DOI: 10.17344/acsi.2016.2246 Acta Chim. Slov. 2016, 63, 323-326 323 Scientific paper New Iridium Complex Coordinated with Tetrathiafulvalene Substituted Triazole-pyridine Ligand: Synthesis, Photophysical and Electrochemical Properties Zhi-Gang Niu, Hui Xie, Li-Rong He, Kai-Xiu Li, Qing Xia, Dong-Min Wu, Gao-Nan Li* College of Chemistry and Chemical Engineering, Hainan Normal University, Haikou 571158, PR China * Corresponding author: E-mail: ligaonan2008@163.com, niuzhigang1982 @ 126.com Received: 13-01-2016 Abstract A new iridium(III) complex based on the triazole-pyridine ligand with tetrathiafulvalene unit, [Ir(ppy)2(L)]PF6 (1), has been synthesized and structurally characterized. The absorption spectra, luminescent spectra and electrochemical behaviors of L and 1 have been investigated. Complex 1 is found to be emissive at room temperature with maxima at 481 and 510 nm. The broad and structured emission bands are suggested a mixing of 3LC (3n-n*) and 3CT (3MLCT) excited states. The influence of iridium ion coordination on the redox properties of the TTF has also been investigated by cyclic voltammetry. Keywords: Iridium(III) complexes; Tetrathiafulvalene; Triazole-pyridine ligands; Photoluminescence; Cyclic voltam-metry 1. Introduction For several decades, tetrathiafulvalene (TTF) and its derivatives were extensively developed by scientists in photofunctional materials1-8 because of their strongly electron-donating and attractive reversible redox properties. As a consequence, a large synthetic effort has also been devoted to the preparation of materials that exhibit synergy or coexistence between conductivity and luminescence. Coordination of TTF-containing ligands to transition metal centers is typically achieved by functio-nalizing TTF with nitrogen atom.9 Very recently, we have reported a new nitrogen-containing TTF-based ligand, 2-(1-(2-((4',5'-bis(methylthio)-[2,2'-bi(1,3-dithiolylidene)]-4-yl)thio)ethyl)-1H-1,2,3-triazol-4-yl)pyridine (L). Ligand L was used as the polyp- prtppirfcClh (l=lf N UIHKjPFi PI'S Scheme 1. Synthetic routes of Ir(III) complex 1. Niu et al.: New Iridium Complex Coordinated with Tetrathiafulvalene . 326 Acta Chim. Slov. 2016, 63, 323-326 yridine NAN ligand and binap/xantphos as diphosphines PAP ligand to form two Cu(I) complexes, [Cu(I)(Binap) (L)]BF4 and [Cu(I)(Xantphos)(L)]BF4, which exhibited advantageous electrochemical and photophysical properties.10 The results hence led us to further design other metal complexes based on the TTF-containing thioethyl-bridged triazole-pyridine ligand. Iridium(III) complexes have widely been employed in organic light-emitting devices (OLEDs), as they have high phosphorescence quantum efficiency, long excited-state lifetime and excellent color tenability.11-14 Therefore, the association of the redox-active TTF unit with cyclo-metalated iridium(III) complex is intriguing in coordination chemistry and material chemistry. In this work, we report the synthesis of a new bis-cyclometallated TTF-ba-sed iridium(III) complex with ppy as CAN ligand, [Ir(ppy)2(L)]PF6 (1) (Scheme 1). Their electrochemical and photophysical properties are also investigated. 2. Experimental 2. 1. Materials and Measurements 2-(1-(2-((4',5'-bis(methylthio)-[2,2'-bi(1,3-dithioly-lidene)]-4-yl)thio)ethyl)-1#-1,2,3-triazol-4-yl)pyridine (L) was synthesized in our previous work,8 and an improved preparation method was used to synthesize the cyclo-metalated iridium chlorobridged dimer [Ir(ppy)2Cl]2 in good yield.15 All solvents were dried using standard procedures. Solvents used for electrochemistry and spectros-copy were spectroscopic grade. 1H NMR and 13C NMR spectra were recorded on a Bruker AM 400 MHz instrument. Chemical shifts were reported in ppm relative to Me4Si as internal standard. FT-IR spectra were taken on a Nicolet 6700 FTIR spectrometer (400-4000 cm-1) with KBr pellets. ESI-MS spectra were recorded on an Esquire HCT-Agilent 1200 LC/MS spectrometer. The elemental analyses were performed on a Vario EL Cube Analyzer system. UV-vis spectra were recorded on a Hitachi U3900/3900H spec-trophotometer. Fluorescence spectra were carried out on a Hitachi F-7000 spectrophotometer. 2. 2. Synthesis of [Ir(ppy)2(L)]PF6 (1) A mixture of a dimer [Ir(ppy)2Cl]2 (50 mg, 46.5 pmol) and L (58 mg, 93.0 pmol) was dissolved in 6 mL of DCM and MeOH (v/v = 1 : 1) and refluxed for 6 h under nitrogen. The orange-red solution was then cooled to room temperature and NH4PF6 (38 mg, 0.23 mmol) was added to the solution. The mixture was stirred at room temperature for 4 h, and then evaporated to dryness. The solid was purified by column chromatography with DCM/MeOH (100 : 1) eluent to afford pure product 1 (54 mg, Yield: 50.5 %) as a yellow solid. 1H NMR (400 MHz, CDCl3): 5 9.04 (s, 1H), 8.27 (d, J = 8.0 Hz, 1H), 7.99 (t, J = 73.6 Hz, 1H), 7.90-7.92 (m, 2H), 7.82 (d, J = 4.2 Hz, 1H), 7.65-7.79 (m, 6H), 7.53 (d, J = 5.6 Hz, 1H), 6.88-7.08 (m, 6H), 6.40 (d, J = 7.2 Hz, 1H), 6.31 (d, J = 6.8 Hz, 1H), 5.97 (s, 1H), 4.63 (t, J = 6.0 Hz, 2H), 3.12-3.15 (m, 2H), 2.42 (s, 6H). 13C NMR (100 MHz, CDCl3): 5 168.2, 167.6, 150.0, 149.9, 149.7, 149.5, 148.7, 148.5, 146.2, 143.8, 143.7, 139.7, 138.1, 138.0, 132.0, 131.9, 130.7, 130.2, 129.1, 127.9, 127.1, 126.6, 126.3, 124.8, 124.5, 123.5, 123.1, 122.8, 122.6, 121.6, 119.5, 119.4, 114.5, 108.9, 49.6, 34.8, 29.7; ESI-MS (m/z): 1001.0 [M-PF6]+. IR (cm-1): v = 3442 (m), 2922 (w), 2853 (w), 1608 (m), 1475 (m), 1422 (m), 1265 (w), 1100 (w), 842 (s), 756 (m), 556 (w). Anal. calcd. For C39H32F6IrN6PS7: C 40.86, H 2.81, N 7.33; found: C 40.95, H 2.96, N 7.45. 2. 3. Cyclic Voltammetry Cyclic voltammetry (CV) was performed on a CHI 1210B electrochemical workstation, with a glassy carbon electrode as the working electrode, a platinum wire as the counter electrode, an aqueous saturated calomel electrode (SCE) as the reference electrode, and 0.1 M n-Bu4NClO4 as the supporting electrolyte. 3. Results and Discussion 3. 1. Photophysical Properties 3. 1. 1. Absorption Properties The absorption spectra of L and 1 in dichlorometha-ne solution at room temperature are depicted in Fig. 1. For ligand L and complex 1, these strong absorption bands at a high energy (À < 350 nm) are assigned to spin-allowed intraligand (tc^tc*) transitions of TTF-TzPy ligand (L) or ancillary ligand (ppy). The moderate absorption bands at lower energy (350-450 nm) correspond to intramolecular charge-transfer transition (ICT) for L16 and metal-to-li-gand charge-transfer (MLCT, dn(Ir)^n*(L)) transition for 1, respectively.17,18 3. 1. 2. Emission Properties The relative emission spectra of ligand L and complex 1 in degassed CH2Cl2 solution at room temperature are also given in Fig. 1. Upon excitation at 438 nm, complex 1 displays two intense emission maxima at ca. 481 and 510 nm. As for L, the emission band occurs at about 462 nm (^ex = 363 nm). Therefore the vibronically structured emission of 1 is probably derived from a mixing of 3LC (3n-n*) and 3CT (3MLCT) excited states.19,20 3. 2. Electrochemical Properties The electrochemical behaviors of the ligand L and iridium complex 1 were investigated by cyclic voltamme- Niu et al.: New Iridium Complex Coordinated with Tetrathiafulvalene . 326 Acta Chim. Slov. 2016, 63, 323-326 Wavelength i Fig. 1: UV and FL spectra of ligand L and complex 1 in CH2Cl2 try in CH2Cl2 solution (Fig. 2 and Table 1). Both compounds (L and 1) exhibit two reversible one-electron oxidation processes, which are associated with the successive oxidation of the TTF unit to TTF+ and TTF2+. Additionally, complex 1 show a irreversible oxidation peak (Epox) at 1.88 V, which is attributed to the metal-centered Ir3+/Ir4+ oxidation couple.21,22 In comparison with the ligand L, the two oxidation waves for complex 1 are shifted to more negative potentials. The observed results are different from the previous reported work,23 it is possible that the tria-zole-pyridine unit is grafted on the TTF core through a non-conjugated spacer group, which is disadvantageous to intramolecular electron transfer and communications.10 Table 1: Redox potentials of ligand L and complex 1 Compounds E^OV " E,22(V) " Ep0K (Ir3+/4+) (V) L 0.57 0.91 - 1 0.48 0.87 1.88 aE 1/2 = 1/2(Epa + Epc), where E and Epc are the anodic and catho-dic peak potentials, respectively. Fig. 2: Cyclic voltammograms for ligand L and complex 1 in CH2Cl2 solution containing n-Bu4NClO4 (0.1 M) at a sweep rate of 100 mV/s 4. Conclusions In conclusion, a new iridium(III) complex 1 based on tetrathiafulvalene-substituted triazole-pyridine ligand, has been synthesized and fully characterized by 1H NMR, 13C NMR, mass spectrometry, FTIR and elemental analyses. The photophysical and electrochemical properties have been measured and analyzed. The luminescent spectra show that the emissive state originates from mixed intrali-gand and metal-to-ligand charge transfer 3(n^n* + MLCT) transitions. The electrochemical studies reveal that 1 undergo reversible TTF/TTF+/TTF2+ redox processes and one irreversible Ir3+^Ir4+ oxidation process. The research plays a role in designing new photoelectric functional materials, and more work is going on in our laboratory. 5. Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 21501037), the Natural Science Foundation of Hainan Province (No. 20152031) and Hainan Provincial Innovation Experiment Program for University Students (No. 201511658002). 6. Supplementary Material 1H NMR, 13C NMR and ESI-MS spectra for iridium complex 1. 7. References 1. M. Bendikov, F. Wudl, D. F. Perepichka, Chem. Rev. 2004, 104, 4891-4945. http://pubs.acs.org/doi/abs/10.1021/cr030666m 2. S. Wenger, P. A. Bouit, Q. L. Chen , J. Teuscher, D. D. Censo, R. H. Baker, J. E. 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Chem. 2011, 696, 3076-3085. http://www.sciencedirect.com/science/article/pii/S0022328 X11003676 Povzetek Sintetiziran in strukturno okarakteriziran je nov iridijev(III) kompleks [Ir(ppy)2(L)]PF6 (1) z vezanim triazol-piridin-skim ligandom modificiranim s tetratiafulvensko skupino. Absorpcijski in luminiscenčni spekter ter elektrokemijske lastnosti L in 1 so bili raziskani. Kompleks 1 emitira pri sobni temperature pri 481 in 510 nm. Široki in strukturirani emisijski trakovi so pripisani mešanju 3LC (3n-n*) in 3CT (3MLCT) vzbujenih stanj. Vpliv koordinacije iridijevega iona na redoks lastnosti TTF skupine je bil raziskan s pomočjo ciklične voltametrije. Niu et al.: New Iridium Complex Coordinated with Tetrathiafulvalene . New Iridium Complex Coordinated with Tetrathiafulvalene Substituted Triazole-pyridine Ligand: Synthesis, Photophysical and Electrochemical properties Zhi-Gang Niu, Hui Xie, Li-Rong He, Kai-Xiu Li, Qing Xia, Dong-Min Wu, * Gao-Nan Li* College of Chemistry and Chemical Engineering, Hainan Normal University, Haikou 571158, PR China * Corresponding author: E-mail: ligaonan2008@163.com, niuzhigang1982@126.com Supplementary Information 1H NMR of Iridium Complex 1 0 9.5 9,'ci a.5 S.'o ' 7.'5 7.'« 6,'i (j!o 5'a ' 5.0 4.'i 4.'tl 3.5 3'0 ' 2^5 2.0 l.'a 1.0 (1! 5 0.0 -CI fl M 13 C NMR of Iridium Complex 1 ESI-MS of Iridium Complex 1