyclometalated Heteroleptic Iridium(III) Complexes: A Strategy



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 43

for Phosphorescence Color Tuning and White Light Generation. J. Phys. Chem. C 2007, 111, 4052-4060. (53) Godefroid, G.; Juanjuan, S.; Yuqi, L.; Xiochun, Q.; Yanling, S.; Xiaohong, S.; Shijian, W. Combined Effects of Stereoisomeric and Steric Factors on Electronic and Photophysical Properties of Bis-cyclometalated Ir(III) Complexes Containing 2,5-Diaryl-1,3,4-oxadiazole Based and Picolinate Ligands. J. Phys. Chem. C 2012, 116, 14575−14583. (54) Gu, X.; Fei, T.; Zhang, H.; Xu, H.; Yang, B.; Ma, Y.; Liu, X.; Theoretical Studies of BlueEmitting Iridium Complexes with Different Ancillary Ligands. J. Phys. Chem. A 2008, 112, 8387–8393. (55) Cortes-Arriagada, D.; Sanhueza, L.; Gonzalez, I.; Dreyse, P.; Toro-Labbe, A. About the Electronic and Photophysical Properties of Iridium(III)-Pyrazino[2,3-f ][1,10]-phenanthroline Based Complexes for Use in Electroluminescent Devices. Phys. Chem. Chem. Phys. 2016, 18, 726-734. (56) Shvaleev, N. M.; Monti, F.; Scopelliti, R.; Amaroli, N.; Gratzel, M.; Nazeeruddin, Md. K. Blue Phosphorescence of Trifluoromethyl- and Trifluoromethoxy-Substituted Cationic Iridium(III) Isocyanide Complexes. Organometallics 2012, 31, 6288-6296. (57) Shavaleev, N. M.; Monti, F.; Costa, R. D.; Scopelliti, R.; Bolink, H. J.; Orti, E.; Accorsi, G.; Armaroli, N.; Baranoff, E.; Gratzel, M.; Nazeeruddin, Md. K. Bright Blue Phosphorescence from Cationic Bis-Cyclometalated Iridium(III) Isocyanide Complexes. Inorg. Chem. 2012, 51, 2263−2271.


Page 35 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(58) Baranoff, E.; Yum, J. -H.; Gratzel, M.; Nazeeruddin, Md. K. Cyclometallated Iridium Complexes for Conversion of Light into Electricity and Electricity into Light. J. Organomet. Chem. 2009, 694, 2661-2670. (59) De Angelis, F.; Belpassi, L.; Fantacci, S. Spectroscopic Properties of Cyclometallated Iridium Complexes by TDDFT. J. Mol. Struc.-THEOCHEM 2009, 914, 74-86. (60) Li, X.-N.; Wu, Z.-J.; Si, Z.-J.; Zhang, H.-J.; Zhou, L.; Liu, X.-J. Injection, Transport, Absorption and Phosphorescence Properties of a Series of Blue-Emitting Ir(III) Emitters in OLEDs: a DFT and Time-Dependent DFT Study. Inorg. Chem. 2009, 48, 7740-7749. (61) Hay, P. J. Theoretical Studies of the Ground and Excited Electronic States in Cyclometalated Phenylpyridine Ir(III) Complexes Using Density Functional Theory. J. Phys. Chem. A 2002, 106, 1634-1641. (62) Zhang, S.; Si, Y.; Wu, Z. Theoretical Study on the Effect of Different Substituents on the Electronic Structures and Photophysical Properties of Phosphorescent Ir(III) Complexes. RSC Adv. 2014, 4, 15849-15855. (63) Liu, Y.; Sun, X.; Si, Y.; Qu, X.; Wang, Y.; Wu, Z. Tuning the Electronic Properties and Quantum Efficiency of Blue Ir(III) Carbene Complexes via Different Azole-Pyridine-Based N^N' Ligands. RSC Adv. 2014, 4, 6284-6292. (64) Shang, X. -H.; Liu, Y. -Q.; Su, J. -J. Gahungu, G.; Qu, X. -C.; Wu, Z. -J. Theoretical Study on the Electronic Structures and Optical Properties of Blue-Green and Blue Phosphorescent Iridium(III) Complexes with Tetraphenylimidodiphosphinate Ligand. Int. J. Quantum. Chem. 2014, 114, 183–191.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 43

(65) Si, Y.; Sun, X.; Liu, Y.; Qu, X.; Wang, Y.; Wu, Z. A DFT/TDDFT Study on the Effect of CN Substitution on Color Tuning and Phosphorescence Efficiency of a Series of Ir(III) Complexes with Phosphine-Silanolate Ligands. Dalton Trans. 2014, 43, 714–721. (66) Kwon, T. -H.; Cho, H. S.; Kim, K. M.; Kim, J. -W.; Kim, J. -J.; Lee, K. H.; Park, S. J.; Shin, I. -S.; Kim, H.; Shin, D. M.; Chung, Y. K.; Hong, J. -I. Color Tuning of Cyclometalated Iridium Complexes through Modification of Phenylpyrazole Derivatives and Ancillary Ligand Based on ab Initio Calculations. Organometallics 2005, 24, 1578-1585. (67) Yersin, H.; Hofbeck, T. The Triplet State of fac-Ir(ppy)3. Inorg. Chem. 2010, 49, 9290– 9299. (68) Terki, R.; Simoneau, L.-P.; Rocheroft, A. Tailoring the Photoluminescence Properties of Ionic Iridium Complexes. J. Phys. Chem. A 2009, 113, 534–541. (69) Kadari, A.; Moncomble, A.; Ciofini, I.; Brahimi, M.; Adamo, C. Theoretical Study of Absorption and Emission Properties of Green and Yellow Emitting Iridium(III) Complexes. J. Phys. Chem. A 2011, 115, 11861–11865. (70) Li, X.-N.; Wu, Z.-J. Liu, X.-J.; Zhang, H.-J. Origin of Rare and Highly Efficient Phosphorescent and Electroluminescent Iridium(III) Complexes Based on C∧N=N Ligands, A Theoretical Explanation. J. Phys. Chem. A 2010, 114, 9300–9308. (71) Shi, L.; Wei, Hong, B.; Guan, W.; Wu, Z.; Su, Z. DFT/TD-DFT Study on the Electronic Structures and Optoelectronic Properties of Several Blue-Emitting Iridium(III) Complexes. J. Phys. Chem. A 2010, 114, 6559–6564.


Page 37 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(72) Wang, J.; Bai, F.-Q.; Xia, B.-H.; Zhang, H.-X. Efficient Blue-Emitting Ir(III) Complexes with Phosphine Carbanion-Based Ancillary Ligand: A DFT Study. J. Phys. Chem. A 2011, 115, 11689–11695. (73) Cramer, C. J.; Truhlar, D. G. Density Functional Theory for Transition Metals and Transition Metal Chemistry. Phys. Chem. Chem. Phys. 2009, 11, 10757–10816. (74) Chirdon, D. N.; McCusker, C. E.; Castellano, F. N.; Bernhard, S. Tracking of Tuning Effects in Bis-Cyclometalated Iridium Complexes: A Combined Time Resolved Infrared Spectroscopy, Electrochemical, and Computational Study. Inorg. Chem. 2013, 52, 8795−8804. (75) Matsushita, T.; Asada, T.; Koseki, S. Relativistic Study on Emission Mechanism in Tris(2-phenylpyridine)iridium. J. Phys. Chem. C 2007, 111, 6897-6903. (76) Younker, J. M.; Dobbs, K. D. Correlating Experimental Photophysical Properties of Iridium(III) Complexes to Spin−Orbit Coupled TDDFT Predictions. J. Phys. Chem. C 2013, 117, 25714−25723.

(77) Koseki, S.; Kamata, N.; Asada, T.; Yagi, S.; Nakazumi, H.; Matsushita, T. Spin−Orbit Coupling Analyses of the Geometrical Effects on Phosphorescence in Ir(ppy)3 and Its Derivatives. J. Phys. Chem. C 2013, 117, 5314−5327. (78) Wang. L.; Wu, Y.; Geng, Y.; Wu, J.; Zhu, D.-X.; Su, Z.-M. Shedding Light on the Photophysical Properties of Iridium(III) Complexes with N-Heterocyclic Carbene Ligands from a Theoretical Viewpoint. J. Phys. Chem. A 2014, 118, 5058−5067.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 43

(79) Minaev, B.; Minaeva, V.; Agren, H. Theoretical Study of the Cyclometalated Iridium(III) Complexes Used as Chromophores for Organic Light-Emitting Diodes. J. Phys. Chem. A 2009, 113, 726–735. (80) Kozhevnikov, V. N.; Dahms, K.; Bryce, M. R. Nucleophilic Substitution of Fluorine Atoms

in

2,6-Difluoro-3-(pyridin-2-yl)benzonitrile

Leading

to

Soluble

Blue-Emitting

Cyclometalated Ir(III) Complexes. J. Org. Chem. 2011, 76, 5143–5148. (81) Edkins, R. M.; Fucke, K.; Peach, M. J. G.; Crawford, A. G.; Marder, T. B.; Beeby, A. Syntheses, Structures, and Comparison of the Photophysical Properties of Cyclometalated Iridium Complexes Containing the Isomeric 1- and 2-(2-Pyridyl)pyrene Ligands. Inorg. Chem. 2013, 52, 9842−9860. (82) Constable, E. C.; Neuburger, M.; Rosel, P.; Schneider, G. E.; Zampese, J. A.; Housecroft, C. E.; Monti, F.; Armaroli, N.; Costa, R. D.; Orti, E. Ligand-Based Charge-Transfer Luminescence in Ionic Cyclometalated Iridium(III) Complexes Bearing a Pyrene-Functionalized Bipyridine Ligand: A Joint Theoretical and Experimental Study. Inorg.Chem. 2013, 52, 885−897. (83) Schwartz, K. R.; Chitta, R.; Bohnsack, J. N.; Ceckanowicz, D. J.; Miro, P.; Cramer, C. J.; Mann, K. R. Effect of Axially Projected Oligothiophene Pendants and Nitro-Functionalized Diimine Ligands on the Lowest Excited State in Cationic Ir(III) bis-Cyclometalates. Inorg. Chem. 2012, 51, 5082–5094. (84) Hesterberg, T. W.; Yang, X.; Holliday. G. J. Polymerizable Cationic Iridium(III) Complexes Exhibiting Color Tunable Light Emission and Their Corresponding Conducting Metallopolymers. Polyhedron 2010, 29, 110–115.


Page 39 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(85) Mi, B. X.; Wang, P. F.; Gao, Z. Q.; Lee, C. S.; Lee, S. T.; Hong, H. L.; Chen, X. M.; Wong, M . S.; Xia, P. F.; Cheah, K. W.; Chen, C. H.; Huang, W. Strong Luminescent Iridium Complexes with C^N=N Structure in Ligands and Their Potential in Efficient and Thermally Stable Phosphorescent OLEDs. Adv. Mater. 2009, 21, 339–343. (86) Zhao, Q.; Liu, S.; Shi, M.; Wang. C.; Yu, M.; Li. L.; Li. F.; Yi, T.; Huang. C. Series of New Cationic Iridium(III) Complexes with Tunable Emission Wavelength and Excited State Properties: Structures, Theoretical Calculations, and Photophysical and Electrochemical Properties. Inorg. Chem. 2006, 45, 6152-6160. (87) Fernandez-Hernandez, J. M.; Yang, C. -H.; Beltran, J. I.; Lemaur, V.; Polo, F.; Frohlich, R.; Cornil, J.; De Cola, L. Control of the Mutual Arrangement of Cyclometalated Ligands in Cationic Iridium(III) Complexes. Synthesis, Spectroscopy, and Electroluminescence of the Different Isomers. J. Am. Chem. Soc. 2011, 133, 10543–10558. (88) Sivasubramaniam, V.; Brodkorb, F.; Hanning, S.; Loebl, H. P.; van Elsbergen, V.; Boerner, H.; Scherf, U.; Kreyenschmidt, M. Fluorine Cleavage of the Light Blue Heteroleptic Triplet Emitter FIrpic. J. Fluor. Chem. 2009, 130, 640-649. (89) Sivasubramaniam, V.; Brodkorb, F.; Hanning, S.; Loebl, H. P.; van Elsbergen, V.; Boerner, H.; Scherf, U.; Kreyenschmidt, M. Investigation of FIrpic in PhOLEDs via LC/MS Technique. Cent. Eur. J. Chem. 2009, 7, 836–845. (90) Tordera, D.; Serrano-Perez, J. J.; Pertegas, A.; Orti, E.; Bolink, H. J.; Baranoff, E.; Nazeeruddin, Md. K.; Frey, J. Correlating the Lifetime and Fluorine Content of Iridium(III) Emitters in Green Light-Emitting Electrochemical Cells. Chem. Mater. 2013, 25, 3391−3397.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 43

(91) Mills, I. N.; Kagalwala, H. N.; Chirdon, D. N.; Brooks, A. C.; Bernhard, S. New Ir(III) 4,4'-Dicyano-2,2'-bipyridine Photosensitizers for Solar Fuel Generation. Polyhedron 2014, 82, 104-108. (92) Ma, D.-L.; Liu, L.-J.; Leung, K.-H.; Chen, Y.-T.; Zhong, H.-J.; Chan, D. S.-H.; Wang, H.M. D.; Leung, C.-H. Antagonizing STAT3 Dimerization with a Rhodium(III) Complex. Angew. Chem. Int. Ed. 2014, 53, 9178-9182. (93) Wu, Z.; Mu, J.; Wang, Q.; Chen, X.; Jensen, L.; Yi, C.; Li, M.-J. Hydroxyl and Amino Functionalized Cyclometalated Ir(III) Complexes: Synthesis, Characterization and Cytotoxicity Studies. J. Organomet. Chem. 2015, 791, 175-182. (94) Ladouceur, S.; Fortin, D.; Zysman-Colman, E. Enhanced Luminescent Iridium(III) Complexes Bearing Aryltriazole Cyclometallated Ligands. Inorg. Chem. 2011, 50, 11514-11526. (95) Monti, F.; Baschieri, A.; Gualandi, I.; Serrano-Perez, J. J.; Junquera-Hernandez, J. M.; Tonelli, D.; Mazzanti, A.; Muzzioli, Stagni, S.; Roldan-Carmona C.; Pertegas, A.; Bolink H. J.; Orti. E.; Sambri, L.; Armaroli, N. Iridium(III) Complexes with Phenyl-Tetrazoles as Cyclometalating Ligands. Inorg. Chem. 2014, 53, 7709−7721. (96) Zanoni, K. P. S.; Kariyazaki, B. K.; Ito, A.; Brennaman, M. K.; Meyer, T. J.; Iha, N. Y. M. Blue-Green Iridium(III) Emitter and Comprehensive Photophysical Elucidation of Heteroleptic Cyclometalated Iridium(III) Complexes. Inorg. Chem. 2014, 53, 4089−4099. (97) He. L.; Duan, L.; Qiao, J.; Wang R.; Wei. P.; Wang, L.; Qiu, Y. Blue-Emitting Cationic Iridium Complexes with 2-(1H-Pyrazol-1-yl)pyridine as the Ancillary Ligand for Efficient LightEmitting Electrochemical Cells. Adv. Funct. Mater. 2008, 18, 2123–2131.


Page 41 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(98) van Meer, R.; Gritsenko, O. V.; Baerends, E. J. Physical Meaning of Virtual Kohn−Sham Orbitals and Orbital Energies: An Ideal Basis for the Description of Molecular Excitations. J. Chem. Theory Comput. 2014, 10, 4432-4441.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 43

For Table of Contents Only Table of Contents Synopsis A comprehensive study on the design, synthesis and comprehensive characterization of highly emissive cationic iridium(III) cyclometalates is presented. The high color fine-tuning and HOMO/LUMO adjusting are obtained through electron-accepting/donating character of the ligands and a careful choice of the attached substituents. Finally, based on the DFT calculations a phenomenological model between theory and experiment is build up in order to correlate the structure with the emitted wavelength and orbital energy levels.


Page 43 of 43


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Highly Phosphorescent Cyclometalated Iridium(III) Complexes for

Recommend Documents