Intriguing Indium-salen Complexes as Multicolor Luminophores

*E-mail for Y.K.: [email protected]., *E-mail for K.M.L.: ... systematically bathochromic shifts, depending on the electronic modification of the be...
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Intriguing Indium-salen Complexes as Multicolor Luminophores Seon Hee Lee,†,⊥ Nara Shin,‡,⊥ Sang Woo Kwak,§ Kyunglim Hyun,§ Won Hee Woo,§ Ji Hye Lee,‡ Hyonseok Hwang,‡ Min Kim,§ Junseong Lee,∥ Youngjo Kim,*,§ Kang Mun Lee,*,‡ and Myung Hwan Park*,† †

Department of Chemistry Education, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon, Gangwon 24341, Republic of Korea § Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea ∥ Department of Chemistry, Chonnam National University, Gwangju 61186, Republic of Korea ‡

S Supporting Information *

ABSTRACT: The series of novel salen-based indium complexes (3-tBu-5-R-salen)In-Me (3-tBu-5-R-salen = N,N′-bis(2-oxy-3-tert-butyl-5-R-salicylidene)-1,2-diaminoethane, R = H (1), tBu (2), Br (3), Ph (4), OMe (5), NMe2 (6)) and [(3-tBu-5-NMe3salen)In-Me](OTf)2 (7; OTf = CF3SO3−) have been synthesized and fully characterized by NMR spectroscopy and elemental analysis. All indium complexes 1−7 are highly stable in air and even aqueous solutions. The solid-state structures for 3−5, which were confirmed by single-crystal X-ray analysis, exhibit square-pyramidal geometries around the indium center. Both the UV/vis absorption and PL spectra of 1−7 exhibit significant intramolecular charge transfer (ICT) transitions based on the salen moieties with systematically bathochromic shifts, which depend on the introduction of various kinds of substituents. Consequently, the emission spectra of these complexes cover almost the entire visible region (λem = 455−622 nm).

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INTRODUCTION Fluorescent/phosphorescent organometallic complexes have been widely used as efficient functional materials in organic light-emitting diodes (OLEDs) and photovoltaic cells because of their outstanding optical properties and high thermal stability.1−6 The luminescent properties of these luminophores can be controlled by a systematic modulation of the ligand frameworks. The incorporation of various substituents into the ligand as a scaffold for transition-metal complexes can induce fascinating photophysical properties, such as emission color tuning and quantum efficiency modifications, leading to an expansion of their use as promising luminescent materials.7−9 In particular, organometallic complexes based on group 13 metals such as aluminum and gallium have been recently reported as prominent optoelectronic materials due to their excellent electronic and photophysical properties.10−13 Since the first discovery of tris(8-hydroxyquinolinato)aluminum (Alq3) by Tang and VanSlyke in 1987,14 a wide range of aluminum-based complexes as prominent optoelectronic materials have been developed.11,15−23 In a continuous effort to explore a novel class of color-tunable luminophores, we investigated salen-based indium complexes, which are heavier congener systems of well-known luminescent Al-salen complexes.24,25 To the best of our knowledge, there have been no reported studies on monomeric indium complexes that display multicolor emission features due to the simple alteration of their substituents. Therefore, we have prepared a series of indium-based complexes with salen ligands and investigated © XXXX American Chemical Society

the fundamental nature of the emissions induced by these complexes in detail.

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RESULTS AND DISCUSSION Synthesis and Characterization. The synthesis of (3-tBu5-R-salen)In-Me complexes (1−6) based on ligands L1−L6 is shown in Scheme 1. The salen-type ligands L1−L6 were analogously synthesized, according to previously reported procedures.22,23 The indium luminophores 1−6 were obtained in high yield (63−86%) by the reaction of InMe3 precursors with the respective salen ligands in toluene. InCl3 and InMe3 could be applied to the synthesis of salenbased indium complexes; however, InMe3 was more convenient from the aspects of mild reaction conditions and better yield with no side product. InCl3 gave inseparable mixtures of reaction products. Additionally, the di-ionic complex 7 was readily produced by methylation of the NMe2 substituents in the neutral complex 6 with an excess of MeOTf (Scheme 1, 95%). Although the neutral complexes 1−6 showed high solubility in common organic solvents such as THF, toluene, and chloroform, the di-ionic complex 7 was only soluble in polar MeCN and DMSO. Importantly, in contrast to group 13 based salen complexes such as Al-salen complexes with Al−Me bonds,23,26 complexes 1−7 with In−Me bonds were highly stable in air and Received: November 21, 2016

A

DOI: 10.1021/acs.inorgchem.6b02797 Inorg. Chem. XXXX, XXX, XXX−XXX

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(red, 6), which covered the entire visible region (Figure 2b). Importantly, complex 7, which was produced by methylation of the NMe2-appended 6, exhibited a considerable emission shift of 167 nm, which is similar to the previous results obtained for Al-salen complexes.23 These optical findings are correlated with the respective Hammett constants27 except for 3 and 4; this is similar to what was observed in other complexes.23 The orders of the emission and absorption maxima for all of the complexes were identical. More importantly, the emission spectra of 1−7 clearly exhibited bathochromic shifts with increasing solvent polarity, which indicate the presence of polarized excited states for all of the complexes (Figures S9 and S10 in the Supporting Information). In addition to the broad nature of the emission spectra, these results also revealed that the emission features originated from salen-centered intramolecular charge transfer (ICT) transitions.23 Most importantly, due to the observation of multicolor emission through substituent variation and electronic modification at the benzene ring in 1−7, the indium complexes could be considered a novel class of luminophores. Furthermore, the emission spectra of 1−7 in the solid state showed emission features that were comparable to those obtained in solution (Figure S11 in the Supporting Information). The fluorescence quantum efficiency (Φem) of these complexes was in the range of 0.10−0.36, which is similar to those of Al-based luminophores23 except for 6 (Φem = 0.01) and 7 (Φem = 0.09). Moreover, the emission decay lifetime, measured as 0.20−1.1 ns in 1−7, revealed that the emissions of all the indium complexes were fluorescent (Figure S12 in the Supporting Information). Electrochemical Properties. Cyclic voltammetry (CV) measurements were performed to get the electrochemical properties for the In-salen complexes 1−7 (Figure S13 in the Supporting Information). While complex 6 underwent reversible oxidation, complexes 1−5 and 7 exhibited quasi-reversible oxidation processes. The measured oxidation potentials and, thus, the calculated HOMO energy levels for 1−7 largely depended on the electron-donating ability at the benzene ring (Table 1). Consequently, there was a tendency for the HOMO levels for all complexes to be destabilized as the electrondonating effect of benzene ring gradually increased. Theoretical Calculations. To clarify the nature of the electronic transitions and multicolor emission features of 1−7, time-dependent density functional theory (TD-DFT) calculations (Figures S14−S20 and Tables S3−S16 in the Supporting Information) on the ground state (S0) and the first singlet excited state (S1, Figure 3) optimized structures of all complexes were performed with the B3LYP/6-31G(d) basis sets. To check the effects of the THF solvent, the conductorlike polarizable continuum model (CPCM) was also used.28,29 The calculation results for 1−7 in the S0 state showed that the

Scheme 1. Synthetic Routes for Indium Complexes 1−7, Containing Modified salen Ligands

even aqueous solutions, which were definitely confirmed by 1 H NMR experiments for 3 and 4 in THF-d8 with D2O (THF/ D2O (v/v) = 4/1) (Figure S1 in the Supporting Information). Compounds 1−7 were fully characterized by 1H and 13 C NMR spectroscopy (Figures S2−S8 in the Supporting Information) and elemental analysis. In particular, the 1H NMR spectra of 1−7 clearly showed two multiplets at ca. 3.9 and 3.7 ppm, which correspond to ethylene bridge protons (−CH2CH2−), indicating the complete formation of a tetradentate [N2O2] coordination between indium(III) and the salen moiety. In addition, a specific singlet peak attributed to In−CH3 protons was clearly detected in 1−7 at ca. −0.3 ppm. The carbon signals corresponding to In−CH3 were observed only in 1 (1.00 ppm), 2 (−0.01 ppm), and 3 (5.13 ppm), despite the prolonged acquisition times. Furthermore, the molecular solid-state structures for 3−5 (Figure 1 and Tables S1 and S2 in the Supporting Information) revealed that the bond between indium and the methyl group was nearly perpendicular to the tetradentate plane of the indium center, which indicates a square-pyramidal geometry around the In center. It was clearly demonstrated that the values of the trigonality parameter (τ) for 3−5 are as 0.28, 0.18, and 0.12, respectively. Photophysical Properties. To get the optical data for complexes 1−7, UV/vis absorption and photoluminescence (PL) experiments were performed in THF solution (Table 1 and Figure 2). Major absorption bands from 360 to 424 nm, which are attributed to π−π* transitions in the salen moiety, were observed, and other salen-based transition-metal complexes have shown similar absorption trends.23 Among the complexes, the absorption maximum (λabs = 360 nm) of the cationic NMe3-appended complex 7 was observed in the highest energy region. Accordingly, the absorption maxima of these complexes typically displayed a gradual red shift as the electron-donating effect of substituents at the benzene ring increased. The PL spectra of 1−7 were observed from 455 (blue, 7) to 622 nm

Figure 1. X-ray crystal structures of 3 (left), 4 (center), and 5 (right) (50% thermal ellipsoids). For clarity, the H atoms and diethyl ether molecules (for 4) are omitted. B

DOI: 10.1021/acs.inorgchem.6b02797 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. Photophysical Data for 1−7 λem/nm compound 1 2 3 4 5 6 7

λabsa/nm (log ε) 363 375 382 388 402 424 360

(4.24) (4.16) (4.01) (4.10) (4.10) (3.78) (4.18)

λex/nm

cyclohexaneb

THFb

DMSOb

solid

Φema,c

Voxd/V

HOMOe/eV

τobsa/ns

371 376 377 388 403 432 362

473 482 477 502 481 595 450

476 484 486 502 521 622 455

479 486 491 503 525 625 459

473 479 481 497 499 574 456

0.24 0.36 0.15 0.28 0.10 0.01 0.09

0.50 0.48 0.38 0.33 0.19 −0.13 0.53

−5.30 −5.28 −5.18 −5.13 −4.99 −4.67 −5.35

0.86 1.1 0.66 1.1 1.1 0.20 1.0

c = 1.0 × 10−5 M in THF. bc = 1.0 × 10−5 M, determined at 298 K. cQuinine sulfate (Φ = 0.55) used as a standard. dThe oxidation onset potential in DMSO (c = 5.0 × 10−4 M, scan rate 100 mV s−1) with reference to the ferrocene/ferrocenium (Fc/Fc+) redox couple. eCalculated from Eox. a

Furthermore, on the basis of the theoretical results for the S1-optimized structures of all the complexes, the major contribution to low-energy emission involved the HOMO-1 → LUMO transition, except for 6 (HOMO → LUMO+1 transition) and 7 (HOMO → LUMO transition) (Table 2 and Figure 3), indicating the presence of ICT features attributed to salen-centered π−π* transitions; this was identical with the phenomena observed for the S0-optimized structures of 1−7. Indeed, the broad and intense low-energy emission bands were also clearly observed in the solid state (Figure S11 in the Supporting Information). In addition, while the C5 substituents contribute considerably to the HOMO-1 (1−5) or HOMO (6 and 7), the LUMO (1−5 and 7) or LUMO+1 (6) exhibited negligible contributions at the benzene ring moiety. Notably, the order (7 > 1 > 2 > 3 > 4 > 5 > 6) of the computed lowestenergy emission maxima was in complete agreement with that of the experimentally observed emission bands (Table 1). From these results, we were convinced that the introduction of various kinds of substituents in the salen ligand chelated to indium affects the HOMO or HOMO-1 energy levels, which can systematically modulate their fluorescence color.

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CONCLUSION We have synthesized and fully characterized novel monomeric indium-salen complexes 1−7 with various substituents at the benzene ring. These In complexes were highly stable in air and aqueous solutions. The UV/vis absorption and PL spectra of 1−7 revealed salen-centered ICT transitions with gradual bathochromic shifts depending on substituent modification and electronic effects at the benzene ring, as supported by theoretical calculations. In particular, the emission spectra of all complexes cover the entire visible region (λem = 455−622 nm). Ongoing efforts are underway to develop versatile indium-salen complexes as promising optoelectronic materials.

Figure 2. (a) UV/vis absorption and (b) PL spectra in THF (1.0 × 10−5 M) for 1−7. The inset gives the emission color observed under a hand-held UV lamp (λex = 365 nm).

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largest contribution (f > 0.7) to low-energy absorptions was predominantly associated with the electronic transition from the HOMO-1 to LUMO (Figure S21 in the Supporting Information). The HOMO-1 for all of the complexes was mainly localized on the benzene ring moieties (89−93%) containing C5 substituents, whereas the LUMO was distributed over the bridging imine group (53−56%) and benzene ring moieties (43−47%). These findings indicate that low-energy electronic transitions for 1−7 originate from π−π* electronic transitions based on salen moieties with a substantial ICT character between the benzene ring moieties and bridging imine groups, similar to those observed in salen-based Al complexes.23 This feature was in agreement with the broad absorption bands observed for the In-salen complexes 1−7.

EXPERIMENTAL SECTION

General Considerations. All air- and moisture-sensitive operations were carried out under an atmosphere of dinitrogen by using standard Schlenk line and glovebox techniques.30,31 All commercially available chemicals were purchased from Aldrich and Alfa Aesar and used as supplied without any further purification. All solvents were passed through an activated alumina column and stored over activated molecular sieves (5 Å). Deuterated solvents such as CDCl3, CD3CN, and THF-d8 (Cambridge Isotope Laboratories) were used after storing over activated molecular sieves (5 Å). Measurements. 1H and 13C NMR analyses were performed at ambient temperature on a 400 MHz NMR spectrometer using standard parameters. All chemical shifts are reported in ppm referenced to the signals of residual CDCl3 (δ 7.24 for 1H NMR; δ 77.0 for 13C NMR) or CD3CN (δ 1.94 for 1H NMR; δ 1.32 and 118.26 for 13C NMR). C

DOI: 10.1021/acs.inorgchem.6b02797 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 3. Frontier molecular orbitals for 1−7 at their first excited singlet state (S1) with their relative energies from DFT calculation (isovalue 0.04). The transition energy (in nm) was calculated using the TD-B3LYP method with 6-31G(d) basis sets. a 20 mL toluene solution of salen ligands L1−L6 (0.5 mmol) at room temperature. The reaction mixture was stirred for 12 h, and then the solvent was removed in vacuo. The crude product was washed with n-hexane (50 mL), and then drying in vacuo afforded the desired products 1−6. Data for 1 (R = H): ivory solid (0.18 g, 70%). 1H NMR (CDCl3): δ 8.18 (s, 2H), 7.32 (d, J = 8.0 Hz, 2H), 6.91 (d, J = 8.0 Hz, 2H), 6.54 (t, J = 12.0 Hz, 2H), 3.86 (m, 2H), 3.70 (m, 2H), 1.45 (s, 18H), −0.30 (s, 3H, In−CH3). 13C NMR (CDCl3): δ 170.75, 169.97, 143.07, 132.90, 131.32, 119.41, 114.26, 55.42, 35.36, 29.38, 1.00 (In−CH3). Anal. Calcd for C25H33InN2O2: C, 59.07; H, 6.54; N, 5.51. Found: C, 58.62; H, 6.19; N, 5.28. Data for 2 (R = tBu): pale yellow solid (0.27 g, 86%). 1H NMR (CDCl3): δ 8.24 (s, 2H), 7.39 (d, J = 4.0 Hz, 2H), 6.86 (d, J = 4.0 Hz, 2H), 3.89 (m, 2H), 3.67 (m, 2H), 1.45 (s, 18H), 1.27 (s, 18H), − 0.32 (s, 3H, In−CH3). 13C NMR (CDCl3): δ 170.88, 168.06, 142.28, 135.88, 129.49, 128.24, 118.10, 55.50, 35.57, 33.84, 31.39, 29.46, −0.01 (In−CH3). Anal. Calcd for C33H49InN2O2: C, 63.87; H, 7.96; N, 4.51. Found: C, 63.55; H, 8.13; N 4.37. Data for 3 (R = Br): pale yellow solid (0.27 g, 81%). 1H NMR (CDCl3): δ 8.06 (s, 2H), 7.34 (d, J = 4.0 Hz, 2H), 7.01 (d, J = 4.0 Hz, 2H), 3.86 (m, 2H), 3.72 (m, 2H), 1.41 (s, 18H), −0.28 (s, 3H, In−CH3). 13C NMR (CDCl3): δ 169.82, 168.72, 145.67, 134.36, 134.18, 120.54, 105.79, 55.34, 35.61, 29.15, 5.13 (In−CH3). Anal. Calcd for C25H31Br2InN2O2: C, 45.07; H, 4.69; N, 4.21. Found: C, 44.83; H, 4.50; N 4.14. Data for 4 (R = Ph): pale yellow solid (0.28 g, 85%). 1H NMR (CDCl3): δ 8.30 (s, 2H), 7.61 (d, J = 4.0 Hz, 2H), 7.51 (d, J = 8.0 Hz, 4H), 7.38 (t, J = 12.0 Hz, 4H), 7.24 (t, J = 16.0 Hz, 2H), 7.16 (d, J = 4.0 Hz, 2H), 3.93 (m, 2H), 3.77 (m, 2H), 1.52 (s, 18H), −0.23 (s, 3H, In−CH3). 13C NMR (CDCl3): δ 170.92, 169.61, 143.43, 141.29, 130.92, 130.69, 128.65, 127.07, 126.24, 126.00, 119.33, 55.47, 35.57, 29.45. Anal. Calcd for C37H41InN2O2: C, 67.28; H, 6.26; N, 4.24. Found: C, 67.35; H, 5.97; N, 3.97. Data for 5 (R = OCH3): yellow solid (0.15 g, 65%). 1H NMR (CDCl3): δ 8.12 (s, 2H), 7.02 (d, J = 4.0 Hz, 2H), 6.34 (d, J = 4.0 Hz, 2H), 3.84 (m, 2H), 3.72 (m, 2H), 3.72 (s, 6H), 1.44 (s, 18H), −0.33 (s, 3H, In−CH3). 13C NMR (CDCl3): δ 170.17, 165.36, 148.32, 144.70, 121.85, 117.72, 112.35, 55.78, 55.50, 35.54, 29.29. Anal. Calcd for C27H37InN2O4: C, 57.05; H, 6.56; N, 4.93. Found: C, 56.64; H, 6.94; N, 4.49. Data for 6 (R = N(CH3)2): orange solid (0.19 g, 63%). 1H NMR (CDCl3): δ 8.20 (s, 2H), 7.10 (d, J = 4.0 Hz, 2H), 6.35 (d, J = 4.0 Hz, 2H), 3.85 (m, 2H), 3.69 (m, 2H), 2.77 (s, 12H), 1.45 (s, 18H),

Table 2. Major Low-Energy Electronic Transitions for 1−7 at Their First Excited Singlet State (S1) Calculated using the TD-B3LYP Method with 6-31G(d) Basis Setsa 1 2 3 4 5 6 7

λcalc/nm

fcalc

assignment

438.73 451.33 454.46 463.85 513.97 530.41 418.75

0.0154 0.0180 0.0174 0.0685 0.0170 0.0647 0.0882

HOMO-1 → LUMO (99.1%) HOMO-1 → LUMO (99.3%) HOMO-1 → LUMO (99.2%) HOMO-1 → LUMO (97.8%) HOMO-1 → LUMO (99.4%) HOMO → LUMO+1 (89.4%) HOMO → LUMO (98.0%)

a

Singlet energies for the vertical transition calculated at the optimized S1 geometries.

An EA3000 (Eurovector) analyzer, Jasco V-530 spectrophotometer, and Spex Fluorg-3 Luminescence spectrophotometer were used to obtain elemental analyses, UV/vis spectra, and photoluminescence spectra, respectively. Emission decay lifetime curves were obtained by a time-correlated single-photon counting (TCSPC) spectrometer (FLS920, Edinburgh Instruments) equipped with a microchannel plate photomultiplier tube (MCP-PMT, 200−850 nm) as a detector at room temperature and an EPL-375 ps pulsed semiconductor diode laser as an excitation source. The lifetimes were calculated by exponential curve fittings. Cyclic voltammetry measurements using an AUTOLAB/ PGSTAT12 system were investigated in DMSO (0.5 mM) with a three-electrode cell configuration (Pt working and counter electrodes and a Ag/AgNO3 (0.1 M in MeCN) reference electrode) at room temperature. Tetrabutylammonium hexafluorophosphate (nBu4PF6, 0.1 M in DMSO) as a supporting electrolyte was used. The oxidative potentials were observed at a scan rate of 100 mV s−1 and measured with reference to the Fc/Fc+ redox couple. Synthesis. 3-tert-Butyl-5-R-2-hydroxybenzaldehyde (R = Br, Ph, OMe, NMe2),32−35 salen ligands L1−L6,36 and InMe3 were synthesized from the reaction between InCl3 and 3.5 equiv of MeLi in THF at −78 °C using literature procedures.37 After 1 h, all volatiles were removed under vacuo. Recrystallization from hexane gave InMe3 as a colorless crystalline solid (Figure S22 in the Supporting Information). Caution! Since solid InMe3 is a highly pyrophoric material, its careful manipulation is required. Solid InMe3 should be stored and must be handled under an inert atmosphere. General Synthesis of (3-tBu-5-R-salen)In-Me (1−6). A 10 mL toluene solution of InMe3 (90 mg, 0.55 mmol, 1.1 equiv) was added to D

DOI: 10.1021/acs.inorgchem.6b02797 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry −0.34 (s, 3H, In−CH3). 13C NMR (CDCl3): δ 170.54, 164.72, 143.71, 140.46, 123.39, 118.21, 116.46, 55.54, 43.10, 35.65, 29.39. Anal. Calcd for C29H43InN4O2: C, 58.59; H, 7.29; N, 9.42. Found: C, 58.86; H, 7.00; N, 9.17. Synthesis of [(3-tBu-5-NMe3-salen)In-Me](OTf)2 (7). An excess of MeOTf (0.058 g, 0.35 mmol, 3.5 equiv) was added to a 20 mL dichloromethane solution of 6 (0.060 g, 0.10 mmol) at room temperature. The reaction mixture was stirred for 0.5 h and the insoluble parts were removed by the filtration. Additional washing of insoluble filtrate with dichloromethane (2 × 10 mL) followed by drying in vacuo afforded 7 as a colorless solid (0.088 g, 95%). 1 H NMR (CD3CN): δ 8.44 (s, 2H), 7.50 (d, J = 4.0 Hz, 2H), 7.47 (d, J = 4.0 Hz, 2H), 4.02 (m, 2H), 3.82 (m, 2H), 3.49 (s, 18H, N(CH3)3), 1.46 (s, 18H), −0.21 (s, 3H, In−CH3). 13C NMR (CD3CN): δ 171.98, 170.52, 145.95, 134.57, 125.14, 122.94, 119.46, 58.10, 55.94, 36.94, 29.52. Anal. Calcd for C33H49InN4O8S2F6: C, 42.96; H, 5.35; N, 6.07. Found: C, 42.53; H, 5.71; N, 5.64. X-ray Crystallography. The slow diffusion method of Et2O into a solution of 3−5 in THF was used to get single crystals of 3−5 suitable for X-ray crystallographic analyses. The obtained crystals of 3−5 were coated with Paratone oil to maintain the crystallinity of complexes and mounted onto the end of a glass capillary. A Bruker D8QUEST CCD area detector diffractometer with Mo Kα (λ = 0.71073 Å) radiation was used for the crystallographic measurements. The structures were solved by using direct methods, and all non-hydrogen atoms were subjected to anisotropic refinement by a full-matrix least-squares method F2 using the SHELXTL/PC program package,38 giving crystallographic data of 3−5 in CIF format (CCDC 1498540−1498542). Hydrogen atoms were geometrically calculated by the refinement of corresponding C atoms with isotropic thermal parameters. The details of crystallographic data for 3−5 are presented in Tables S1 and S2 in the Supporting Information. UV/Vis Absorption and Photoluminescence (PL) Measurements. The measurements of UV/vis absorption were carried out in degassed THF with a 1 cm quartz cuvette (1.0 × 10−5 M). PL measurements were measured in various degassed solvents, such as THF, cyclohexane, and dimethyl sulfoxide (1.0 × 10−5 M), and in the solid state at ambient temperature. The solution quantum yields were calculated with reference to that of quinine sulfate (0.5 M H2SO4, Φ = 0.55).39 Theoretical Calculations. The optimized structures on the ground state (S0) and first excited state (S1) of 1−7 were obtained by the density functional theory (DFT) method with the B3LYP functional40,41 and 6-31G(d)42 basis sets. Electronic transition states, energies, and electron correlation were obtained from time-dependent DFT measurements (TD-DFT)43 with the hybrid B3LYP functional. All calculated data for 1−7 were conducted in THF, and the solvent effects were estimated with the conductor-like polarizable continuum model (CPCM).28,29 All calculations were performed by the GAUSSIAN 09 program.44 The GaussSum 3.0 application was used to obtain the contributed percentage of each molecular orbital.45

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ORCID

Youngjo Kim: 0000-0001-8571-0623 Author Contributions ⊥

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF2015R1D1A1A01057396 for K.M.L.) and the Ministry of Science, ICT & Future Planning (NRF-2016R1C1B1008452 for M.H.P.). Y.K. and M.K. thank the NRF through the Creative Human Resource Training Project for Regional Innovation (NRF-2014H1C1A1066874).

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* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02797. Computational, and spectroscopic data and 1H and 13C data (PDF) Crystallographic details (CIF) Crystallographic details (CIF) Crystallographic details (CIF)

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These authors contributed equally.

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*E-mail for Y.K.: [email protected]. *E-mail for K.M.L.: [email protected]. *E-mail for M.H.P.: [email protected]. E

DOI: 10.1021/acs.inorgchem.6b02797 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.6b02797 Inorg. Chem. XXXX, XXX, XXX−XXX