Novel iridium(III) complexes based on 2-(2,2′-bithien-5-yl)-quinoline. Synthesis, photophysical, photochemical and DFT studies

Four novel cyclometalated iridium(III) complexes: [Ir(q-bt-Ph)(2)(phen)]PF6, [Ir(q-bt-Ph)(2)(acac)], [Ir(q-bt-Me)(2)(bpy)]PF6 and [Ir(q-bt-Me)(2)(acac)] (where q-bt-Ph, q-bt-Me correspond to 2-(2,2'-bithien-5-yl)-4-phenylquinoline and 2-(2,2'-bithien-5-yl)-4-methylquinoline), are reported. The complexes were characterized by NMR, FTIR and HRMS. The optical, electrochemical properties and thermal stability of novel iridium(III) complexes were thoroughly investigated. The complexes emit a light in the narrow range of 693-707 nm. The optical study showed that replacement of fragment in the main quinoline ligand did not affect wavelength of the emitted light. On the other hand, the modification of the ancillary ligand and substituent in the quinoline ring caused the increase of the photoluminescence quantum yields. Electrochemical experiments demonstrate that the oxidation process for complexes [Ir(q-bt-Ph)(2)(phen)]PF6 and [Ir(q-bt-Ph)(2)(acac)] was reversible (or quasi-reversible) and well detectable whereas for complexes with quinoline substituted by methyl group was irreversible, even at low temperature (-70 degrees C). The electrochemical and photophysical studies have been Well confirmed by density functional theory (DFT) calculations. In addition, bulk heterojunction polymer solar cells based on complexes [Ir(q-bt-Ph)(2)(phen)]PF6 and [Ir(q-bt-Ph)(2)(acac)] were fabricated. Only the solar cell incorporating [Ir(q-bt-Ph)2(acac)] exhibited a photovoltaic effect. The architecture of the cell was ITO/PEDOT:PSS/P3HT:PCBM: [Ir(q-bt-Ph)(2)(acac)]/Al. A power conversion efficiency of 0.25% was measured under 1 sun illumination using an AM 1.5G filter to simulate the solar spectrum. (C) 2015 Elsevier B.V. All rights reserved.