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Heteroleptic Copper(I) Pseudorotaxanes Incorporating Macrocyclic Phenanthroline Ligands of Different Sizes Meera Mohankumar, Michel Holler, Eric Meichsner, Jean-François Nierengarten, Frédéric Niess, Jean-Pierre Sauvage, Béatrice Delavaux-Nicot, Enrico Leoni, Filippo Monti, Joanna M. Malicka, Massimo Cocchi, Elisa Bandini, and Nicola Armaroli J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 03 Jan 2018 Downloaded from http://pubs.acs.org on January 3, 2018

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Journal of the American Chemical Society

Heteroleptic Copper(I) Pseudorotaxanes Incorporating Macrocyclic Phenanthroline Ligands of Different Sizes. Meera Mohankumar,◊ Michel Holler,◊ Eric Meichsner,◊ Jean-François Nierengarten,◊* Frédéric Niess,§ Jean-Pierre Sauvage,§* Béatrice Delavaux-Nicot,‡* Enrico Leoni,†¶ Filippo Monti,† Joanna M. Malicka,∞ Massimo Cocchi,† Elisa Bandini,† Nicola Armaroli†* ◊

Laboratoire de Chimie des Matériaux Moléculaires, Université de Strasbourg et CNRS (UMR7509), ECPM, 67087 Strasbourg Cedex 2, France; §

Institut de Science et Ingénierie Supramoléculaires, Université de Strasbourg, 8 allée Gaspard Monge, 67000 Strasbourg, France;

‡

Laboratoire de Chimie de Coordination du CNRS (UPR 8241), Université de Toulouse (UPS, INPT), 205 Route de Narbonne, 31077 Toulouse Cedex 4, France; †

Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy; ¶

Laboratorio Tecnologie dei Materiali Faenza, ENEA, Via Ravegnana 186, 48018 Faenza (RA), Italy;

∞

Laboratorio MIST E-R, Via P. Gobetti 101, 40129 Bologna, Italy

ABSTRACT: A series of copper(I) pseudorotaxanes has been prepared from bis[2-(diphenylphosphino)phenyl] ether and macrocyclic phenanthroline ligands with different ring sizes (m30, m37 and m42). Variable temperature studies carried out on the resulting [Cu(mXX)(POP)]+ (mXX = m30, m37 and m42) derivatives have revealed a dynamic conformational equilibrium due to the folding of the macrocyclic ligand. The absorption and luminescence properties of the pseudorotaxanes have been investigated in CH2Cl2. They exhibit metal-to-ligand-charge-transfer (MLCT) emission with photoluminescence quantum yields (PLQYs) in the range 20-30%. The smallest system [Cu(m30)(POP)]+ shows minimal differences in spectral shape and position compared to its analogues, suggesting a slightly distorted coordination environment. PLQY is substantially enhanced in PMMA films (≈ 50-60%). The study of emission spectra and excited state lifetimes in powder samples as a function of temperature (78-338 K) reveals thermally activated delayed fluorescence (TADF), with sizeable differences in the singlet-triplet energy gap compared to the reference compound [Cu(dmp)(POP)]+ (dmp = 2,9dimethyl-1,10-phenanthroline) and within the pseudorotaxane series. The system with the largest ring ([Cu(m42)(POP)]+) has been tested as emissive material in OLEDs and affords bright green devices with higher luminance and greater stability compared to [Cu(dmp)(POP)]+, which lacks the macrocyclic ring. This highlights the importance of structural factors in the stability of electroluminescent devices based on Cu(I) materials.

INTRODUCTION Owing to a peculiar combination of electronic and structural features (e.g., flexible geometric structure, chromophoric character, luminescence, electrochemical behavior), Cu(I) complexes have attracted wide interest in several areas such as supramolecular chemistry,1 molecular machines,2 catalysis,3 ultrafast spectroscopy,4 solar energy conversion,5 optoelectronics6,7 and luminescence.8 In the latter area, the main goal is finding brightly emitting materials based on an abundant element as alternatives to standard triplet emitters, which typically contain expensive platinum group elements.9-12 Compared to the latter, Cu(I) systems may exhibit thermally activated delayed fluorescence (TADF).13 This means that the lowest lying triplet emitting level can get very close in energy (≈ 300– 1300 cm-1)8 to the upper lying singlet, which can be spontaneously populated at ambient temperature via reverse

intersystem crossing. Accordingly, emission comes from the singlet level (singlet harvesting) but its intrinsic lifetime is prolonged via the thermal equilibration with the longer-lived triplet. The overall result is that (i) both singlet and triplet excitons can be harvested and (ii) the excited state lifetime of the luminescent species can occur in the range 1-20 µs at room temperature.8 These features are particularly relevant for electroluminescent devices (e.g. OLEDs) because the efficiencies of electricity-to-light conversion are optimized and, on the other hand, saturation effects or undesired photochemical processes are significantly disfavored, due to the relatively short lifetime. The vast majority of luminescent Cu(I)-based complexes reported to date are cationic and the coordination environments explored have grown large. Compounds exhibiting good photoluminescence primarily include

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[Cu(NN)2]+ (where NN is a diimmine ligand such as 1,10phenanthroline,14 2,2’-bipyridine,15 or 4,5-diazafluorene16), [Cu(NN)(PP)]+ (where PP is a bis-phosphine ligand17,18), [Cu(PP)2]+,19,20 and other tetracoordinated systems.21 Recently, bright emission from tricoordinated22,23 and even biscoordinateded24 Cu(I) complexes often displaying Nheterocyclic carbene ligands has been reported. Some neutral Cu(I) compounds have been also prepared,25-28 including cyclometallated systems,29 but often their stability remains an issue. On the other hand, coordination polymers in which Cu(I) centers are connected to halogen ions (typically I–) in combination with heteroaromatic (N– or P–) ligands have been extensively investigated and may exhibit very strong emission.30,31 Other types of Cu(I)–based networks with intense luminescence have also been reported.32 Generally, Cu(I) complexes may suffer limited thermal and photochemical stability, particularly in solution. In many cases, the luminescence properties of Cu(I) compounds are only investigated in the solid state because solution instability compromises the reproducibility of experimental measurements. Complexation/decomplexation equilibria have been investigated in tetrahedral systems, which can be partially controlled by a thorough selection of ligands that can minimize steric congestion.33 Further instability can occur due to the strong reducing character of Cu(I) complexes in the excited state34 which, on the other hand can be fruitfully exploited in photoredox catalysis3 or photocatalytic water reduction.35 As part of this research, we became recently interested in heteroleptic copper(I) complexes constructed from macrocyclic phenanthroline ligands and bisphosphines.22,36,37 When compared to analogous [Cu(PP)(NN)]+ constructed from acyclic NN ligands, a higher stability has been evidenced for the systems incorporating macrocyclic phenanthrolines36 and steric constrains led to stabilization of unusual [Cu(PP)(NN)]+ derivatives.22 Whereas our first studies were mainly focused on their synthesis and on structural aspects, we now report a complete series of [Cu(PP)(NN)]+ incorporating macrocyclic phenanthroline ligands with different ring sizes along with detailed studies of their electronic properties. The copper(I) pseudorotaxanes are depicted in Chart 1. The behavior of the latter complexes is compared to that of the model complex [Cu(dmp)(POP)]BF4 (dmp = 2,9-dimethyl-1,10-phenanthroline; POP = bis[2(diphenylphosphino)phenyl] ether) previously reported.17,18,38 Comparative studies on OLED devices are also made.

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O

O

O

O +N

P

Cu

O

O

N

P

O O

O

BF4-

O

O

+

N

Cu

N

P O

BF4O

[Cu(m37)(POP)]BF4

P

+

Cu

N N

P

O

O

P

+

Cu

N N

P BF4-

O

P

O

O

O

O

O

[Cu(m30)(POP)]BF4

O

O

O

O

[Cu(m42)(POP)]BF4

BF4-

[Cu(dmp)(POP)]BF4

Chart 1. Pseudorotaxanes [Cu(mXX)(POP)]BF4 (mXX = m30, m37 or m42) and model compound [Cu(dmp)(POP)]BF4.

RESULTS AND DISCUSSION Synthesis. The copper(I) pseudorotaxanes were directly prepared from the corresponding macrocyclic ligands. The synthesis of compounds m3037 and m3736 was achieved according to a previously reported method. The preparation of macrocycle m42 is depicted in Scheme 1. Phenanthroline 136 was treated with tosylate 2 in the presence of CsF in CH3CN.39 Under these conditions, compound 1 was desilylated in situ to generate the corresponding bis-phenolate intermediate and subsequent reaction with 2 gave the desired alkylation product. Compound 3 was thus obtained in 63% yield. The macrocyclization was then performed under ring closing metathesis (RCM) reaction conditions40-49 using the first generation Grubbs’ catalyst. Importantly, the coordinating phenanthroline moiety does not interact with the ruthenium catalyst and macrocycle 4 was thus prepared in 50% isolated yield. Close inspection of the 1H NMR of 4 revealed that this compound was obtained as an E/Z isomeric mixture, one isomer being largely prevailing (ca. 90%). Finally, hydrogenation of the carbon-carbon double bond was carried out using Pd/C. Compound m42 was isolated in 57% yield. This moderate yield is due to the formation of secondary products resulting from a partial reduction of the phenanthroline moiety under these conditions. The purification of m42 was however easy and this compound was thus conveniently prepared on a gram scale.


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Journal of the American Chemical Society O OTBDMS

O

O

O

O

O O

N O

N

O 2

TsO

N

+N

P

Cu

O O

N

(a)

(a)

N

N

O

O

O

O

O

O

N

P

O O

O

BF4-

5 1

3

OTBDMS

O

O O

[Cu(5)(POP)]BF4

O

O

O

O (b) O

O

O O

O O

N

(b)

(c)

N

N

O

O

O

O

m42

O

Scheme 1. Preparation of m42. Reagents and conditions: (a) CsF, CH3CN, ∆ (63%); (b) first generation Grubbs’ catalysts, CH2Cl2, rt, (50%); (c) H2, Pd/C, THF (57%). The preparation of the Cu(I) complexed pseudorotaxane [Cu(m42)(POP)]BF4 was achieved by adding successively [Cu(CH3CN)4]BF4 (1 equiv.) and POP (1 equiv.) to a solution of m42 (1 equiv.) in CH2Cl2/CH3CN (Scheme 2). Compound [Cu(m42)(POP)]BF4 was then isolated in 82% yield by recrystallization (Et2O/CH2Cl2). Complexes [Cu(m30)(POP)]BF437 and [Cu(m37)(POP)]BF436 were prepared in a similar manner starting from m30 and m37, respectively.

1) Cu(CH3CN)4BF4 O

N

PPh2

2)

+

Cu

N N

P BF4-

O mXX

P

PPh2 POP

[Cu(mXX)(POP)]BF4 mXX = m30 (85%) mXX = m37 (75%) mXX = m42 (82%)

Scheme 2. Preparation of the Cu(I) pseudorotaxanes. In order to fully explore the possible synthetic pathways leading to pseudorotaxanes, we became also interested in performing the RCM reaction from a Cu(I)-complexed acyclic precursor. In this respect, the preparation of an acyclic derivative was attempted from ligand 537 (Scheme 3). A solution of POP (1 equiv.) and [Cu(CH3CN)4]BF4 (1 equiv.) in CH2Cl2/CH3CN was stirred for 0.5 h, then 5 (1 equiv.) was added. After 1 h, the solvents were evaporated. Compound [Cu(5)(POP)]BF4 was then isolated in 85% yield by crystallization in CH2Cl2/Et2O.

[Cu(m30)(POP)]BF4

N

O

BF4-

[Cu(6)(POP)]BF4

O

O

N

O

N

O

4

Cu P

O O

(c)

+N

P O

O

Scheme 3. Preparation of [Cu(m30)(POP)]BF4 from a Cu(I)-complexed acyclic precursor. Reagents and conditions: (a) POP, [Cu(CH3CN)4]BF4, CH2Cl2, CH3CN (85%); (b) second generation Grubbs’ catalyst, CH2Cl2 (36%); (c) H2, Pd/C, THF (40%). The first attempted cyclisation reactions of precursor [Cu(5)(POP)]BF4 were performed under RCM conditions using the Grubbs’ first generation catalyst in CH2Cl2. Under these conditions, no reaction was observed with 5 mol% of the ruthenium benzylidene catalyst. By using a larger amount of catalyst (30 mol%), the reaction started but consumption of the starting material stopped rapidly and no further reaction could be observed upon addition of new portions of catalyst to the reaction mixture. The desired Cu(I) complexed macrocyle was obtained at best in 5% yield under these conditions. The reaction conditions could be significantly improved by using the Grubbs’ second-generation catalyst. In this case, [Cu(5)(POP)]BF4 could be converted more efficiently into [Cu(6)(POP)]BF4. However, as in the previous case, consumption of the reagents stopped after a few hours of reaction and it was impossible to reach completion. Based on TLC and on the recovered starting material after column chromatography, ca. 20% of the reagent was not converted. Compound [Cu(6)(POP)]BF4 was isolated by column chromatography on SiO2 in 36% yield. This moderate yield is mainly due to difficulties encountered during the purification. Effectively, partial decomposition of the complex was observed on SiO2. Actually, part of the compound remained adsorbed on SiO2 all along the column (this was easily observed due to the yellow color of the compound) and could not be eluted anymore. Both the first and second generation Grubbs’ catalysts are generally tolerant to a wide range of functional groups,40 it is however known that none of them are suitable for olefin metathesis reactions involving free phosphine substrates.50-56 The presence of free phosphine ligands disfavors the equilibrium for olefin binding to the catalyst in the first step of a dissociative mechanism for the RCM.50-56 Indeed, competition between the better donating phosphine ligand and the olefin leads to inhibition of the catalyst.50-56 This effect is only partially prevented by the coordination of the phosphine ligand to the Cu(I) cation in the case of reagent [Cu(5)(POP)]BF4. Copper(I) complexes



being kinetically labile and thus allowing ligand exchange reactions in solution, the observed loss of activity for the RCM reaction may be explained by the slow release of small amounts of free phosphine in the reaction mixture. The improved yield obtained with the Grubbs’ second generation catalyst results from a kinetic effect, the RCM reaction being much faster with this catalyst than with the first generation one. Finally, Pd-catalyzed hydrogenation of the carbon-carbon double bond of [Cu(6)(POP)]BF4 gave [Cu(m30)(POP)]BF4 in 40% yield. As in the previous step, the moderate yield is mainly due to difficulties encountered during the purification.

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for the partially threaded one (A and its enantiomer A’).

Pseudorotaxanes [Cu(mXX)(POP)]BF4 (mXX = m30, m37 or m42) were characterized by NMR spectroscopy and electrospray mass spectrometry. These three complexes are perfectly stable when stored in the solid state. Dry samples were stored at room temperature under air for more than one year without any degradation. Compounds [Cu(mXX)(POP)]BF4 are also stable for several hours in CH2Cl2 solutions under argon. In the particular case of [Cu(m30)(POP)]BF4, oxidation of the POP ligand as well as the appearance of traces of Cu(II) species have been evidenced when the CH2Cl2 solutions are kept under air for several days. Similar observations were also done for CH2Cl2 solutions of the complexes incorporating larger macrocyclic ligands, however the oxidation is by far more limited for [Cu(m37)(POP)]BF4 and [Cu(m42)(POP)]BF4. These observations suggest a dynamic decoordination/coordination of the POP ligand. In this way, less stabilized Cu(I) species sensitive to oxygen are present in solution thus promoting the observed slow oxidations. The 1 H and 31P NMR spectra recorded for [Cu(mXX)(POP)]BF4 in CD2Cl2 at room temperature did however not reveal the presence of uncoordinated species. The dynamic exchange between coordinated and uncoordinated species is most probably faster than the NMR timescale and average spectra are obtained. By lowering the temperature, the dynamic exchange is slower and, at the same time, association is favored, thus the absence of signals corresponding to free ligands in the NMR spectra of [Cu(mXX)(POP)]BF4 recorded at low temperature does not constitute an evidence for a similar behavior at room temperature. Indeed, electrochemical studies revealed the presence of traces of [Cu(mXX)]+ species showing that a very minor amount of POP ligands is effectively noncoordinated in CH2Cl2 solution (vide infra). In the particular case of [Cu(m30)(POP)]BF4, peculiar molecular motions resulting from the folding of m30 were evidenced by variable temperature NMR studies and further supported by computational studies and an X-ray crystal structure.37 This prompted us to also investigate the behavior of [Cu(m37)(POP)]BF4 and [Cu(m42)(POP)]BF4. A similar dynamic exchange between different conformers was effectively evidenced for these two complexes. As shown in Figure 1, 31P NMR spectra of [Cu(m37)(POP)]BF4 and [Cu(m42)(POP)]BF4 recorded at low temperature revealed the appearance of a singlet attributed to the C2v symmetrical conformer (B) and a more complicated set of signals


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31

Figure 1. P NMR spectra (CD2Cl2, 202 MHz) of [Cu(m30)(POP)]BF4, [Cu(m37)(POP)]BF4 and [Cu(m42)(POP)]BF4 recorded at different temperatures. Insets: schematic representation of conformers A, B and A’ (top inset, A and A’ are enantiomers) and potential energy diagram of the dynamic exchange between A, B and A’.

In the latter case, the macrocyclic ligand of the complexes adopts a folded conformation in which one phenyl group of the POP ligand is located within the cavity of the macrocycle whereas the three others are located on one same side of the ring. As a result, the two P atoms of the POP ligand are no longer equivalent and two sets of signals are observed for this conformer in the 31P NMR spectra. The bridging unit of the POP ligand is actually quite large and generates steric congestion destabilizing conformer B. Despite increased ring sizes, the dynamic conformational equilibrium is still in favor of conformer A for both [Cu(m37)(POP)]BF4 and [Cu(m42)(POP)]BF4 as it was the case for the corresponding complex with the smallest macrocycle (m30). At higher temperatures, the dynamic exchange between conformers A and B is faster than the NMR timescale and a single resonance is observed in the 31P NMR spectra. The value of the free energy of activation (∆G‡) estimated from the NMR data57 for the dynamic exchange between conformers A and B is however decreased by increasing the size of the macrocyclic ligands (m30: 12 kcal/mol, m37: 9.3 kcal/mol and m42: 8.6 kcal/mol). Control experiments were also carried out with [Cu(dmp)(POP)]BF4. At low temperature, the 31P NMR spectrum of the dmp derivative shows a sharp singlet thus showing that the dynamic behavior observed for the pseudorotaxanes is specific to complexes incorporating a macrocyclic phenanthroline ligand (Figure S4). Electrochemical properties. The electrochemical properties of [Cu(mXX)(POP)]BF4 (mXX = m30, m37 or m42) were determined by cyclic voltammetry (CV) and

Osteryoung Square Wave Voltammetry (OSWV). All the experiments were performed at room temperature in CH2Cl2 solutions containing tetra n-butylammonium tetrafluoroborate (0.10 M) as supporting electrolyte and ferrocene (Fc) as internal reference, with a Pt wire as the working electrode and a saturated calomel electrode (SCE) as a reference. Potential data for all of the compounds are collected in Table 1 and the voltammograms are shown in Figures 2 and S15-S20. For comparison purposes, the redox potentials of model compound [Cu(dmp)(POP)]BF4 obtained under identical experimental conditions are also included in Table 1.58 Table 1. Electrochemical data of [Cu(mXX)(POP)]BF4 (mXX = m30, m37 or m42) determined by OSWV on a Pt working electrode in CH2Cl2 + 0.1 M n-Bu4NBF4 at room temperature.a,b Ferrocene has been used as internal reference. EOx1 [Cu(m30)(POP)]BF4

EOx2

+1.35

c

+1.72

−1.65

d

+1.73

−1.63

+1.50

[Cu(m42)(POP)]BF4

+1.52

[Cu(dmp)(POP)]BF4 a

−1.66

d

[Cu(m37)(POP)]BF4

e

ERed

+1.45

d

-1.66

OSWVs were obtained using a sweep width of 20 mV, a b frequency of 20 Hz, and a step potential of 5 mV; Potential values in Volt vs. SCE (Fc+/Fc is observed at 0.55 V ± 0.01 V c d vs. SCE); Chemically irreversible process in CV Electro-


Journal of the American Chemical Society chemically irreversible process in CV as the oxidation of the metal center is immediately followed by the oxidation of the e phosphorus ligand. From Ref. 58.

Photophysical properties. Experimental measurements were made on freshly prepared samples bubbled with argon for at least 20 minutes. All the pseudorotaxanes exhibit good stability at room temperature upon deaeration and under normal daily light for some hours in CH2Cl2, as shown by the absorption spectra recorded over time (Figures S21–S23). The UV-VIS absorption spectra of [Cu(mXX)(POP)]BF4 (XX = 30, 37, 42) in CH2Cl2 are gathered in Figure 3, excitation spectra are reported in Figures S24–S26. They are similar to previously reported spectra of heteroleptic cuprous complexes with phenanthroline and POP ligands, including [Cu(dmp)(POP)]BF4.17,18,38,62-65 In particular, they show a relatively strong band in the UV around 280 nm,66 mainly attributable to the phenanthroline ligand with some contribution from the POP moiety.67 Additionally, a broader and weaker band at about 380 nm is observed, due to metal-to-ligand-charge-transfer (MLCT) transitions from the copper center to the phenanthroline ligand.17,18,38,62-65 The spectra of the complexes with the largest macrocycles (m37, m42) are nearly superimposable, whereas the smaller analogue exhibits slightly broader features, suggesting a more distorted coordination environment. 10

[Cu(m30)(POP)]BF4 [Cu(m37)(POP)]BF4 [Cu(m42)(POP)]BF4 [Cu(dmp)(POP)]BF4

3000

8 2000

−1

In the cathodic region, all the pseudorotaxanes [Cu(mXX)(POP)]BF4 revealed the typical electrochemical response of [Cu(NN)(PP)]+ derivatives58 and the observed one-electron transfer process is centered on the phenanthroline moiety. In the anodic region, the one-electron transfer attributed to the Cu(II)/Cu(I) redox couple is observed at +1.35 V vs. SCE for pseudorotaxane [Cu(m30)(POP)]BF4. It can be noted that this oxidation is preceded by a wave of small intensity at +1.02 V vs. SCE (Figure 2). The latter was tentatively ascribed to the presence of small amounts of [Cu(m30)]+ in solution as already mentioned (vide supra). Moreover, cyclic voltammetry revealed an electrochemical instability for [Cu(m30)(POP)]BF4 and decomposition was evidenced upon oxidation. In contrast, the behavior of [Cu(m37)(POP)]BF4 and [Cu(m42)(POP)]BF4 is closer to the one of the model compound [Cu(dmp)(POP)]BF4. It can be noted that the oxidation of the Cu(I) center is slightly more difficult in the case of [Cu(m37)(POP)]BF4 and [Cu(m42)(POP)]BF4 when compared to [Cu(dmp)(POP)]BF4 (∆E = 50 and 70 mV, respectively). Indeed, the increased size of the 2,9-substituents on the phenanthroline ligand in [Cu(m37)(POP)]BF4 and [Cu(m42)(POP)]BF4 prevents the formation of a more flattened structure appropriate for the Cu(II) oxidation states.34,59-61 The potential shift results therefore from the destabilization of the Cu(II) complexes as typically observed in the case of homoleptic [Cu(NN)2]+ complexes.

fect is progressively suppressed. This is also consistent with the differences observed along the series for the free enthalpy of activation (∆G‡) estimated from the NMR data for the dynamic exchange between conformers.

6

1000

4

−1

ε / 10 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

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0

4

350

400

450

500

2

0 250

300

350 400 450 Wavelength / nm

500

550

Figure 3. Absorption spectra in CH2Cl2 at 298 K.

Figure 2. OSWVs (anodic scans) on a Pt electrode in CH2Cl2 + 0.1 M [nBu4N][BF4] at room temperature (frequency 20 Hz, amplitude 20 mV, step potential 5 mV).

For both [Cu(m37)(POP)]BF4 and [Cu(m42)(POP)]BF4, the metal-centered oxidation is preceded by a wave of very small intensity as observed for the pseudorotaxane incorporating m30. The intensity of this wave is however significantly smaller for [Cu(m37)(POP)]BF4 and virtually absent in the case of [Cu(m42)(POP)]BF4. Indeed, the steric congestion resulting from the macrocyclic nature of the NN ligand is high for the Cu(I) pseudorotaxane with the smallest macrocycle (m30) thus generating some instability. By increasing the size of the macrocycle, this ef-

The photoluminescence properties of the three pseudorotaxanes were investigated both at 298 K (CH2Cl2 solution, PMMA matrix, powder samples, neat films) and at 77 K (CH2Cl2). Luminescence spectra in CH2Cl2 at 298 K are nearly identical in shape and width and show extensive overlap also with [Cu(dmp)(POP)]BF4; only a small blue-shift (8 nm) is found for the compound with the smallest ring (Figure 4, Table 2).


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Emission 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


400

450

500


700

750

800

Figure 4. Luminescence spectra in CH2Cl2 at 298 K (full line) and 77 K rigid matrix (dotted line).

Similarly to heteroleptic [Cu(NN)(PP)]+ complexes previously reported17,18,38,62-65 the photoluminescence quantum yield (PLQY, Table 2) is weak in aerated solution (Φem ≈ 0.7–0.8 %), but gets remarkably enhanced upon oxygen removal (Φem ≈ 20 – 30 %). Table 2. Photophysical data in CH2Cl2 at 298 and 77 K. Double entries for each complex refer to oxygen free (top) and airequilibrated samples (bottom). b

CH2Cl2 at 298 K λem (nm) [Cu(m30)(POP)]BF4

560

[Cu(m37)(POP)]BF4

568

[Cu(m42)(POP)]BF4

568

[Cu(dmp)(POP)]BF4

565

CH2Cl2 at 77 K 4 −1

4 −1

Φem (%) a

τ (µs)

kr (10 s )

knr (10 s )

28.4

10.9

2.61

6.56

0.84

0.26

3.23

381

19.7

9.0

2.26

8.86

0.68

0.26

2.62

382

22.9

10.0

2.30

7.70

0.73

0.22

3.32

451

22.6

11.5

2.09

6.65

a

λem (nm)

τ (µs)

546

321

525

173

525

178

518

211

c

76 b

Measured with respect to quinine sulfate (1N, H2SO4) as standard (Φem = 0.546). Under these conditions a weak emission band on the high energy side has been detected and is attributed to phosphorescence from some free phenanthroline ligand c (Figure S28), by means of lifetime mapping and time gated luminescence measurements. This value is substantially longer with respect to what reported in ref. 58 (25 µs), when our instrumental apparatus could not explore time windows above a few tens of µs.

In parallel, excited state lifetimes are increased from 0.2 – 0.3 µs to 9 – 11 µs (Table 2). This trend supports a triplet character (3MLCT) of the observed excited state.17,18,38,62-65 In rigid CH2Cl2 at 77 K, the emission spectra are blueshifted with respect to 298 K. The shift is less pronounced in the smallest system, again suggesting a more constrained environment, taking also into account that [Cu(dmp)(POP)]BF4 shows the most pronounced blueshift.

lowest singlet and triplet states are thermally equilibrated)68 but when the matrix is solid, the temperature decrease (178–77 K) leads to a blue shift, because rigidochromic effects in the glass matrix prevail over electronic ones (Figure S27).

By recording the emission spectra of the three pseudorotaxanes in a wide temperature range in CH2Cl2 (77– 308 K), we observed that the spectral shift is not homogeneous. In the liquid CH2Cl2 domain, the temperature decrease (308–178 K) brings about a red shift (in line with the typical behaviour of Cu(I) complexes in which the



Page 8 of 31

Figure 5. Luminescence spectra in PMMA 1% wt (full lines) and as powder samples at 298 K (dashed lines).

The luminescence properties were further investigated in PMMA rigid matrix (1% wt) and as powders at 298 K; the spectra are reported in Figure 5 and the related photophysical data in Table 3. Emission measurements were also made in neat films and are reported in the Supplementary Information (Figure S29 and Table S1). The spectra are blue-shifted compared to room temperature solution due to rigidochromic effects and photoluminescence quantum yields are substantially higher particularly in PMMA, where they are all above 50%. Emission decays in PMMA are best fitted with biexponential functions yielding lifetimes in the range 20-80 µs. i.e., higher than in deaerated CH2Cl2 solution, but one order of magnitude shorter than at 77 K. The rather different excited state lifetimes in various media at different temperatures prompted us to investigate the emission behavior of the three pseudorotaxanes and of the reference compound in solid as a function of temperature. Emission spectra of the three pseudorotaxanes and of the reference compound [Cu(dmp)(POP)]BF4 as powders in the range 78-338 K are gathered in Figure 6 and S30-31 (integrals of luminescence spectra in Figures S32–S35). The ubiquitous red-shift as a function of temperature suggests the occurrence of TADF in solid samples. This hypothesis is corroborated by a marked elongation of the excited state lifetime in passing from room temperature (≈ 15 µs) to 77 K (> 100 µs), which is indicative of tripletto-singlet excited state thermal equilibrium.8 Interestingly, spectral red-shift at low temperatures is less pronounced in the pseudorotaxane systems, possibly as a function of a different, more constrained coordination environment, which impacts the singlet-triplet energy gap. Such gap has been evaluated by recording temperature dependent emission spectra and excited state lifetimes.

PMMA (1% wt)

[Cu(m30)(POP)]BF4

powders

λem (nm)

Φem (%)

τ1 (µs)

τ2 (µs)

λem (nm)

Φem (%)

τ (µs)

532

57

18.0

36.5

553

41

16.3


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Journal of the American Chemical Society a

[Cu(m37)(POP)]BF4

520

51

22.8

57.9

548

15

14.9

[Cu(m42)(POP)]BF4

520

53

24.0

63.0

538

32

17.1

[Cu(dmp)(POP)]BF4

520

65

25.3

75.1

527

37

27.5

Table 3. Photophysical data of the complexes in PMMA 1% wt and as powder at 298 K. a

This compound exhibits a biexponential decay with a short component of 7.29 µs

whereas the pseudorotaxane with the largest ring has a remarkably longer singlet lifetime. This confirms that the singlet and triplet parameters are extremely sensitive to relatively small structural differences.

Figure 7. Excited state lifetimes in the temperature range 78338 K (powder samples).

Table 4. Energy splitting ΔE(S1−T1) between the first excited singlet and triplet states (S1, T1) and related excited state lifetimes, calculated according to Eq. (1).

Figure 6. Luminescence spectra of [Cu(dmp)(POP)]BF4 (top) and [Cu(m42)(POP)]BF4 (bottom) as powders in the temperature range 78-338 K. The top horizontal scale is in nm.

The excited state lifetimes as a function of temperature are fitted using equation (1): (1) where τexp is the measured excited state lifetime (see Experimental section for details), ΔE(S1−T1) is the energy separation between the lowest excited singlet and triplet states of the copper complexes, τ(S1) and τ(T1) are the related excited state lifetimes and kB is the Boltzmann constant. The parameters fitting the plots of Figure 7 are reported in Table 4 and show two interesting trends: (i) the energy gap of the pseudorotaxanes is constantly smaller than that of the reference compound; (ii) the pseudorotaxane with the smallest macrocycle has a remarkably longer triplet lifetime compared to all the other compounds,

τ(S1)

ΔE(S1−T1) (eV)

ΔE(S1−T1) -1 (cm )

(ns)

τ(T1) (µs)

[Cu(m30)(POP)]BF4

0.121

970

55

261

[Cu(m37)(POP)]BF4

0.109

880

66

122

[Cu(m42)(POP)]BF4

0.111

900

100

167

[Cu(dmp)(POP)]BF4

0.134

1080

58

169

The values of ΔE(S1−T1) are relatively high when compared to series of Cu(I) complexes with different ligands,8 but in line with compounds displaying phenanthroline and/or POP chelators.8,68 It has to be stressed again that a TADF behavior all across the examined temperature range is observed only in the powder samples and not in CH2Cl2 (see above). This observation seems to be more general, as other investigators have often determined the singlet-triplet energy gap and the TADF behavior of luminescent Cu(I) complexes only as powder solid samples.8,27,69 OLED testing. [Cu(m42)(POP)]BF4 has been selected for the preparation of OLEDs owing to its electrochemical stability (see above) associated with an easy synthesis; its high PLQY in PMMA (Φem ≈ 53%) makes it also an excellent candidate for the purpose. [Cu(m42)(POP)]BF4 has


Journal of the American Chemical Society been incorporated as dopant in the emitting layer (EML) of an OLED device, affording intense green electroluminescence (EL) (Figure 8, inset). For comparison purposes, this device has been tested in parallel with an OLED exhibiting identical architecture but containing the reference complex [Cu(dmp)(POP)]BF4 as emitter, which lacks the macrocyclic phenanthroline ligand.

#+ Al LiF (0.5 nm) TPBi (25 nm) 85% BCPO : 15% Cu complex (50 nm) PEDOT:PSS (40 nm) ITO anode (120 nm)

EL Intensity / a.u.

!"#$$%$&'$()#(* GLASS SUBSTRATE [Cu(

)(POP)]BF4

[Cu(dmp)(POP)]BF 4

2.2 eV 2.4 eV 2.7 eV

400

450

500

550

600

650

700

750

800

Wavelength / nm

Figure 8 Electroluminescence spectra at 10 V of OLEDs. In the inset is reported a photograph of OLEDs based on [Cu(m42)(POP)]BF4.

Figure 9 shows the structure of the OLEDs and the energy levels of the materials studied. The devices were fabricated by a combination of wet and dry processes (spin coating and sublimation in high vacuum) onto a precleaned indium tin oxide (ITO) glass substrate (see Experimental Section). Holes were injected from the ITO anode and passed through a 40 nm thick transporting layer composed of PEDOT:PSS. Electrons were injected from an Al/LiF cathode and transported to the EML through a 25 nm thick layer of 2,2′,2"-(1,3,5-benzinetriyl)-tris(1phenyl-1-H-benzimidazole) (TPBi). Charges recombined in the 50 nm thick EML made of a bis-4-(Ncarbazolyl)phenyl)phenylphosphine oxide (BCPO) bipolar matrix,70,71 hosting the Cu complexes (15% wt) as Cubased emitters. EL spectra of the OLEDs are shown in Figure 8. Both OLED emission bands are located in the green region; the CIE coordinates of [Cu(m42)(POP)]BF4 and [Cu(dmp)(POP)]BF4 are (0.32, 0.53) and (0.33, 0.54), respectively. The EL spectra are similar and closely match the PL spectra of the complexes in rigid media. No significant contribution to the EL emission bands from the TBPi electron-transporting (hole-blocking) or BCPO binder layers is observed, indicating good charge carrier confinement within the EML and complete energy transfer from the excited states of BCPO (generated by charge carrier recombination) to the Cu complexes. Indeed, the OLEDs show excellent optoelectronic performance as shown in the data of Table 5.

PEDOT: PSS ITO 4.9 eV

BCPO : Cu complex

3.0 eV 350

Energy / eV

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 31

LiF/Al 2.9 eV

TPBi

5.1 eV 5.8 eV 5.8 eV

6.2 eV

Figure 9. OLED configuration (top) and energy level diagram (bottom). HOMO and LUMO levels of [Cu(m42)(POP)]BF4 were calculated by the redox potentials reported in Table 1.

Luminance of ≈ 1000 cd/m2 at about 10 V with Φ ≈ 9% and at about 11 V with Φ ≈ 7% were obtained for [Cu(m42)(POP)]BF4 and [Cu(dmp)(POP)]BF4, respectively. The luminance and external EL efficiency as function of driving voltage and current density of both OLEDs are displayed in Figure 10. The excellent OLED performance and parameters observed with [Cu(m42)(POP)]BF4 as emitter are also comparable – and even better – with respect to those previously reported for green OLEDs based on [Cu(dnbp)(DPEPhos)]+ (dnbp = 2,9-di-nbutylphenanthroline) by Adachi and coworkers.72


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Table 5. Optoelectronic performance of the OLEDs tested. Turn-on Voltage (V)

Elettroluminescence Efficiency

Maximum Luminance 2

2

Φmax (%)

Luminance (cd/m )

Lmax (cd/m )

Φ (%)

[Cu(m42)(POP)]BF4

4

10.5 (8.0 V)

100

12800 (14.0 V)

2.6

[Cu(dmp)(POP)]BF4

4

9.5 (7.5 V)

20

7740 (14.5 V)

2.1

presence of a phosphine ligand in the precursor, RCM has been an appropriate strategy to generate the corresponding pseudorotaxane. Steric congestions resulting from the macrocyclic nature of the phenanthroline ligand is at the origin of a dynamic conformational equilibrium in all the pseudorotaxanes, which has been evidenced with 31PNMR measurements over a wide temperature range. The macrocyclic component is indeed forced to adopt a folded conformation. When the macrocycle is small (m30), steric congestion is important and concomitant distortion of the coordination sphere around the copper(I) led to an electrochemical instability. By increasing the size of the macrocycle (m37 and m42), the steric congestion is reduced and does not affect the electrochemical behavior of the pseudorotaxanes. Photophysical studies in a variety of media and across extensive temperature ranges show that the pseudorotaxane structure sizably impacts the excited state properties of the complexes and, most importantly, enhances the stability of OLED devices. This finding may open a new route in the optimization of Cu(I) complexes for optoelectronics.

EXPERIMENTAL SECTION

Synthesis

Figure 10 Luminance versus applied voltage (top) and external EL efficiency versus driving current (bottom) of the OLEDs.

OLED performances were reproduced for five runs under argon atmosphere, excluding irreversible chemical and morphological changes in the OLEDs made of [Cu(m42)(POP)]BF4, whereas the luminance falls by about 20% for devices with [Cu(dmp)(POP)]BF4, indicating rapid degradation. The chemical stability under working condition is one of the big issues in the use of Cu complexes as active materials in OLEDs,25 and the enhanced device stability observed with [Cu(m42)(POP)]BF4 can be attributed to the presence of the pseudorotaxane structure that may prevent ligand detachment and chemical degradation.

CONCLUSION A series of copper(I) pseudorotaxanes has been efficiently prepared from POP and preconstructed macrocyclic phenanthroline derivatives with different ring sizes. Alternatively, these pseudorotaxanes have been also prepared by a clipping strategy from a Cu(I) complex incorporating an acyclic phenanthroline ligands. Despite the

General. Reagents were purchased as reagent grade and used without further purification. Compounds 1,37 2,73 5,37 m30,37 and m3736 were prepared according to previously reported procedures. Acetonitrile (CH3CN) and dichloromethane (CH2Cl2) were distilled over CaH2 under Ar. All reactions were performed in standard glassware under an inert Ar atmosphere. Evaporation and concentration were done at water aspirator pressure and drying in vacuo at 10-2 Torr. Column chromatography: silica gel 60 (230-400 mesh, 0.040-0.063 mm) was purchased from E. Merck. Thin Layer Chromatography (TLC) was performed on aluminum sheets coated with silica gel 60 F254 purchased from E. Merck. NMR spectra were recorded with a Bruker AC 300 or AC 400 spectrometer with solvent peaks as reference. Variable temperature NMR spectra were recorded with an Agilent DD2 500 MHz equipped with the OneNMR probe. MALDI-TOF mass spectra were carried out by the analytical service of the School of Chemistry (Strasbourg, France). Elemental analyses were performed by the analytical service of the Chemistry Department of the University of Strasbourg (France) or at the Laboratoire de Chimie de Coordination (Toulouse, France). Compound 3. A solution of 1 (1.20 g, 1.85 mmol) and 2 (1.40 g, 4.06 mmol) in CH3CN (100 mL) was added dropwise to a suspension of CsF (1.70 g, 11.13 mmol) in CH3CN (50 mL) heated at 80°C. After heating under reflux for 48



h, the resulting mixture was filtered through celite and concentrated. The residue was dissolved in CH2Cl2. The CH2Cl2 solution was washed with H2O, dried (MgSO4), filtered and evaporated. Column chromatography on SiO2 (CH2Cl2/cyclohexane 1/1 to CH2Cl2/CH3OH 0.7 %) gave 3 (0.88 g, 63 %) as a colourless glassy product. 1H NMR (CDCl3, 300 MHz): 8.14 (d, J = 8 Hz, 2H), 7.73 (s, 2 H), 7.46 (d, J = 8 Hz, 2H), 7.24 (d, J = 8.5 Hz, 4H), 6.86 (d, J = 8.5 Hz, 4H), 5.98-5.85 (m, 2H), 5.30-5.15 (m, 4H), 4.10-4.13 (m, 4H), 4.03-4.01 (m, 4H), 3.87-3.83 (m, 4H), 3.76-3.66 (m, 12H), 3.62 (m, 4H), 3.55-3.50 (m, 4H), 3.28-3.12 (m, 4H). MALDI-TOF MS: 765.3 ([M+H]+, calcd for C46H57N2O8: 765.41). Compound 4. Grubb’s 1st generation catalyst (5 mol%) was added to a 0.01M solution of 3 (0.88 g, 1.15 mmol) in CH2Cl2 at room temperature. Additional portions of catalyst (5 mol%) were added after 6, 20 and 30 h. After 48 h, the solution was concentrated and column chromatography on SiO2 (CH2Cl2/cyclohexane/toluene 50/50/1 to CH2Cl2/cyclohexane/toluene/CH3OH 50/50/1/1.5) gave 4 (0.42 g, 50 %) as a colourless glassy product. 1H NMR (CDCl3, 300 MHz): 8.14 (d, J = 8 Hz, 2H), 7.71 (s, 2 H), 7.52 (d, J = 8 Hz, 2H), 7.29 (d, J = 8.5 Hz, 4H), 6.85 (d, J = 8.5 Hz, 4H), 5.80-8.78 (m, 2 H), 4.11-4.08 (m, 4H), 4.02-4.00 (m, 4H), 3.83-3.80 (m, 4H), 3.72-3.64 (m, 12H), 3.59-3.56 (m, 4H), 3.52-3.46 (m, 4H), 3.31-3.26 (m, 4H). MALDITOF MS: 737.5 ([M+H]+, calcd for C44H53N2O8: 737.38). Compound m42. A mixture of 4 (0.4 g, 0.54 mmol) and Pd/C (10 wt % loading) in CH2Cl2 (20 mL) / EtOH (20 mL) was stirred at room temperature under positive H2 atmosphere. After 48 h, the mixture was filtered (Celite) and the solvents removed under reduced pressure. Column chromatography on SiO2 (CH2Cl2/cyclohexane/toluene 50/50/1 to CH2Cl2/toluene/CH3OH 99/1/0.75) gave m42 (0.23 g, 57 %) as a colourless glassy product. 1H NMR (CD2Cl2, 400 MHz): 8.20 (d, J = 8 Hz, 2H), 7.75 (s, 2 H), 7.57 (d, J = 8 Hz, 2H), 7.31 (m, 4H), 6.85 (m, 4H), 4.09-4.07 (m, 4H), 3.79-3.77 (m, 4H), 3.66-3.64 (m, 4H), 3.61-3.57 (m, 8H), 3.54-3.52 (m, 4H), 3.45-3.41 (m, 8H), 3.25-3.21 (m, 4H), 1.60 (m, 4H). 13C NMR (CD2Cl2, 100 MHz): 162.0, 157.5, 145.9, 136.6, 134.6, 129.9, 127.6, 126.0, 122.9, 114.8, 71.4, 71.2, 71.01, 70.99, 70.5, 70.0, 67.9, 41.6, 35.1, 26.8. MALDI-TOF MS: 739.3 ([M+H]+, calcd for C44H55N2O8: 739.39). General procedure for the preparation of [Cu(mXX)(POP)]BF4 from the macrocyclic ligands. A solution of the appropriate macrocyclic ligand (m30, m37 or m42, 1 equiv.) and Cu(CH3CN)4BF4 (1 equiv.) in a 7:3 CH2Cl2/CH3CN mixture was stirred under Ar for 0.5 h, then the POP ligand (1 equiv.) was added. After 1 h, the solvents were evaporated. The product was then purified as outlined in the following text. [Cu(m30)(POP)]BF4. Column chromatography (SiO2, CH2Cl2/1% MeOH) followed by recrystallization (slow diffusion of Et2O into a CH2Cl2 solution of the product) gave [Cu(m30)(POP)]BF4 (191 mg, 75% yield) as yellow crystals.

Page 12 of 31

1

H NMR (CD2Cl2, 300 MHz, 25°C): 8.43 (d, J = 7Hz, 2H), 7.98 (s, 2H), 7.68 (d, J = 7Hz, 2H), 7.31 (m, 6H), 7.15 (m, 8H), 7.05-6.82 (m, 14H), 3.15-3.07 (m, 20H), 2.92 (t, J = 6Hz, 4H), 2.67 (t, J = 6Hz, 4H), 1.32 (m, 8H). 13C {1H} NMR (CD2Cl2, 100 MHz, 25°C): 164.4, 157.4 (broad), 144.1, 138.3, 134.4 (broad), 134.3 (broad), 134.2, 132.7, 131.3 (broad), 131.9, 129.7 (t, 3JC,P = 4 Hz), 128.8, 127.0, 126.0 (broad), 125.4, 121.8 (broad), 71.6, 71.2, 71.0, 70.8, 70.7, 70.4, 38.9, 29.6, 27.2. 31P {1H} NMR (CD2Cl2, 162 MHz, 25°C): -13.57. ES-MS: 1127.39 ([M - BF4]+, calcd for C66H70N2O7P2Cu: 1127.40). Anal. Calcd. for C66H70N2O7P2CuBF4: C, 65.21; H, 5.80; N, 2.30. Found: C, 64.99; H, 6.01; N, 2.24. [Cu(m37)(POP)]BF4. Recrystallization by slow diffusion of Et2O into a CH2Cl2 solution of the crude product gave [Cu(m37)(POP)]BF4 (140 mg, 85%) as yellow crystals. 1 H NMR (CD2Cl2, 300 MHz): 8.43 (d, J = 7 Hz, 2H), 7.88 (s, 2H), 7.72 (d, J = 7 Hz, 2H), 7.21 (m, 6H), 7.08 (m, 4H), 7.00 (m, 8H), 6.83 (m, 8H), 6.65 (d, J = 7 Hz, 4H), 6.50 (d, J = 7 Hz, 2H), 6.18 (d, 4H), 4.17 (m, 4H), 3.85 (m, 4H), 3.70 (m, 4H), 3.62 (m, 4H), 3.51 (m, 8H), 3.12 (m, 4H), 2.73 (m, 4H). 13 C {1H} NMR (CD2Cl2, 100 MHz, 25°C): 162.0, 159.5 (t, 2JC,P = 5 Hz), 158.1, 143.8, 138.8, 134.2, 133.4 (t, 1JC,P = 17 Hz), 133.5 (t, 2JC,P = 8 Hz), 133.0, 132.8, 130.6, 129.6, 129.2 (t, 3JC,P = 4 Hz), 128.9, 126.8, 125.7 (m), 125.0 (t, 1JC,P = 16 Hz), 123.6, 121.4 (m), 115.1, 71.6, 71.4, 71.1, 71.0, 70.6, 68.5, 43.5, 32.7. 31P {1H} NMR (CD2Cl2, 162 MHz): -13.94. ES-MS: 1267.42 ([M BF4]+, calc. for C76H74N2O8P2Cu: 1267.422). Elemental analysis calcd for C76H74BCuF4N2O8P2.CH2Cl2: C 64.20, H 5.32, N 1.94; found: C 64.45, H 5.56, N 1.45. [Cu(m42)(POP)]BF4. Column chromatography (SiO2, CH2Cl2/1% MeOH) gave [Cu(m42)(POP)]BF4 (342 mg, 82% yield) as a yellow glassy product. 1H NMR (CD2Cl2, 300 MHz): 8.45 (d, J = 8.5 Hz, 2H), 7.87 (s, 2 H), 7.75 (d, J = 8.5 Hz, 2H), 7.18-7.09 (m, 8H), 7.05 (d, J = 8 Hz, 2H), 6.98-6.93 (m, 8H), 6.86-6.80 (m, 8H), 6.70 (d, J = 8.5 Hz, 4H), 6.47 (d, J = 8 Hz, 2H), 6.24 (d, J = 8.5 Hz, 4H), 4.174.14 (m, 4H), 3.87-3.84 (m, 4H), 3.73-3.70 (m, 4H), 3.663.63 (m, 4H), 3.60-3.57 (m, 4H), 3.52-3.49 (m, 4H), 3.403.36 (m, 4H), 3.16-3.11 (m, 4H), 2.75-2.71 (m, 4H), 1.58-1.54 (m, 4H). 13C {1H} NMR (CD2Cl2, 100 MHz, 25°C): 161.6, 159.4 (t, 2JC,P = 6 Hz), 157.7, 143.5, 138.5, 133.8, 133.2 (t, 1JC,P = 17 Hz), 133.0 (t, 2JC,P = 7 Hz), 132.6, 132.4, 130.2, 129.4, 128.8 (t, 3JC,P = 4 Hz), 128.6, 126.4, 125.2 (m), 124.7 (t, 1JC,P = 14 Hz), 123.2, 121.2 (m), 114.6, 71.4, 71.35, 71.05, 71.0, 70.5, 70.2, 68.1, 43.2, 33.5, 26.8. 31P {1H} NMR (CD2Cl2, 162 MHz): 13.59. ESI-TOF MS: 1339.5 ([M - BF4]+, calcd for C80H82CuN2O9P2: 1339.48). Elemental analysis calcd for C80H82BCuF4N2O9P2: C 67.30, H 5.79, N 1.96; found: C 67.32, H 5.77, N 1.85. [Cu(5)(POP)]BF4. A solution of POP (292 mg, 0.543 mmol) and Cu(CH3CN)4BF4 (171 mg, 0.543 mmol) in CH2Cl2 (50 mL) was stirred for 0.5 h, then 5 (300 mg, 0.543 mmol) was added. After 1 h, the solvents were evaporated. The residue was dissolved in a minimum of CH2Cl2 and the Cu(I) complex precipitated by addition of Et2O. Filtration yielded [Cu(5)(POP)]BF4 (575 mg, 85% yield) as an yellow-orange powder. 1H NMR (CD2Cl2, 400 MHz): 8.44

12 ACS Paragon Plus Environment

Page 13 of 31 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


(d, J = 8 Hz, 2H), 7.92 (s, 2H), 7.70 (d, J = 8 Hz, 2H), 7.336.99 (m, 28H), 5.91 (m, 2H), 5.30-5.14 (m, 4H), 3.99 (m, 4H), 3.56 (s, 8H), 3.48 (t, J = 4 Hz, 4H), 3.32 (t, J = 4 Hz, 4H), 2.93 (m, 4H), 2.77 (m, 4H), 1.46 (m, 4H). [Cu(6)(POP)]BF4. Grubb’s 2nd generation catalyst (5 mol %) was added to a 0.005 M solution of [Cu(5)(POP)]BF4 (575 mg, 0.463 mmol) in CH2Cl2. After 6 h at room temperature, an additional portion of catalyst (5 mol %) was added. After 6 h, the solvent was removed under vacuum. Column chromatography on SiO2 (CH2Cl2/1 to 4% MeOH) gave [Cu(6)(POP)]BF4 (200 mg, 36% yield) as a pale yellow solid. 1H NMR (CDCl3, 300 MHz): 8.48 (d, J = 8Hz, 2H), 8.01 (s, 2H), 7.68 (d, J = 8Hz, 2H), 7.29 (m, 6H), 7.14 (m, 8H), 7.05-6.78 (m, 14H), 5.49 (m, 2H), 3.67 (m, 4H), 3.21-3.10 (m, 14H), 2.90 (m, 4H), 2.68 (m, 4H), 1.32 (m, 6H). [Cu(m30)(POP)]BF4. A mixture of [Cu(6)(POP)]BF4 (200 mg, 0.164 mmol) and Pd/C (10 wt % loading, 20 mg) in CH2Cl2/EtOH (1:1) (30 mL) was stirred at room temperature under positive H2 atmosphere. After 4 h, the solution was concentrated and column chromatography on SiO2 gave [Cu(m30)(POP)]BF4 (80 mg, 40% yield) as a yellow powder.

Measurements and device fabrication Photophysics. Spectrofluorimetric grade dichloromethane was used as solvent for spectroscopic investigations. The absorption spectra were recorded with a Perkin-Elmer Lambda 950 spectrophotometer. For the photoluminescence experiments, the samples were placed in fluorimetric Suprasil quartz cuvettes (1 cm) and deaerated by bubbling argon for at least 20 minutes. The uncorrected emission spectra were obtained with an Edinburgh Instruments FLS920 spectrometer equipped with a Peltiercooled Hamamatsu R928 photomultiplier tube (PMT) (185−850 nm). An Edinburgh Xe 900 with 450 W xenon arc lamp was used as the excitation light source. The corrected spectra were obtained via a calibration curve supplied with the instrument. The luminescence quantum yields (ΦPL) in solution were obtained from the corrected spectra on a wavelength scale (nm) and measured according to the approach described by Demas and Crosby,74 using an air-equilibrated water solution of [Ru(bpy)3]Cl2 (ΦL = 0.028)75 and air-equilibrated water solution of quinine sulfate in 1 N H2SO4 (ΦL = 0.546)76 as references. The emission lifetimes (τ) in the microsecond time range were measured through the time-correlated single photon counting (TCSPC) technique using an HORIBA Jobin Yvon IBH FluoroHub controlling a spectrometer equipped with a pulsed SpectraLED (λexc = 370 nm; FWHM = 11 nm) as the excitation source and a redsensitive Hamamatsu R-3237-01 PMT (185–850 nm) as the detector. The analysis of the luminescence decay profiles was accomplished with the DAS6 Decay Analysis Software provided by the manufacturer, and the quality of the fit

was assessed with the χ2 value close to unity and with the residuals randomly distributed along the time axis. To record the 77 K luminescence spectra, samples were put in quartz tubes (2 mm inner diameter) and inserted into a special quartz Dewar flask filled with liquid nitrogen. Solid samples were prepared following three different procedures: (i) poly(methyl methacrylate) (PMMA) films containing 1 wt % of the complex drop-cast from dichloromethane solutions; (ii) neat films drop-cast from dichloromethane solutions; (iii) powders, as obtained after the crystallization, grinded and placed in quartz tubes (2 mm inner diameter) or in between two quartz slides. The thickness of the films was not determined. Solid-state ΦPL values were calculated by corrected emission spectra obtained from an Edinburgh FLS920 spectrometer equipped with a barium sulfate-coated integrating sphere (diameter of 3 in.) following the procedure described by Würth et al..77 For temperature-dependent measurements, the samples (powders or CH2Cl2 solution) were placed inside an Oxford Optistat DN variable-temperature liquid-nitrogen cryostat (operating range: 77–500 K) equipped with an ITC5035 temperature controller and interfaced with the aforementioned Edinburgh FLS920 spectrometer. The temperature-dependent emission lifetimes were measured through the Multi-Channel Scaling Single Photon Counting (MCS-SPC) technique with the use of the same luminescence spectrometer described above and equipped with a 60W xenon flashlamp (Edimburgh µF920H) as the excitation source (100 Hz; 2 µs pulse width) and the aforementioned PMT as detector (minimum response 600 ps). The analysis of the luminescence decay profiles upon deconvolution of the Instrumental Response Function (IRF) was accomplished with the software provided by the manufacturer, and the quality of the fit was assessed following above mentioned conditions. The decays were fitted as biexponential: the shorter lifetime contributes below 20% and is attributed to scattering, whereas the longer lifetime is taken as the experimental value. Experimental uncertainties are estimated to be ±8% for τ determinations, ±20% for ΦPL, and ±2 nm and ±5 nm for absorption and emission peaks, respectively. OLED fabrication and assessment. OLEDs were fabricated on glass substrates pre-coated with a 120 nm-thick layer of indium tin oxide (ITO) with a sheet resistance of 20 Ω per square. The substrates were cleaned by ultrasonication in acetone and 2-propanol baths and then placed in a UV-cleaner for 25 min. After the treatment of the substrates, a 40 nm-thick layer of poly(3,4ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS, Clevios P VP AI 4083) was spin-coated (4000 rpm) and then the substrates were placed in an oven at 140 °C for 10 min. After the ITO/PEDOT:PSS substrates were cooled down, a 50 nm-thick film of emitting layer composed of 15 wt% of Cu complex and 85 wt% of bis-4-(N-carbazolyl)phenyl)phenylphosphine oxide)



(BCPO, Lumtec) host was spin-coated (2000 rpm) in clean room environment from a 8 mg/mL dichloromethane solution, which had the above indicated weight % concentrations of Cu complex and BCPO. The layers of the OLED devices were deposited in clean room environment by thermal evaporation under high vacuum of ~ 10–6 hPa without vacuum interruption. First, a 25 nm thick electron transporting layer of 2,2’,2"-(1,3,5-benzinetriyl)tris(1-phenyl-1-H-benzimidazole) (TPBi, Jilin OLED Material Tech Co., Ltd) was evaporated and then the cathode layer consisting of 0.5 nm-thick LiF (Sigma Aldrich, ≥ 99.98%) and 100 nm-thick Al cap. All solvents employed in substrates cleaning and device preparation were purchased from Sigma Aldrich and were of analytical grade. The current-voltage characteristics were measured with a Keithley Source-Measure unit, model 236, under continuous operation mode, while the light output power was measured with an EG&G power meter, and electroluminescence spectra recorded with a StellarNet spectroradiometer. All measurements were carried out at room temperature under argon atmosphere. The OLED devices had a lighting area of 7.1 mm2.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. NMR spectra, OSWVs and cyclic voltammograms, absorption emission and excitation spectra, integration of the emission spectra. Figures S1-S35. Table S1.

AUTHOR INFORMATION Corresponding Author * [email protected] * [email protected] * [email protected] * [email protected]

ACKNOWLEDGMENT Financial support by the CNR (PHEEL; Progetto Bandiera NCHEM), the CNRS (PICS n° 6840), the University of Strasbourg, the International Center for Frontier Research in Chemistry and the LabEx “Chimie des Systèmes Complexes” is gratefully acknowledged. We further thank M. Schmitt for high-field NMR measurements, J.-M. Strub for the mass spectra and A. Sournia-Saquet (LCC) for electrochemical measurements.

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SYNOPSIS TOC


Page 17 of 31 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


Chart1 119x110mm (600 x 600 DPI)



Scheme1 124x105mm (600 x 600 DPI)


Page 18 of 31

Page 19 of 31 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


Scheme2 69x35mm (600 x 600 DPI)



Scheme3 101x77mm (600 x 600 DPI)


Page 20 of 31

Page 21 of 31 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


Figure1 354x265mm (72 x 72 DPI)



Figure2 310x209mm (72 x 72 DPI)


Page 22 of 31

Page 10 23 of 31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

3000

8

−1

2000

6

1000

4

−1

ε / 10 M cm


0

4

350

400

450

500

2

0 250

300



500

550



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

400

450

500



Page 24 of 31 [Cu(m30)(POP)]BF 4 [Cu(m37)(POP)]BF4 [Cu(m42)(POP)]BF4 [Cu(dmp)(POP)]BF4

700

750

800

Page 25 of 31


[Cu(m30)(POP)]BF4 [Cu(m37)(POP)]BF4 [Cu(m42)(POP)]BF4


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

[Cu(dmp)(POP)]BF4

400

450

500

ACS550 Paragon Plus Environment 600 650

Wavelength / nm

700

750

800

Wavelength / nm Journal of the American Chemical Society 450

600

700

800 78 K +?5> 98 K 118 K 138 K 158 K 178 K 198 K 218 K 238 K 258 K 278 K 298 K 318 K 338 K

Normalized Emission Spectra / 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

500

Page 26 of 31

2.8

2.6

2.4

2.2

2.0

1.8

1.6

Energy / eV Wavelength / nm 450

500

600

700

800

Normalized Emission Spectra / a.u.

78 K 98 K 118 K 138 K 158 K 178 K 198 K 218 K 238 K 258 K 278 K 298 K 318 K 338 K

2.8

2.6

ACS Environment 2.4Paragon Plus2.2

Energy / eV

2.0

1.8

1.6

Page 27 of 31

&'

!"#$%#

*+,-./!#0.1210345' *+,-./!60.1210345'

(")

Emission Lifetime / s

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


*+,-./'(0.1210345' *+,-.7/80.1210345'

("# %") %"# #") #"# %##

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Temperature / K


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EL 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

Page 28 of 31

[Cu(m42)(POP)]BF4 [Cu(dmp)(POP)]BF4

350

400

450

ACS Paragon Plus Environment 500 550 600 650

Wavelength / nm

700

750

800

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#+ Al LiF (0.5 nm) TPBi (25 nm) 85% BCPO : 15% Cu complex (50 nm) PEDOT:PSS (40 nm) ITO anode (120 nm)

!"#$$%$&'$()#(* GLASS SUBSTRATE

2.4 eV

2.2 eV 2.7 eV

PEDOT: PSS ITO 4.9 eV

BCPO : Cu complex

3.0 eV Energy / eV

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


TPBi

5.1 eV 5.8 eV 5.8 eV ACS Paragon Plus Environment

6.2 eV

LiF/Al 2.9 eV

10

EL Efficiency / % ph/e

Luminance / cd/m

2

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

10 10 10 10 10 10 10


4

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3 2

1 0 -1

-2 -3

4

6

8 10 Applied Voltage / V

12

10

14


8 6 4 2 0 10

-6

-5

-4

10ACS Paragon Plus 10 Environment10

-3 2

Current Density / A/cm

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10

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Journal Page 31 ofof the 31American Chemical Society 1 2 3 4 5 6 7


Heteroleptic Copper(I) Pseudorotaxanes ... - ACS Publications

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