A Carbazole‐Containing Difunctional Ru II 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 ] – · [N(C 4 H 9 ) 4 ] + (where Hecip = 2‐(9‐ethyl‐9 H ‐carbazol‐3‐yl)‐1 H ‐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 1 H 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 TiO 2 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.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)