Supramolecular Structure-Dependent Thermally-Activated Delayed

Subscriber access provided by United Arab Emirates University | Libraries Deanship

Article

Supramolecular Structure Dependent Thermally Activated Delayed Fluorescence (TADF) Properties of Organic Polymorphs Yuewei Zhang, Huili Ma, Shipan Wang, Zhiqiang Li, Kaiqi Ye, Jingying Zhang, Yu Liu, Qian Peng, and Yue Wang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b05537 • Publication Date (Web): 15 Aug 2016 Downloaded from http://pubs.acs.org on August 16, 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 28

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

Supramolecular Structure Dependent Thermally Activated Delayed Fluorescence (TADF) Properties of Organic Polymorphs Yuewei Zhang,† Huili Ma,‡ Shipan Wang,† Zhiqiang Li,† Kaiqi Ye,† Jingying Zhang,† Yu Liu,*,† Qian Peng,*,# Yue Wang*,† †

State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin

University, Changchun 130012, P. R. China. ‡

Key Laboratory of Organic OptoElectronics and Molecular Engineering, Department of

Chemistry, Tsinghua University, Beijing 100084 (China). #

Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences,

Beijing 100190 (China).

ABSTRACT: The increasing demand for high performance OLEDs based on TADF principle urgently requires to establish efficient prepare strategy of high performance TADF materials. Although considerable progress has been made in molecular design approaches for TADF materials, it is still remaining unaddressed issue that how molecular aggregated states or supramolecular structures determine the TADF property of organic solids. Herein, we present an organic molecule 3-(10H-phenoxazin-10-yl)-9H-xanthen-9-one (3-PXZ-XO) with TADF and

ACS Paragon Plus Environment

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 2 of 28

polymorph characteristics. Three kinds of 3-PXZ-XO based crystals A, B and C with different TADF properties were obtained. The three crystals display obviously different emission maxima (λem,max: 535 nm for A, 555 nm for B and 576 nm for C), photoluminescence (PL) quantum yields (Φ: 51% for A, 28% for B and 39% for C) and delayed life times of excited states (τTADF: 914 ns for A, 774 ns for B and 994 ns for C). Single-crystal X-ray diffraction analyses revealed that in A, B and C there are different intermolecular π…π stacking interaction modes between the adjacent donor planes or acceptor planes. The different TADF properties of the three polymorphs are mainly attributed to their different supramolecular structures. Appropriate donor…donor and acceptor…acceptor stacking interactions induced aggregation structures can strongly enhance TADF property of organic solids.

1. INTRODUCTION Recently, the pioneering research reported by Adachi and co-workers promoted the significant progress of high performance organic light-emitting devices (OLEDs) with thermally activated delayed fluorescence (TADF) organic materials as emitters.1-10 Based on the up-conversion mechanism, the triplet excited states can transform into singlet excited states in the materials with TADF characteristic. The TADF process enables 100% of the excitons generated in OLEDs to be used for emitting light.1-4 The organic TADF materials are the potential alternative for expensive metals (such as iridium and platinum) based phosphorescent emitters that were widely used in high performance OLEDs. To achieve efficient TADF, the molecular design strategies have been proposed and performed. At molecular structure level, it was demonstrated that constructing rigid and twist D-A (donor−acceptor) structure with small overlap between HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) is a


2

Page 3 of 28

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


generally used approach to obtain TADF molecules.5-10 However, it is still an important issue that how intermolecular interactions and molecular packing modes or supramolecular structures determine the TADF property for organic solids. Understanding the relationship between supramolecular structures and TADF properties of organic solids will be of advantage to fabricating high performance OLEDs based on TADF materials. In principle, high performance can be realized by employing TADF materials as emitters or hosts in OLEDs. However, compared with phosphorescent OLEDs with excellent performance, most of TADF materials based OLEDs suffer from the serious efficiency (especially power efficiency) roll-offs up on increase of brightness. Recently, very high external quantum efficiency of 30.7% was realized at 3000 cd/m2 for some TADF systems.4 However, it is still rare that OLEDs with TADF materials as emitters display high efficiency at high brightness level (>1000 cd/m2).5-16 When TADF materials were employed as emitters in OLEDs, the doped concentration of TADF molecules must be at a relatively high level (around 5%) to satisfy the need of Dexter energy transfer (short-range electron-exchange energy transfer) from host to TADF molecules. At this doped concentration level the TADF molecules should not adopt mono-dispersed state and are in aggregated states. Therefore, the effect of aggregation or supramolecular structures on the photophysical properties of TADF molecules should be addressed. The TADF materials are also used as hosts to fabricate OLEDs.17-19 In such a case, high photoluminescent efficiency for TADF materials is not critical, while the transformation efficiency from triplet excited state to singlet excited state, nonradiative rate, carrier mobility and so on are still dominated by the supramolecular structures. In this context, elucidating the supramolecular structure-photophysical property relationship for TADF materials in solid state is urgently needed. This is a key link for establishing prepare strategies (including covalent and


3


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 4 of 28

non-covalent synthesis) of TADF materials for high performance OLEDs. In this contribution, we report the TADF molecule 3-(10H-phenoxazin-10-yl)-9H-xanthen-9-one (3-PXZ-XO) with polymorph-dependent

emission

characteristic.

The

donor…donor

(D…D)

and

acceptor…acceptor (A…A) interactions dependent TADF properties will be presented. The molecule design strategy of 3-PXZ-XO is based on the molecular structure and supramolecular interaction concepts. Xanthone (XO) was chosen as the acceptor for its small singlet-triplet splitting (∆EST) and rigid π-conjugated structure with electron-withdrawing properties.20,21 Phenoxazine (PXZ) was selected as donor for its electron-donating and steric repulsion characteristics. The integration between PXZ and XO can easily result in the formation of a twisted π-conjugated D-A structure, which can improve the intramolecular charge transfer (ICT) and effective HOMO-LUMO separation. Furthermore, some potential intermolecular interactions (such as π…π stacking and various hydrogen bonding) may exist in the solid states of this compound due to that both the donor and acceptor have planar structure feature and there are potential hydrogen bonding interaction groups. Scheme 1. Synthesis procedure of 3-PXZ-XO.

2. EXPERIMENTAL SECTION


4

Page 5 of 28

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


General. 3-PXZ-XO was synthesized by referring to the reported approach.22 All commercially available reagents were used as received unless otherwise stated. All reactions were carried out using Schlenk techniques under a nitrogen atmosphere. 1

H NMR spectra were measured on Bruker 500 MHz spectrometers with tetramethylsilane

(TMS) as the internal standard. Mass spectra were measured on an ITQ 1100 (Thermo Fisher) mass spectrometer. Elemental analyses were performed on a Vario Micro (Elementar) analyzer. The emission spectra were recorded by a Shimadzu RF-5301 PC spectrometer. The absolute fluorescence quantum yields of the crystals were measured on Edinburgh FLS920 steady state fluorimeter (excited at 345 nm). Single Crystal X-ray diffraction data were collected on a Rigaku R-AXIS-RAPID diffractometer using the ω-scan mode with graphite-monochromator Mo•Kα radiation. The structure determination was solved with direct methods using the SHELXTL programs and refined with full-matrix least squares on F2. The corresponding CCDC reference number (CCDC: 1470360 for A, 1470364 for C and 1470365 for B) and the data can be obtained free

of

charge

from

The

Cambridge

Crystallographic

Data

Centre

via

www.ccdc.cam.ac.uk/data_request/cif. Synthesis and Characterization. 3-Br-XO (3-bromo-9H-xanthen-9-one). Copper (0.20 g, 3.15 mmol), copper (I) iodide (0.20 g, 1.05 mmol), pyridine(1.6 mL, 19.7 mmol) and potassium carbonate (4.54 g, 32.9 mmol) were added to a solution of 4-bromo-2-chlorobenzoic acid (5 g, 19.7 mmol) and 4-iodophenol (9.1 g, 41.4mmol) in DMF (40 mL). The resulting solution was heated at 100 °C for 7 hours. The reaction mixture was cooled to room temperature and diluted with saturated sodium carbonate (100 mL). The mixture was washed with diethyl ether (3×100 mL). The aqueous suspension was acidified by concentrated HCl to pH = 1 and extracted with ethyl acetate (3 × 200 mL). The combined organic layers were washed with brine, 1 M sodium


5


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 28

bisulfite (aq), water and dried with sodium sulfate. After solvent removal, the crude product of aryl ether was obtained without further purification. The above product was treated with concentrated sulfuric acid (30 mL). The solution was heated at 105 °C for 1 hour. After cooled to room temperature, the reaction mixture was poured into ice-water slurry. The suspension was diluted with dichloromethane (1 L), washed with water, brine, 1N NaOH (aq), 1N NaHSO3 (aq) and water sequentially. The organic solution was dried over anhydrous Na2SO4 and organic solvent was removed to generate 3-bromo-9Hxanthen-9-one (1.27g, yield: 37%) as a white powder. 1H NMR (500 MHz, Chloroform-d): δ = 8.33 (dd, J = 8.0, 1.7 Hz, 1H), 8.21 (d, J = 8.5 Hz, 1H), 7.79 – 7.70 (m, 2H), 7.54 – 7.47 (m, 2H), 7.41 (t, J = 7.6 Hz, 1H). MS m/z: [M]+ calcd. for C13H7BrO2, 273.96; found: 274.31. 3-PXZ-XO

(3-(10H-phenoxazin-10-yl)-9H-

xanthen-9-one).

3-bromo-9H-xanthen-9-one

(411mg, 1.5 mmol), phenoxazine (411mg, 2.25 mmol), and cesium carbonate (1.13 g, 3.5 mmol) were added into dry ortho-xylene (15 mL). Then tri-tert-butylphosphine (10% in pentane, 0.58 mL, 0.24 mmol) and bis(dibenzylideneacetone)palladium (80 mg, 0.14 mmol) were added. The mixture were stirred under reflux for 12 hours. After cooling to room temperature, the mixture was extracted with dichloromethane. The combined organic layers were dried with magnesium sulfate, filtered, and evaporated under reduced pressure. The crude product was purified by column chromatography (silica, CH2Cl2 / petroleum ether = 1:1) and recrystallized from chloroform and methanol as yellow powder (381 mg, yield: 70%). 1H NMR (500 MHz, DMSOd6): δ = 8.45 (d, J = 8.4 Hz, 1H), 8.26 (dd, J = 8.0, 1.6 Hz, 1H), 7.93 (ddd, J = 8.7, 7.1, 1.7 Hz, 1H), 7.87 (d, J = 1.8 Hz, 1H), 7.71 (d, J = 8.4 Hz, 1H), 7.58 – 7.48 (m, 2H), 6.86 – 6.68 (m, 6H), 6.13 (dd, J = 7.9, 1.4 Hz, 2H). MS m/z: [M]+ calcd. for C25H15NO3, 377.11; found: 377.07. Anal.


6

Page 7 of 28

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


calcd. (%) for C25H15NO3: C, 79.56; H, 4.01; N, 3.71; O, 12.72; Found: C, 79.27; H, 4.15; N, 3.68; O, 12.90. Theoretical calculations. The DFT calculations were performed with the Gaussian 09 series of programs using the B3LYP hybrid functional and 6-31G(d, p) basis set. To obtain the vertical emission energies, time-dependent DFT (TD-DFT) calculations were performed to evaluate the lowest singlet (S1) based on the S1 geometries, the triplet (T1) states of the polymorphs were then calculated. All these above calculations were carried out at the B3LYP/6-31G(d, p) level with the Gaussian 09 package. In order to investigate the cases in crystal state, we carried out the calculations by using the combined quantum mechanics and molecular mechanics (QM/MM) method with two-layer ONIOM method.23 And the B3LYP functional and the 6-31G (d) basis set were adopted for the quantum mechanics calculations. The computational models (Figure S1) were built from X-ray diffractions crystal structure, a cluster of 54 molecules for crystal A, 50 molecules for crystal B, and 84 molecules for crystal C. The central molecule was chosen as QM molecule and set as the high layer, whereas the remaining molecules around were treated as the MM molecules and defined as the low layer. The universal force field (UFF) was used for the MM part, and the molecules of MM part were frozen during the QM/MM geometry optimizations.24 The electronic embedding are adopted in QM/MM calculations by incorporating the partial charges of the MM region into the quantum mechanical Hamiltonian.25 All the calculations were carried out by using Gaussian 09 program.26 3. RESULTS AND DISCUSSION Synthesis and photophysical properties. The synthesis of 3-PXZ-XO (Scheme 1) was achieved by Ullmann coupling reaction between the XO and PXZ moieties with high yields


7


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 8 of 28

(70%). The DFT-calculations show that the HOMO orbital is mainly dispersed over the PXZ moiety and part of the adjacent phenyl bridge, while the LUMO orbital mainly situates on the XO moiety (Figure 1). This kind of molecular orbital distribution not only ensures a small ∆EST of 0.040 eV, which was calculated based on low temperature spectroscopic data in Figure 2a, but also a large radiative rate constant (kF) caused by the partial orbital overlap between HOMO and LUMO (Table 1). For 3-PXZ-XO toluene solution, the photoluminescence (PL) quantum yields (Φ) and excited state lifetimes (τ) recorded under different conditions (air and nitrogen) revealed that oxygen resulted in obvious decrease of Φ and reduction of τ (Figures 2b, 3a, S2, and S3). Therefore, 3-PXZ-XO molecules have a typical TADF feature.5 Under nitrogen atmosphere the component of long life excited states (τ = 398 ns) is 22.5% and that of short life ones (τ = 25.5 ns) is 77.5%.

Figure 1. Calculated spatial distributions of the HOMO and LUMO energy densities of 3-PXZXO.


8

Page 9 of 28

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 2. (a) Emission spectra of 3-PXZ-XO in toluene at 77 K (black) and at 77 K with a 10 ms delay (red). (b) Emission spectra of 3-PXZ-XO in toluene recorded at room temperature under air (red) and nitrogen (black) atmosphere. It is well known that in the solid states, the photophysical properties of organic materials are strongly dependent on the molecular arrangement.27-33 In order to understand the structure-TADF property relationship in solid states, the various polymorphs based on 3-PXZ-XO molecule have been successfully prepared and investigated by PL spectroscopy and single crystal X-ray diffraction. Crystal A was prepared by layering equal amount of water onto the tetrahydrofuran (THF) solution (~10-3mol/L) at the temperature of 273 K (±3 K). Vacuum thermal sublimation and deposition of 3-PXZ-XO powder or slow evaporation of its saturated THF solution at room temperature resulted in the formation of crystal B. Crystal C was generated from the mixture solvent system of THF/water (1:1 of V to V) at room temperature. As shown in Figure 4, the emission band of crystal A (λmax,em = 535 nm) lies in the green region with a Φ value of 51%, while crystals B (λmax,em = 555 nm, Φ = 28%) and C (λmax,em = 576 nm, Φ = 39%) display the red-shifted emissions with yellow-green and orange colours, respectively. The PL quantum yields of crystals A and C are remarkably higher than that of solution phase (Φ = 26%) suggesting that in crystalline states some molecular vibration induced emission quenching were efficiently suppressed due to the intermolecular interaction confinements. The aggregations resulted in obvious enhancement of TADF for crystals A and C. This phenomenon should be attributed into a unique aggregation enhanced emission (AEE) behaviour.34-36 The time resolution PL spectroscopic measurements (Figures 3b-3d, S4-S6) revealed that in air all three crystals possess long time excited states with life times of 914 ns for A, 774 ns for B and 994 ns for C, respectively. Notably, the long-time components are 27.16% for A, 32.85% for B and


9


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 28

76.65% for C, respectively, which are larger than that (22.5%) for 3-PXZ-XO toluene solution under nitrogen atmosphere. To confirm that the delayed fluorescence in the crystal state originated from TADF, temperature-dependent transient photoluminescent decay was recorded from 100 to 300 K (Figures S7-S9). The ratio of delayed component increased with the temperature rising from 100 to 300 K, suggesting the behavior of thermal activation energy for TADF. Especially, the long-lived exited state and TADF characteristic are dominant in crystal C. Therefore, crystal C is the best solid for TADF emission.

Figure 3. (a) Comparison of the time-resolved PL traces of 3-PXZ-XO in toluene (λex = 345 nm) at room temperature under air (red) and N2 (black) atmospheres. Inset: The fluorescence quantum yields and lifetimes of the prompt/delayed component; Transient decay spectra of crystals A (b), B (c) and C (d). Inset: Proportion of the integrated area of prompt (fluorescent) and delayed (TADF) component.


10

Page 11 of 28

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 fluorescent (ФF) and TADF (ФTADF) quantum yields could be got by comparing the proportion of the integrated intensity of each component to the total Ф in the transient photoluminescence. The intensity ratio between prompt (r1) and delayed (r2) components were determined as reported literature using emission life time (τ1, τ2) and fitting parameter (Α1, Α2).37 According to the reported approach,5,10,38 the rate constants of fluorescent (kF), internal conversion (kIC), TADF (kTADF), intersystem crossing (kISC), reverse intersystem crossing (kRISC) as well as the efficiency of ISC (ΦISC), RISC (ΦRISC) can be given by the following formulas 1-6 in the crystal state. Φ = kF / (kF + kIC)

(1)

ΦF = kF / (kF + kIC + kISC) = kF × τF

(2)

ΦISC = kISC / (kF + kIC + kISC)

(3)

ΦTADF / ΦF = (ΦISC × ΦRISC) / (1- ΦISC × ΦRISC)

(4)

kTADF = ΦTADF / (ΦISC × τTADF)

(5)

kRISC = kF × kTADF × ΦTADF / (kISC × ΦF)

(6)

And we estimated the ∆EST of these molecules in the crystal state at room temperature by using an approximate relationship among ∆EST, kTADF and kF as follows: kTADF = 1/3kF exp(−∆EST/RT)

(7)

where R and T denote the ideal gas constant and room temperature (298.15 K), respectively. The photophysical parameters that were calculated according to the above formulas for the polymorphs were summarized in Table 1. For all of three crystals, the reverse intersystem


11


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 28

transformation efficiencies (ФRISC) are as high as 99.60% for A, 99.97% for B and 100.00% for C, respectively. Upon assembling into different crystalline phases, the 3-PXZ-XO molecules not only exhibited different TADF properties compared with its solution phase, but also polymorph dependent TADF feature. Compared with the normal TADF materials the delayed life times of the crystals in this study are remarkably shorter, which may reduce the triplet−triplet annihilation (TTA), singlet−triplet annihilation (STA), and triplet−polaron annihilation (TPA).7,10,39,40 It's worth to note that for 3-PXZ-XO solution the ∆Est (0.036 eV) value that estimated form equation (7) is near to the one (0.040 eV) calculated based on low temperature emission spectra (Figure 2a). Although the ∆Est (0.047 eV) of crystal A is even longer than that in solution (0.036 eV), crystal A exhibited stronger TADF. A rational explanation for this behavior is that according to equation (4) ΦTADF is not only proportional to ΦRISC, which is determined by ∆EST, but also to ΦISC and ΦF. Compared with solution state, crystal A have much larger ΦF. In crystal state, the intermolecular interactions can efficiently suppress the molecular vibration that is the most important origin of non-radiative decay.


12

Page 13 of 28

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 4. Normalized fluorescence spectra of polymorphs A, B and C at room temperature; the above inset: photo images of the polymorphs under 365 nm UV irradiation at room temperature. Table 1. TADF-related data for crystals A, B, C and solution (S) at room temperature a λem,maxb

Фc

ФFd

τFe

τTADFf

kFg

kICh

kISCi

kTADFj

kRISCk

ФISCl

ФRISCm

∆EST

(nm)

(%)

(%)

(ns)

(ns)

(107 s-1)

(107 s-1)

(107 s-1)

(107 s-1)

(107 s-1)

(%)

(%)

(eV)

A

535

51

37.15

35.1

914

1.06

1.02

0.78

0.056

0.028

27.27

99.60

0.047

B

555

28

18.80

47.4

774

0.40

1.03

0.70

0.036

0.010

32.86

99.97

0.034

C

576

39

9.11

53.8

994

0.17

0.27

1.44

0.039

0.015

76.60

100.00

0.010

S

559

26

20.15

25.5

398

0.79

2.25

0.88

0.065

0.017

22.50

99.91

0.036

a

All the related experiments were performed in the air atmosphere at room temperature; S means the toluene solution under N2 atmosphere. bEmission maxima. cThe total fluorescence quantum yield. dThe prompt fluorescent (ФF) component of Φ. e,fThe lifetimes of prompt fluorescent (τF) and TADF (τTADF). g-kThe rate constants of fluorescent (kF), internal conversion (kIC), TADF (kTADF), intersystem crossing (kISC) and reverse intersystem crossing (kRISC). l,mThe efficiency of ISC (ΦISC), RISC (ΦRISC).


13


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 28

Molecular Structures of A, B and C. To figure out the relationship between TADF properties and structures, the close investigations of molecular and supramolecular structures of the three crystals have been performed. The single-crystal X-ray diffraction analyses demonstrated that both the PXZ and XO moieties display perfect planar π-conjugated structure feature for all of three crystals. In three polymorphs the 3-PXZ-XO molecules adopt highly twisted structural characteristic with the dihedral angles of 71.13°, 75.92°, 86.79° for crystals A, B and C, respectively, between the donor and acceptor planes (Figure 5). The largest delayed fluorescence component (76.65%) for C should be mainly attributed to the largest dihedral angle between donor and acceptor planes. It is well known that the energy gap ∆EST is mainly determined by the separation of the HOMO and LUMO. In other words, the molecular conformation plays a dominant role in determining the ∆EST value.41,42 So, the crystal C with most twisted structure possesses the smallest ∆EST. According to the variation tendency of dihedral angles, the emission maxima of the three crystals might follow the order of A > B > C. It was demonstrated that smaller dihedral angles between the donor and acceptor moieties can lead to larger π-conjugated degree, smaller band gap and the red-shift emission maximum.43 However, the experimental results presented the completely contrary order. Above deduction is based on the principle of molecular structure-property relationship, while supramolecular structure-property relationship has not been considered.

Figure 5. Molecular structures of crystals A (a), B (b), C (c).


14

Page 15 of 28

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 6. Molecular packing modes of 3-PXZ-XO in the single crystals of A (a), B (b), C (c). Supramolecular structures and luminescent properties. The supramolecular structures of the crystals are illustrated in Figures 6 and 7. The common structure feature of the A, B and C is that the crystals are formed based on intermolecular π…π interactions accompanied with intermolecular non-covalent bonds such as C−H···O, O=C···H-C and C-H···π, which can efficiently depress the molecular vibrations and enhance the emission intensity. Therefore, the


15


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 28

crystals exhibited higher PL efficiencies than the solution of 3-PXZ-XO.44-47 In crystals A and C, the dominant non-covalent bonds are intermolecular π…π interactions between donor and donor aromatic planes (PXZ). The π…π stacking modes of PXZ donors in A and C are different from each other. For crystal A, the PXZ dimers with contact distance of 3.42 Å and overlapping area of around 50% adopt the side-slipping stacking mode along the long and short axes of PXZ plane, simultaneously. In addition, there are very weak π…π stacking interaction between C=O and XO plane within crystal A. For crystal C, the PXZ dimers with contact distance of 3.39 Å and overlapping area of around 50% display the side-slipping stacking mode along the short axis of PXZ plane only. In crystal B, the most obvious non-covalent interactions are the π…π stacking interaction between XO acceptor groups and the interplanar separation and overlapping area are 3.48 Å and approximate 65%, respectively. For the three crystals, a remarkably identical supramolecular structure feature is that based on stronger π…π stacking interactions the 3-PXZ-XO molecules firstly aggregated into dimers, then assembled into crystals through weaker interactions of C−H···O, O=C···H−C and C−H···π. The formation of π…π stacking induced dimers should result in the generation of excimer exited states. Therefore, the three crystals exhibit obviously longer prompt and delayed fluorescence life times compared with 3-PXZ-XO solution (Figure 3). The intermolecular π…π stacking interactions (including donor…donor and acceptor…acceptor interactions) can lengthen the life times of singlet and triplet excited states, which is beneficial for intersystem and reverse intersystem crossing processes. The high efficiency of reverse intersystem crossing process is the prerequisite to achieve desired TADF efficiency. Therefore, appropriate π…π stacking overlapping can promote the TADF process. The crystals A and C showed significantly longer delayed life time compared with crystal B suggesting that the donor…donor stacking can largely


16

Page 17 of 28

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


lengthen the life times of triplet excited states compared with acceptor…acceptor stacking for 3PXZ-XO system. The crystal B displayed lower Φ compared with crystals A and C indicating that stronger acceptor…acceptor stacking interaction can result in certain emission quenching.

Figure 7. Molecular stacking modes for the dimers in crystals A (a), B (b) and C (c). The crystals A and C exhibit obviously different Φ values, emission maxima and delayed fluorescence ratios, which is ascribed to their different donor…donor stacking modes in molecular dimers. Furthermore, in the crystal A the molecular dimers adopt only one orientation, while in crystal C the molecular dimers take over two kinds of orientations. In the other words, in crystal C the molecules or molecular dimers are more disordered than that in crystal A. Meanwhile, in crystal C the π…π stacking distance is shorter than that in crystal A, which can result in the red-shift of emission.48-50 The different photophysical properties between crystals A and C should be ascribed to their different non-covalent interaction modes and molecular


17


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 28

arrangement characteristics. It was demonstrated that the change of organic luminescent solids from ordered crystalline phase to disordered amorphous phase could result in the decrease of Φ and red-shift of emission maxima.51-53 In crystal B, the molecular dimers also adopt only one orientation and its emission maximum is smaller than that of crystal C. The donor…donor stacking mode and three dimension molecular arrangement architecture in C are more conducive to achieve lager torsion angle between donor and acceptor aromatic planes, small ∆EST and strong TADF. It is worth to note that the strongly twisted donor-acceptor structure feature in crystal C should be attributed to the special molecular packing and intermolecular non-covalent interactions. Table 2. The adiabatic excitation of S1 and T1, the reorganization energies and the energy gap between S1 and T1 in crystals A, B and C.

S1a[eV]

T1b[eV]

λgc [eV]

λed[eV]

∆EST[eV]

A

1.806

1.795

0.226

0.293

0.011

B

1.799

1.787

0.199

0.293

0.012

C

1.773

1.766

0.202

0.239

0.007

a,b

S1 is the singlet excitation energy of 3-PXZ-XO, T1 is the triplet excitation energy of 3-PXZ-XO. c,dIn the process of S1 to S0 transition, λg represents the relaxation energy at the potential energy surface of the S0 state, λe represents the relaxation energy at the potential energy surface of S1 state.

Theoretical calculations for crystals A, B and C. To further understand the photophysical properties of crystals A, B and C, the theoretical calculations based on their different assembly structures have been performed by using the combined quantum mechanics and molecular mechanics (QM/MM) method with B3LYP/6-31G(d) functional and universal force field (UFF) (Figure S1). The optimized torsion angles around the four atoms of 1, 2, 3 and 4 (Figure S10) are


18

Page 19 of 28

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


72.09° for A, 75.07° for B and 89.00° for C, respectively, which display similar variation regulation to the experimental values (72.89° for A, 82.35° for B and 89.45° for C). The calculated transition properties are summarized in Table 2. All of three crystals displayed quite smaller relaxation energies (variation from 0.193 to 0.293 eV) for S0 and S1 states, which are similar to the values of the reported high performance TADF materials.5 Therefore, in the crystals A, B and C the molecular torsion vibrations were efficiently confined by the intermolecular interactions such as π…π stacking, C−H···O, O=C···H-C and C-H···π noncovalent bonds, which can significantly depress non-radiative decay and reduce relaxation energies. The crystal C presents the smallest theoretically calculated ∆EST (0.007 eV), which is consistent with experimental results. 4. CONCLUSIONS In summary, a TADF molecule 3-PXZ-XO with polymorph property was designed and synthesized. Three kinds of 3-PXZ-XO based crystals A, B and C with obviously different TADF properties were successfully prepared. The study of supramolecular structure-TADF property relationship demonstrated that appropriate non-covalent interactions and aggregation architecture can enhance the TADF property. Both the donor…donor and acceptor…acceptor πstacking interactions can lengthen the life times for singlet and triplet excited states and then promote the TADF process. Furthermore, donor…donor π-stacking interaction is more efficient for enhancing TADF than acceptor…acceptor π…π stacking interaction for 3-PXZ-XO based crystals. The comparison between the crystals A and C revealed that the disordered molecular arrangement and strong π…π stacking can improve the delayed fluorescent component, but result in the decrease of PL efficiency. The distinguished intermolecular non-covalent interactions resulted in variable molecular conformations with different torsion angles between donor and


19


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 28

acceptor planes. The desired molecular conformations, which are beneficial to the improvement of TADF property, can be achieved by optimizing the supramolecular structure. To approach high performance TADF materials, the molecular packing regulation is equally important with the molecular structure optimization and the efficient combination of them can generate efficient TADF materials. ASSOCIATED CONTENT Supporting Information. The computational geometries of the investigated compound/crystals; spectral characterization data; complete crystallographic data (CIF files) of polymorphs A, B and C. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (Y. Liu), [email protected] (Q. Peng) and [email protected] (Y. Wang); Tel: +86-431-85168484. Notes The authors declare no competing financial interests. ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (91333201 and 21473214), National Basic Research Program of China (2015CB65500) and Program for Chang Jiang Scholars and Innovative Research Team in University (No. IRT101713018).

REFERENCES


20

Page 21 of 28

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


(1) Nakanotani, H.; Higuchi, T.; Furukawa, T.; Masui, K.; Morimoto1, K.; Numata, M.; Tanaka, H.; Sagara, Y.; Yasuda, T.; Adachi, C. High-efficiency Organic Light-Emitting Diodes with Fluorescent Emitters. Nat. Commun. 2014, 5, 4016–4022. (2) Lee, S. Y.; Yasuda, T.; Yang, Y. S.; Zhang, Q.; Adachi, C. Luminous Butterflies: Efficient Exciton Harvesting by Benzophenone Derivatives for Full-Color Delayed Fluorescence OLEDs. Angew. Chem. Int. Ed. 2014, 53, 6402–6406; Angew. Chem. 2014, 126, 6520–6524. (3) Hirata, S.; Sakai, Y.; Masui, K.; Tanaka, H.; Lee, S. Y.; Nomura, H.; Nakamura, N.; Yasumatsu, M.; Nakanotani, H.; Zhang, Q.; Shizu, K.; Miyazaki, H.; Adachi, C. Highly Efficient Blue Electroluminescence Based on Thermally Activated Delayed Fluorescence. Nat. Mater. 2015, 14, 330–336. (4) Kaji, H.; Suzuki, H.; Fukushima, T.; Shizu, K.; Kubo, S.; Komino, T.; Oiwa, H.; Suzuki, F.; Wakamiya, A. Murata, Y.; Adachi. C. Purely Organic Electroluminescent Mmaterial Realizing 100% Conversion from Electricity to Light. Nat. Commun. 2015, 6, 8476–8484. (5) Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C. Highly Efficient Organic Light-Emitting Diodes from Delayed Fluorescence. Nature, 2012, 492, 234–238. (6) Zhang, Q.; Li, J.; Shizu, K.; Huang, S.; Hirata, S.; Miyazaki, H.; Adachi, C. Design of Efficient Thermally Activated Delayed Fluorescence Materials for Pure Blue Organic Light Emitting Diodes. J. Am. Chem. Soc. 2012, 134, 14706–14709. (7) Zhang, Q.; Li, B.; Huang, S.; Nomura, H.; Tanaka, H.; Adachi, C. Efficient Blue Organic Light-Emitting Diodes Employing Thermally Activated Delayed Fluorescence. Nat. Photon. 2014, 8, 326–332. (8) Tanaka, H.; Shizu, K.; Naka-notani, H.; Adachi, C. Twisted Intramolecular Charge Transfer State for Long-Wavelength Thermally Activated Delayed Fluorescence. Chem. Mater. 2013, 25, 3766–3771. (9) Shizu, K.; Tanaka, H.; Uejima, M.; Sato, T.; Tanaka, K.; Kaji, H.; Adachi, C. Strategy for Designing Electron Donors for Thermally Activated Delayed Fluorescence Emitters. J. Phys. Chem. C 2015, 119, 1291.


21


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 28

(10) Zhang, Q.; Kuwabara, H.; Potscavage, W. J.; Huang, S.; Hatae, Y.; Shibata, T.; Adachi, C. Anthraquinone-Based Intramolecular Charge-Transfer Compounds: Computational Molecular Design,

Thermally

Activated

Delayed

Fluorescence,

and

Highly

Efficient

Red

Electroluminescence. J. Am. Chem. Soc. 2014, 136, 18070–18081. (11) Tanaka, H.; Shizu, K.; Miyazaki, H.; Adachi, C. Efficient Green Efficient Green Thermally Activated Delayed Fluorescence (TADF) from a Phenoxazine–triphenyltriazine (PXZ–TRZ) Derivative. Chem. Commun. 2012, 48, 11392–11394. (12) Wang, H.; Xie, L.; Peng, Q.; Meng, L.; Wang, Y.; Yi, Y.; Wang, P. Novel Thermally Activated Delayed Fluorescence Materials–Thioxanthone Derivatives and Their Applications for Highly Efficient OLEDs. Adv. Mater. 2014, 26, 5198–5204. (13) Kawasumi, K.; Wu, T.; Zhu, T.; Chae, H. S.; Voorhis, T. V.; Baldo, M. A.; Swager, T. M. Thermally Activated Delayed Fluorescence Materials Based on Homoconjugation Effect of Donor–Acceptor Triptycenes. J. Am. Chem. Soc. 2015, 137, 11908-11911. (14) Lee, D. R.; Kim, M. S.; Jeon, K.; Hwang, S.; Lee, C. W.; Lee, J. Y. Design Strategy for 25% External Quantum Efficiency in Green and Blue Thermally Activated Delayed Fluorescent Devices. Adv. Mater. 2015, 27, 5861–5867. (15) Wang, S.; Yan, X.; Cheng, Z.; Zhang, H.; Liu, Y.; Wang, Y. Highly Efficient NearInfrared Delayed Fluorescence Organic Light Emitting Diodes Using a Phenanthrene-Based Charge-Transfer Compound. Angew. Chem. Int. Ed. 2015, 54, 13068–13072. (16) Rajamalli, P.; Senthilkumar, N.; Gandeepan, P.; Ren-Wu, Z.; Lin, W.; Cheng, H. A Thermally Activated Delayed Blue Fluorescent Emitter with Reversible Externally Tunable Emission. J. Mater. Chem. C. 2016, 4, 900–904. (17) Zhang, D. D.; Duan, L.; Li, C.; Li, Y. L.; Li, H. Y.; Zhang, D. Q.; Qiu, Y. HighEfficiency Fluorescent Organic Light-Emitting Devices Using Sensitizing Hosts with a Small Singlet–Triplet Exchange Energy. Adv. Mater. 2014, 26, 5050–5055. (18) Wang, H.; Meng, L.; Shen, X.; Wei, X.; Zheng, X.; Lv, X.; Yi, Y.; Wang, Y.; Wang, P. Highly Efficient Orange and Red Phosphorescent Organic Light-Emitting Diodes with Low


22

Page 23 of 28

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


Roll-Off of Efficiency using a Novel Thermally Activated Delayed Fluorescence Material as Host. Adv. Mater. 2015, 27, 4041–4047. (19) Wang. S.; Zhang, Y.; Chen, W.; Wei, J.; Liu, Y.; Wang, Y. Achieving High Power Efficiency and Low Roll-Off OLEDs Based on Energy Transfer from Thermally Activated Delayed Excitons to Fluorescent Dopants. Chem. Commun. 2015, 51, 11972–11975. (20) Pownall, H. J.; Huber, J. R. Absorption and Emission Spectra of Aromatic Ketones and their Medium Dependence. Excited States of Xanthone. J. Am. Chem. Soc. 1971, 93, 6429–6436. (21) Constapel, V. R.; Etinski, M.; Marian, C. M. Photophysics of Xanthone: A Quantum Chemical Perusal. J. Phys. Chem. A 2013, 117, 3935−3944. (22) Li, L.; Zhong, M. Tricyclic Fused Ring Inhibitors Of Hepatitis, CPCT, US, 2011, 053759. (23) Morokuma, K.; Wang Q.; Vreven, T. Performance Evaluation of the Three-Layer ONIOM Method: Case Study for a Zwitterionic Peptide. J. Chem. Theory Comput. 2006, 2, 1317–1324. (24) Mayhall, N. J.; Raghavachari, K.; Hratchian, H. P. ONIOM-Based QM:QM Electronic Embedding Method Using Löwdin Atomic Charges: Energies and Analytic Gradients. J. Chem. Phys. 2010, 132, 114107. (25) Lundberg, M.; Kawatsu, T.; Vreven, T.; Frisch, M. J.; Morokuma, K. Transition States in a Protein Environment − ONIOM QM:MM Modeling of Isopenicillin N Synthesis. J. Chem. Theory Comput. 2008, 5, 222–234. (26) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A., et al. Gaussian 09, Revision D.01 ed.; Gaussian, Inc.: Wallingford, CT, 2013. (27) Dong, J.; Solntsev, K. M.; Tolbert, L. M. Activation and Tuning of Green Fluorescent Protein Chromophore Emission by Alkyl Substituent-Mediated Crystal Packing. J. Am. Chem. Soc. 2009, 131, 662–670.


23


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 28

(28) Babu, S. S.; Kartha, K. K.; Ajayaghosh, A. Excited State Processes in Linear π-SystemBased Organogels. J. Phys.Chem. Lett. 2010, 1, 3413–3424. (29) Zhang, G.; Lu, J.; Sabat, M.; Fraser, C. L. Polymorphism and Reversible Mechanochromic Luminescence for Solid-State Difluoroboron Avobenzone. J. Am. Chem. Soc. 2010, 132, 2160−2162. (30) Yoon, S. J.; Chung, J. W.; Gierschner, J.; Kim, K. S.; Choi, M. G.; Kim, D.; Park, S. Y. Multistimuli Two-Color Luminescence Switching via Different Slip-Stacking of Highly Fluorescent Molecular Sheets. J. Am. Chem. Soc. 2010, 132, 13675– 13683. (31) Dou, C.; Han, L.; Zhao, S.; Zhang, H.; Wang, Y. Multi-Stimuli-Responsive Fluorescence Switching of a Donor-Acceptor π-Conjugated Compound. J. Phys. Chem. Lett. 2011, 2, 666– 670. (32) Dong, B.; Wang, M.; Xu, C.; Feng, Q.; Wang, Y. Tuning Solid-State Fluorescence of a Twisted π-Conjugated Molecule by Regulating the Arrangement of Anthracene Fluorophores. Cryst. Growth Des. 2012, 12, 5986−5993. (33) Gierschner, J.; Lüer, L.; Milián-Medina, B.; Oelkrug, D.; Egelhaaf, H.-J. Highly Emissive H-Aggregates or Aggregation-Induced Emission Quenching? The Photophysics of All-Trans para-Distyrylbenzene. J. Phys. Chem. Lett. 2013, 4, 2686−2697. (34) Zhang, X. Q.; Chi, Z. G.; Zhou, X.; Liu, S. W.; Zhang, Y.; Xu, J. R. Influence of Carbazolyl Groups on Properties of Piezofluorochromic Aggregation-Enhanced Emission Compounds Containing Distyrylanthracene. J. Phys. Chem. C 2012, 116, 23629. (35) Yuan, H.; Wang, K.; Yang, K.; Liu, B.; Zou, B. Luminescence Properties of Compressed Tetraphenylethene: the Role of Intermolecular Interactions J. Phys. Chem. Lett. 2014, 5, 2968– 2973. (36) Dong, Y. Q.; Lam, J. W. Y.; Tang, B. Z. Mechanochromic Luminescence of AggregationInduced Emission Luminogens. J. Phys. Chem. Lett. 2015, 6, 3429-3436.


24

Page 25 of 28

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


(37). Nakagawa, T.; Ku, S. Y.; Wong, K. T.; Adachi, C. Electroluminescence Based on Thermally Activated Delayed Fluorescence Generated by a Spirobifluorene Donor–Acceptor Structure. Chem. Commun. 2012, 48, 9580. (38) Tao, Y.; Yuan, K.; Chen, T.; Xu, P.; Li, H.; Chen, R.; Zheng, C.; Zhang, L.; Huang, W. Thermally Activated Delayed Fluorescence Materials Towards the Breakthrough of Organoelectronics. Adv. Mater. 2014, 26, 7931−7958. (39) Baldo, M. A.; Adachi, C.; Forrest, S. R. Transient Analysis of Organic Electrophosphorescence. II. Transient Analysis of Triplet-Triplet Annihilation. Phys. Rev. B 2000, 62, 10967. (40) Song, D.; Zhao, S.; Luo, Y.; Aziz, H. Causes of Efficiency Roll-Off in Phosphorescent Organic Light Emitting Devices: Triplet-Triplet Annihilation versus Triplet-Polaron Quenching. Appl. Phys. Lett. 2010, 97, 243304. (41) Leitl, M. J.; Krylova, V. A.; Djurovich, P. I.; Thompson, M. E.; Yer-sin, H. Phosphorescence versus Thermally Activated Delayed Fluorescence. Controlling Singlet–Triplet Splitting in Brightly Emitting and Sublimable Cu(I) Compounds. J. Am. Chem. Soc. 2014, 136, 16032−16038. (42) Chen, X.; Zhang, S.; Fan, J.; Ren, A. Nature of Highly Efficient Thermally Activated Delayed Fluorescence in Organic Light-Emitting Diode Emitters: Nonadiabatic Effect between Excited States. J. Phys. Chem. C 2015, 119, 9728−9733. (43) Wang, K.; Zhang, H.; Chen, S.; Yang, G.; Zhang, J.; Tian, W.; Su, Z.; Wang, Y. Organic Polymorphs: One-Compound-Based Crystals with Molecular-Conformation- and PackingDependent Luminescent Properties. Adv. Mater. 2014, 26, 6186–6173. (44) Liu, Y.; Tao, X.; Wang, F.; Shi, J.; Sun, J.; Yu, W.; Ren, Y.; Zou, D.; Jiang, M. Intermolecular Hydrogen Bonds Induce Highly Emissive Excimers: Enhancement of Solid-State Luminescence. J. Phys. Chem. C 2007, 111, 6544–6549. (45) Xu, S.; Liu, T.; Mu, Y.; Wang, Y.; Chi, Z.; Lo, C.; Liu, S.; Zhang, Y.; Lien, A.; Xu, J. White-Light Emission Strategy of a Single Organic Compound with Aggregation-Induced


25


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 28

Emission and Delayed Fluorescence Properties. Angew. Chem. Int. Ed. 2015, 54, 874–878; Angew. Chem. 2015, 127, 888–892. (46) Yoshi, R.; Hirose, A.; Tanaka, K.; Chujo, Y. Functionalization of Boron Diiminates with Unique Optical Properties: Multicolor Tuning of Crystallization-Induced Emission and Introduction into the Main Chain of Conjugated Polymers. J. Am. Chem. Soc. 2014, 136, 18131– 18139. (47) Gong, Y.; Chen, G.; Peng, Q.; Yuan, W. Z.; Xie, Y.; Li, S.; Zhang, Y.; Tang, B. Z. Achieving Persistent Room Temperature Phosphorescence and Remarkable Mechanochromism from Pure Organic Luminogens. Adv. Mater. 2015, 27, 6195–6201. (48) Zhang, H. Y., Zhang, Z. L., Ye, K. Q., Zhang, J. Y. and Wang, Y. Organic Crystals with Tunable Emission Colors Based on a Single Organic Molecule and Different Molecular Packing Structures. Adv. Mater. 2006, 18, 28369– 2372. (49) Zhang, Z.; Zhang, Y.; Yao, D.; Bi, H.; Javed, I.; Fan, Y.; Zhang, H.; Wang, Y. Anthracene-Arrangement-Dependent Emissions of Crystals of 9-Anthrylpyrazole Derivatives. Cryst. Growth Des. 2009, 9, 5069–5076. (50) Dong, Y.; Xu, B.; Zhang, J.; Tan, X.; Wang, L.; Chen, j.; Lv, H.; Wen, S.; Li, B.; Ye, L.; Zou, B.; Tian, W. Piezochromic Luminescence Based on the Molecular Aggregation of 9,10Bis((E)-2-(pyrid-2-yl)vinyl)anthracene. Angew. Chem. Int. Ed. 2012, 51, 10782; Angew. Chem. 2012, 124, 10940. (51) Gu, X.; Yao, J.; Zhang, G.; Yan, Y.; Zhang, C.; Peng, Q.; Liao, Q.; Wu, Y.; Xu, Z.; Zhao, Y.; Fu, H.; Zhang, D. Polymorphism-Dependent Emission for Di(p- methoxylphenyl)dibenzofulv ene and Analogues: Optical Waveguide/Amplified Spontaneous Emission Behaviors. Adv. Funct. Mater. 2012, 22, 4862–4872. (52) Li, R.; Xiao, S.; Li, Y.; Lin, Q.; Zhang, R.; Zhao, J.; Yang, C.; Zou, K.; Li, D.; Yi, T. Polymorphism-Dependent and Piezochromic Luminescence Based on Molecular Packing of a Conjugated Molecule. Chem. Sci. 2014, 5, 3922–3928.


26

Page 27 of 28

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


(53) Galer, P.; Korošec, R. C.; Vidmar, M.; Šket, B. Crystal Structures and Emission Properties of the BF2 Complex 1-Phenyl-3-(3,5-dimethoxyphenyl)-propane-1,3-dione: Multiple Chromisms, Aggregation- or Crystallization-Induced Emission, and the Self-Assembly Effect. J. Am. Chem. Soc. 2014, 136, 7383–7394.


27


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 28

Table of Contents Graphic


28

Supramolecular Structure-Dependent Thermally-Activated Delayed

Recommend Documents