A Carbazole-Containing Difunctional RuII Complex That Functions as a pH-Induced Emission Switch and an Efficient Sensitizer for Solar Cells

A heteroleptic ruthenium(II) complex of [Ru(Hecip)(Hdcbpy) (NCS)(2)](-)center dot[N(C4H9)(4)](+) (where Hecip = 2-(9-ethyl-9H-carbazol-3-yl)-1H-imidazo[4,5-f][1,10]phenanthroline and Hdcbpy = monodeprotonated 2,2'-bipyridyl-4,4'-dicarboxylic acid) has been synthesized and characterized by elementary analysis, cyclic voltammetry, MALDI-TOF mass spectrometry, and H-1 NMR, IR, UV/Vis absorption, and emission spectroscopy. The ground- and excited-state acid-base properties of the complex have been studied by means of UV/Vis absorption spectrophotometric and spectrofluorimetric titrations in a Britton-Robinson/DMF (v/v, 4:1) buffer solution. The complex was found to act as pH-induced off -on-off/on-off-on-off-type emission switch, when excited at 530/470 nm, with a protonation/deprotonation reaction taking place near the physiological pH range. The performance of the complex-sensitized TiO2 nanocrystalline solar cell with 0.05 M I-2 and 0.5 M LiI in 50 % acetonitrile and 50 % propylene carbonate (PC) as the electrolyte solution and a platinum film as the counter electrode has also been studied, and was compared to that of the cis-[Ru(H(2)dcbpy)(2)(NCS)(2)] (N3)-sensitized solar cell under the same experimental conditions. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)