Tuning Emission of AIE-Active Organometallic Ir(III) Complexes by

Article pubs.acs.org/Organometallics

Tuning Emission of AIE-Active Organometallic Ir(III) Complexes by Simple Modulation of Strength of Donor/Acceptor on Ancillary Ligands Kai-Yue Zhao, Guo-Gang Shan,* Qiang Fu, and Zhong-Min Su* Institute of Functional Material Chemistry and National & Local United Engineering Lab for Power Battery, Faculty of Chemistry, Northeast Normal University, Changchun 130024, P. R. China S Supporting Information *

ABSTRACT: A new design strategy to tune emission color of aggregation-induced emission (AIE) Ir(III) complexes, by simply adjusting the strength of donor/acceptor on ancillary ligands, is reported. Herein, all studied Ir(III) complexes employ 1-(2,4difluorophenyl)-1H-pyrazole as cyclometalated ligands but different pyridine-1,2,4triazolyl moieties as ancillary ligands that were modified with carbazole end-capped alkyl groups, in which pyridine-1,2,4-triazolyl moieties and functionalized carbazole act as donor and acceptor units, respectively. The experimental and theoretical results clearly reveal the intrinsic relationship between structures and emission behaviors. Enhancing the ability of donor and/or acceptor leads to red-shifted emission and vice versa. In addition, one of the designed dyes exhibits the reversible and significant mechanochromic luminescent behavior thanks to its efficient AIE characteristic and structural modification, providing a feasible way to design multifunctional materials.

1. INTRODUCTION Phosphorescent Ir(III) complexes, as a kind of promising organic electronic material, have attracted increasing attention with respect to their potential applications in organic lightemitting devices (OLEDs), light-emitting electrochemical cells (LECs), and solar energy harvesters.1 Unlike conventional fluorescent counterparts, they possess the evident Stokes shifts, relatively long lifetime, good photo- and thermal stabilities, and the versatility in tuning emission color. Due to these intrinsic advantages, a variety of chemical sensors and bioimaging probes have been successfully constructed.2 To realize the highefficiency optoelectronic devices and sensors, the luminescent materials with efficient emissions, especially in the aggregation states, are highly desired. Similar to most luminophors, however, the strong phosphorescent emission of Ir(III) complexes is often weakened or even quenched in their aggregation states caused by the aggregation-caused quenching (ACQ) effect. The ACQ effect has significantly limited their practical applications as the phosphors are often required to be used in the aggregated states. Although various chemical and physical strategies have been adopted to alleviate the ACQ effect, such approaches always bring the complicated and expensive procedures for material and device preparations. In 2001, an intriguing aggregation-induced emission (AIE) phenomenon that is exactly opposite to ACQ has been observed by Tang’s group.3 Instead of emission quenching, AIE materials can emit strong light when aggregated into nanoparticles or in solid-state film. This finding paves a new avenue to construct highly efficient solid-state luminescent materials. It is thus proposed that AIE-active Ir(III) complexes would © XXXX American Chemical Society

possess more attractive optical characteristics, by combining the AIE and phosphorescent features together. However, up until now, the development of AIE Ir(III) materials is still in its infancy and only few examples have been reported, owing to the lack of clear molecular design principles.4 More recently, we and other groups have devoted tremendous efforts to the exploitation of AIE-active mononuclear and dinuclear Ir(III) complexes and demonstration of their potential application in sensors.5 Despite that these advances have been made, major challenges for design of such materials still remain. For example, how to turn the emission color of AIE Ir(III) complexes is a topic of continuing interest, as it is a key parameter for a given luminescent material. Recently, Zhu and his co-workers have develop a series of AIE-active Ir(III) complexes with tunable emissions by changing the type of cyclometalated ligands.4 However, the detailed structure− property relationship has not been well demonstrated. To establish a clear structure−emission color relationship, it would be ideal to investigate the intrinsic photophysical and electronic properties for structurally similar AIE Ir(III) complexes with tiny structural modification but significant color change. Keeping this in mind, herein, we designed and synthesized four structurally similar AIE Ir(III) complexes (B1, G1, Y1, and O1) to easily understand the emission color changes caused by their structural differences (see Scheme 1). From the structural point of view, the ancillary ligand generally comprises the triazole−pyridine unit and carbazole-based functional moiety as Received: October 13, 2016

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DOI: 10.1021/acs.organomet.6b00788 Organometallics XXXX, XXX, XXX−XXX

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performed under a nitrogen atmosphere through using standard Schlenk techniques. 1H NMR spectra were recorded on a Bruker Avance 500 MHz spectrometer with tetramethylsilane as internal standard. UV−vis absorption spectra were recorded on a Cary 500 spectrometer. Photoluminescence spectra of all complexes were obtained through the F-4600 FL spectrophotometer. The excitedstate lifetimes (τ) and photoluminescence quantum yields (Φp) in solution from the samples were recorded on a spectrofluorimeter (Edinburgh FLS-920). 2.2. Synthesis. Synthesis of the Iridium(III) Complexes Used in This Work. The experimental details and characterization data for the used ligands are listed in the Scheme S1 in the Supporting Information. Synthesis of Dimeric Complex [(dfppz)2Ir(μ-Cl)2Ir(dfppz)2]. [(dfppz)2Ir(μ-Cl)2Ir(dfppz)2] was synthesized according to our previously reported procedure.5e Hdfppz (1.80 g, 10.00 mmol) and IrCl3·3H2O (1.40 g, 4.00 mmol) were dissolved in a mixture of 2ethoxyethanol/water (60 mL, 3:1 V/V) solution. The reaction mixture was degassed repeatedly and refluxed for 20 h while protected from light and oxygen. The reaction was cooled down to room temperature, and 5 mL of water was added. The resultant solid was filtered and washed with 25 mL of water, 25 mL of ethanol, and 25 mL of diethyl ether (Et2O), then dried in vacuo. The crude dichloro-bridged diiridium complex was used without any further purification. Synthesis of Complex B1. Scheme 2 exhibits the synthetic routes of the iridium(III) complexes B1, G1, Y1, O1, and G2. The general procedure for the synthesis of them is described as follows: a suspension of μ-dichloro bridged iridium-dimer (1.0 equiv) and the desired ancillary ligand (2.2 equiv) in 1,2-ethanediol was degassed by multiple vacuum and Ar2 purging cycles and stirred at 150 °C for 12 h, protected from light. The reaction mixture was cooled down to room temperature and diluted with water subsequently. To ensure no chloride counterion in the system, an excess of NH4PF6 (2 g in 200 mL of water) was added to afford the desired precipitate.1f The resultant solid was filtered and further purified via silica gel column chromatography and recrystallized from dichloromethane and petroleum ether. Following the general procedure, B1 is obtained as white solids (65%). 1H NMR (500 MHz, d6-DMSO): δ = 8.64 (d, J = 8 Hz, 1H), 8.60 (d, J = 3 Hz, 1H), 8.51 (d, J = 8 Hz, 1H), 8.24−8.28 (m, 1H), 8.16 (d, J = 8 Hz, 2H), 8.02 (d, J = 4.5 Hz, 1H), 7.69−7.72 (m, 1H),

Scheme 1. Chemical Structures of Ir(III) Complexes B1, G1, Y1, O1, and G2

acceptor and donor, respectively. The study clearly shows that the emission colors can be systematically tuned from blue-green to orange-yellow by simply modifying the ability of donor and acceptor on ancillary ligands. As the strength of donor and/or acceptor is increased, the different degrees of bathochromic shift in emission are observed. To further check the obtained result, another AIE Ir(III) complex, G2, has been prepared, whose emission behavior matches well the above trend. For the first time, we present a feasible and simple way to control the emission color of AIE Ir(III) complexes. In addition, benefiting from the appealing AIE feature of G1 that prevents effectively quenching in the solid-state, the reversible efficient mechanochromic luminescent behavior is also realized.

2. EXPERIMENTAL SECTION 2.1. General Information. Commercial reagents were used as received unless specially stated. The solvents for syntheses were freshly distilled over appropriate dying reagents. All experiments were

Scheme 2. Synthetic Routes of the Iridium(III) Complexes

B

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Organometallics 7.59−7.62 (m, 3H), 7.42−7.45 (m, 2H), 7.04−7.21 (m, 5H), 6.79 (t, J = 2.5 Hz, 1H), 6.73 (t, J = 2.5 Hz, 1H), 5.58 (d, J = 8 Hz, 2H), 4.69− 4.80 (m, 2H), 4.42−4.47 (m, 2H), 2.01−2.02 (m, 2H), 1.89−1.90 (m, 2H), 1.67 ppm (s, 3H). 19F NMR (470 MHz, d6-DMSO): −67.33 (d, J = 711.11 Hz, 6F), −109.62 to −109.67 (m, 1F), −110.14 to −110.08 (m, 1F), −119.87 to −119.91 (m, 1F), −120.06 to −120.10 ppm (m,1F). MS Calcd: m/z 932.2 for [M − PF6] (C42H33F4IrN9), found: m/z 932.2. Anal. Calcd for C42H33F10IrN9P: C, 46.84; H, 3.09; N, 11.71. Found: C, 46.91; H, 3.15; N, 11.63. Synthesis of Complex G1. G1 was prepared according to the general procedure described above (Yield: 72%). 1H NMR (500 MHz, d6-DMSO): δ = 8.65−8.67 (m, 2H), 8.63 (d, J = 2.5 Hz, 1H), 8.32− 8.35 (m, 1H), 8.16 (d, J = 7.5 Hz, 2H), 8.04 (d, J = 5.5 Hz, 1H), 7.77− 7.79 (m, 2H), 7.65 (d, J = 8.5 Hz, 2H), 7.43−7.46 (m, 2H), 7.15−7.24 (m, 4H), 7.01−7.15 (m, 1H), 6.83 (t, J = 3.0 Hz, 1H), 6.76 (t, J = 2.5 Hz, 1H), 5.48−5.50 (m, 1H), 5.39−5.41 (m, 1H), 4.84−4.93 (m, 2H), 4.51 (t, J = 7.5 Hz, 2H), 2.13 (d, J = 6.0 Hz, 2H), 1.97−2.01 ppm (m, 2H). 19F NMR (470 MHz, d6-DMSO): δ = −61.30 (s, 3F), −67.33 (d, J = 711.11 Hz, 6F), −109.30 to −109.27 (m, 1F), −111.06 to −111.03 (m, 1F), −119.68 to −119.66 (m, 1F), −121.56 to −121.54 ppm (m,1F). MS Calcd: m/z 986.2 for [M − PF6] (C42H30F7IrN9), found: m/z 986.2. Anal. Calcd for C42H30F13IrN9P: C, 44.61; H, 2.67; N, 11.15. Found: C, 44.54; H, 2.60; N, 11.04. Synthesis of Complex Y1. Y1 was prepared according to the general procedure described above (Yield: 74%). 1H NMR (500 MHz, d6-DMSO): δ = 8.65 (d, J = 2.5 Hz, 1H), 8.61 (d, J = 3.0 Hz, 1H), 8.50 (d, J = 8.0 Hz, 1H), 8.25−8.28 (m, 1H), 8.01 (d, J = 5.5 Hz, 1H), 7.87 (s, 2H), 7.69−7.72 (m, 1H), 7.58 (d, J = 2.5 Hz, 1H), 7.43 (d, J = 8.5 Hz, 2H), 7.16−7.22 (m, 3H), 7.05−7.15 (m, 2H), 6.79 (t, J = 3.0 Hz, 1H), 6.72 (t, J = 2.5 Hz, 1H), 5.56−5.58 (m, 2H), 4.66−4.78 (m, 2H), 4.34−4.39 (m, 2H), 2.45−2.50 (m, 6H), 1.95−1.99 (m, 2H), 1.81− 1.86 (m, 2H), 1.65 ppm (s, 3H). 19F NMR (470 MHz, d6-DMSO): δ = −67.33 (d, J = 711.11 Hz, 6F), −109.65 to −109.62 (m, 1F), −111.16 to −111.14 (m, 1F), −119.92 to −119.89 (m, 1F), −121.10 to −121.93 ppm (m,1F). MS Calcd: m/z 960.2 for [M − PF6] (C44H37F4IrN9), found: m/z 960.2. Anal. Calcd for C44H37F10IrN9P: C, 47.83; H, 3.38; N, 11.41. Found: C, 47.92; H, 3.30; N, 11.34. Synthesis of Complex O1. O1 was prepared according to the general procedure described above (Yield: 76%). 1H NMR (500 MHz, d6-DMSO, ppm): δ = 8.32 (d, J = 3.0 Hz, 1H), 8.30 (d, J = 3.0 Hz, 1H), 8.20 (d, J = 8.5 Hz, 1H), 8.06 (t, J = 8.0 Hz, 1H), 7.95 (d, J = 5.5 Hz, 1H), 7.80 (s, 2H), 7.41−7.43 (m, 1H), 7.30 (d, J = 8.0 Hz, 2H), 7.23−7.26 (m, 2H), 7.16 (d, J = 2.5 Hz, 1H), 6.57 (d, J = 2.0 Hz, 1H), 6.67−6.71 (m, 1H), 6.58−6.61 (m, 1H), 6.55−6.57 (m, 1H), 6.50 (t, J = 2.5 Hz, 1H), 5.53−5.55 (m, 1H), 5.46−5.48 (m, 1H), 4.77 (t, J = 7.0 Hz, 2H), 4.37 (t, J = 6.5 Hz, 2H), 2.50 (s, 6H), 2.05−2.17 ppm (m, 4H). 19F NMR (470 MHz, d6-DMSO): δ = −61.29 (s, 3F), −67.33 (d, J = 711.11 Hz, 6F), −109.30 to −109.27 (m, 1F), −111.06 to −111.03 (m, 1F), −119.69 to −119.67 (m, 1F), −121.58 to −121.56 ppm (m,1F). MS Calcd: m/z 1014.2 for [M − PF6] (C44H34F7IrN9), found: m/z 1014.2. Anal. Calcd for C44H34F13IrN9P: C, 45.60; H, 2.96; N, 10.88. Found: C, 45.68; H, 3.03; N, 10.79. Synthesis of Complex G2. G2 was prepared according to the general procedure described above (Yield: 68%). 1H NMR (500 MHz, d6-DMSO): δ = 8.68 (d, J = 8.0 Hz, 1H), 8.61−8.65 (m, 2H), 8.36 (t, J = 8.0 Hz, 1H), 8.13−8.16 (m, 3H), 7.80−7.83 (m, 1H), 7.65 (d, J = 7.0 Hz, 2H), 7.49 (d, J = 2.0 Hz, 1H), 7.45 (t, J = 8.0 Hz, 2H), 7.29 (d, J = 2.0 Hz, 1H), 7.21 (d, J = 7.0 Hz, 2H), 7.14−7.19 (m, 1H), 7.08 (t, J = 9.5 Hz, 1H), 6.80 (t, J = 2.5 Hz, 1H), 6.76 (t, J = 2.5 Hz, 1H), 5.62 (d, J = 6.0 Hz, 1H), 5.57 (d, J = 6.0 Hz, 1H), 4.95−5.00 (m, 2H), 4.51 (t, J = 7.0 Hz, 2H), 2.14−2.50 (m, 2H), 1.93−2.01 (m, 2H). 19F NMR (470 MHz, d6-DMSO): δ = −67.32 (d, J = 711.11 Hz, 6F), −109.64 to −109.61 (m, 1F), −111.48 to −111.45 (m, 1F), −119.86 to −119.83 (m, 1F), −121.75 to −121.72 ppm (m,1F). MS Calcd: m/z 919.2 for [M − PF6] (C40H30F4IrN10), found: m/z 919.2. Anal. Calcd for C40H30F10IrN10P: C, 45.16; H, 2.84; N, 13.17. Found: C, 45.24; H, 2.95; N, 13.08. 2.3. Electrochemical Measurements. Cyclic voltammetry (CV) was performed on a BAS 100 W instrument with a scan rate of 100 mV s−1 in acetonitrile using tetrabutylammonium hexafluorophosphate

(0.1 M) as the supporting electrolyte and ferrocene as the internal standard. The analytic system adopted the three-electrode configuration with a glassy carbon electrode as the working electrode, an aqueous saturated calomel electrode as the operating reference electrode, and a platinum wire as the counter electrode.

3. RESULTS AND DISCUSSION The synthesis and characterization of Ir(III) complex B1 have been described previously by our group.6 Similar to B1, other complexes were prepared in high yields via the reaction of organometalated dimer 1-(2,4-difluorophenyl)-1H-pyrazole (dfppz) with 2.2 equiv of the corresponding ancillary ligands in 1,2-ethanediol at 150 °C for 12 h, followed by an ionexchange reaction from Cl− to PF6−. Complexes B1, G1, Y1, and O1 can be easily soluble in common organic solvents such as CH3CN, CH2Cl2, THF, and DMF. Their absorption spectra in CH3CN solution with a concentration of 10−5 M are recorded at room temperature (see Figure S1 in the Supporting Information). The intense absorption bands below 350 nm correspond to the spin-allowed π−π* transition of the ligands, while the weak bands that extend into the visible region can be assigned to excitations to spin-allowed and spin-forbidden metal-to-ligand charge transfer (MLCT) as well as ligand-to-ligand charge transfer (LLCT).7 Upon photoexcitation, all complexes are almost nonemissive in the dilute solutions, as shown in Figure 1a. Usually, the

Figure 1. Photographic images of solution, nanoparticles (a) and neat films (b) for complexes B1, G1, Y1, and O1. (c) Emission spectra of B1, G1, Y1, and O1 in neat films.

nonemissive metal-centered (3MC) state plays an important role for the luminescent behavior of a heavy-metal complex. If the nonradiative deactivation pathway from the lowest triplet excited state (T1) to 3MC, followed by 3MC to 3MC/S0 crossing point, is accessible at room temperature, the obtained phosphors will be nonluminescent (see Figure S2).8 However, the calculated results suggest that they exhibit similar deactivation energy profiles via 3MC states and undergo a C

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Organometallics relatively high barrier for the T1−3MC conversion (Table S1). We tendentiously attribute the origin of the nonemission behavior in solution to their intrinsic excited-state character of intraligand charge transfer and more nonradiatively decay channels.9 However, in sharp contrast, their nanoaggregation and neat films exhibit strong luminescence, indicating that the aggregation turns on the light. Such different emission behaviors between dilute solutions and aggregation states suggest the AIE activity.10 As the results indicate, the luminescent colors of studied complexes are highly dependent on the structures of ancillary ligands, with the emission maximum ranging from 499 to 555 nm. The detailed photophysical characteristics are summarized in Table S2. B1 exhibits bright blue-green emission with the lifetime of 1.09 μs in neat film. When the methyl group of B1 is replaced by a stronger electron-rich trifluoromethyl (CF3) unit, the distinctly red-shifted emission for complex G1 (507 nm) is observed. On the other hand, if the carbazole moieties in both B1 and G1 were further modified by two methyl groups, the emissions of resulting complexes Y1 and O1 also exhibit significant bathochromic shift compared with those of B1 and G1, respectively. The emission spectrum of Y1 (534 nm) in neat film is blue-shifted with respect to O1 (555 nm). Putting all the emission data together enables us to draw a clear overall picture for their emission behaviors (Figure 2). As shown in

Figure 3. (a) CV curves of complexes B1, G1, Y1, and O1 and (b) their electronic density contours of HOMOs and LUMOs.

(HOMO) energy level. It explains why G1 shows a much redshifted emission spectrum than B1. The similar phenomenon is observed in the case of Y1 and O1 when compared with their CV curves. Furthermore, compared with complex B1, the oxidation potentials for Y1 that has the same acceptor, but different functional donor, on the ancillary ligand are shifted cathodically by (10 mV). The destabilized HOMO and similar lowest unoccupied molecular orbitals (LUMOs) energy levels result in red-shifted emission for Y1. As can be seen in Figure 3a, it is clearly noted that the studied complexes with the same donor and acceptor unit in the ancillary ligands exhibit almost identical oxidation and reduction potentials, respectively. This is further validated by the theoretical calculations. Figure 3b depicts their atomic orbital composition of HOMOs and LUMOs along with the energy evolution. It is clear that B1 and G1 (Y1 and O1) show similar HOMOs energy levels, respectively, which agrees well with the CV data. The similar LUMOs energy levels are also found for B1 and Y1 as well as G1 and O1, as shown in Figure 3b. According to the experimental and theoretical results, it is demonstrated that the LUMOs energies can be significantly stabilized by introducing a strong electron-withdrawing moiety into the acceptor unit on ancillary ligands. Weakening the ability of the donor unit will lead to much stabilized HOMOs energy level. On the basis of this principle, the energy gaps and emission colors of AIE-active Ir(III) complexes would be ingeniously controlled. To verify this supposition, another cationic iridium(III) complex with AIE property, G2, has been designed and prepared (Figure S3). G2 has the same donor but stronger acceptor moiety (pyridine−tetrazole unit) in ancillary ligands compared with that of B1. Comparing the structural characters of B1 and G2, it is expected that G2 will exhibit bright green emission in the aggregation state. The experiment data undoubtedly confirm

Figure 2. Schematic illustration for the effect of donor and acceptor strength on the emission behaviors of the studied system.

Figure 2, the ancillary ligands could be divided into two groups: one is a triazole−pyridine unit as an acceptor, whereas the other is a carbazole-based functional moiety as a donor. When the strength of the acceptor and/or donor units is increased, the different degrees of bathochromic shift in emissions are observed and vice versa. It is well-known that the emission behavior is directly related to the frontier molecular orbital energy level. The electrochemical behaviors of each complex and theoretical calculations have been performed to further understand the effect of the substituent group on the energy level changes. Their electrochemical characteristics were determined by cyclic voltammetry (see Figure 3), and the data are listed in Table S2. Each complex exhibits a reversible ligand-based reduction peak and a nearly reversible oxidation potential. As shown in Figure 3, substitution of the methyl group in B1 by an electron-donating CF3 on the acceptor results in an obvious decrease in the reduction potential from −2.00 V for B1 to −1.82 V for G1. Nevertheless, the oxidation potential of B1 (0.68 V) is almost identical to that of G1 (0.70 V), implying that B1 and Y1 should possess a similar highest occupied molecular orbital D

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4. CONCLUSIONS In summary, we successfully designed and synthesized a series of Ir(III)-based AIE materials to investigate the relationship between the structure and emission color. The color can be modulated efficiently by controlling the ability of the donor and/or acceptor in ancillary ligands. Enhancing the strength of either donor or acceptor leads to red-shifted emission as such changes in the structures adjust the HOMO and LUMO levels, respectively, supported by the theoretical and electrochemical data. The control experiments further confirm this issue. The significant ML behavior is also observed. The new design strategy reported here is facile and would offer a generic and effective way for developing phosphorescent AIE materials with tunable emission properties.

our expectation, and G2 shows the emission maximum of 518 nm. Recent reports indicate that the emission colors of some AIE materials in solid states can be modulated by external stimuli.11 The intrinsic high efficiency of AIE materials in aggregation states makes them promising candidates for such stimuliresponsive emission color switching materials. Among them, pressure-responsive materials, also termed as mechanochromic luminescent (ML) materials, are of importance for practical applications as the mechanical stimulus such as grinding and shearing is facile to be handled.11b,12 However, phosphorescent ML materials are less investigated. The new molecule structures and in-depth understanding of the structure−mechanochromism relationship are helpful for the development of efficient phosphorescent ML materials. Herein, we found that as-prepared powder G1 (G1-A) shows strong blue light with the emission maximum at 452 nm (see Figure 4). Interestingly,

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00788. Syntheses of ligands, supplemental schemes, figures, and theoretical calculations (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (G.-G.S.). *E-mail: [email protected] (Z.-M.S.). ORCID

Zhong-Min Su: 0000-0002-3342-1966

Figure 4. Emission spectra of G1 in various states. G1-A, G1-G, and G1-F represent as-prepared, ground, and fuming samples, respectively.

Notes

The authors declare no competing financial interest.

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by grinding G1-A, the emission color was largely red-shifted to green, exhibiting obvious ML behavior. The green emission can perfectly return to its original blue light with treatment of the ground sample using ether. Supported by the previous works, the PXRD data (Figure S4) suggest that the ML behavior for G1 is attributed to the interconversion between crystalline and amorphous states. As shown in Figure 5, the potential

ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (21303012, 21273030, 51203017, 21131001, and 60937001), the 973 Program (2013CB834801), and the Science and Technology Development Planning of Jilin Province 20130204025GX.

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REFERENCES

(1) (a) Fan, C.; Yang, C. Chem. Soc. Rev. 2014, 43, 6439−6469. (b) Costa, R. D.; Orti, E.; Bolink, H. J.; Monti, F.; Accorsi, G.; Armaroli, N. Angew. Chem., Int. Ed. 2012, 51, 8178−8211. (c) Ulbricht, C.; Beyer, B.; Friebe, C.; Winter, A.; Schubert, U. S. Adv. Mater. 2009, 21, 4418−4441. (d) You, Y.; Nam, W. Chem. Soc. Rev. 2012, 41, 7061−7084. (e) Chi, Y.; Chou, P. T. Chem. Soc. Rev. 2010, 39, 638− 655. (f) Schneider, G. E.; Bolink, H. J.; Constable, E. C.; Ertl, C. D.; Housecroft, C. E.; Pertegàs, A.; Zampese, J. A.; Kanitz, A.; Kessler, F.; Meier, S. B. Dalton Trans. 2014, 43, 1961−1964. (2) (a) Zhao, Q.; Li, F.; Huang, C. Chem. Soc. Rev. 2010, 39, 3007− 3030. (b) Zhao, Q.; Huang, C.; Li, F. Chem. Soc. Rev. 2011, 40, 2508− 2524. (3) (a) Luo, J.; Xie, Z.; Lam, J. W. Y.; Cheng, L.; Chen, H.; Qiu, C.; Kwok, H. S.; Zhan, X.; Liu, Y.; Zhu, D.; Tang, B. Z. Chem. Commun. 2001, 1740−1741. (b) Ding, D.; Li, K.; Liu, B.; Tang, B. Z. Acc. Chem. Res. 2013, 46, 2441−2453. (c) Mei, J.; Hong, Y.; Lam, J. W. Y.; Qin, A.; Tang, Y.; Tang, B. Z. Adv. Mater. 2014, 26, 5429−5479. (4) (a) You, Y.; Huh, H. S.; Kim, K. S.; Lee, S. W.; Kim, D.; Park, S. Y. Chem. Commun. 2008, 3998−4000. (b) Zhao, Q.; Li, L.; Li, F.; Yu, M.; Liu, Z.; Yi, T.; Huang, C. Chem. Commun. 2008, 685−687. (c) Huang, K.; Wu, H.; Shi, M.; Li, F.; Yi, T.; Huang, C. Chem. Commun. 2009, 1243−1245.

Figure 5. Reversible writing−erasing process based on complex G1.

application of G1 for optical recording is demonstrated, in which the letter “S” is easily recorded and subsequently erased with ether. Another letter, “Z”, can be easily rewritten. It is noted that G1 exhibits more significant ML behavior in comparison with B1.6 Thereby, we speculate that the simple modulation of strength of donor and/or acceptor controls not only the emission of Ir(III)-based AIE materials but also their ML properties. It is ongoing work in our laboratory. E

DOI: 10.1021/acs.organomet.6b00788 Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.organomet.6b00788 Organometallics XXXX, XXX, XXX−XXX