A Triphenylamine-Grafted Imidazo4,5-f1,10phenanthroline Ruthenium(II) Complex: Acid−Base and Photoelectric Properties

A new heteroleptic ruthenium (II) complex of Ru (Hipdpa) (Hdcbpy) (NCS) (2) (-). 0. 5H (+). 0. 5N (C (4) H (9) ) (4) (+) Ru (Hipdpa) where Hdcbpy = monodeprotonated 4, 4'-dicarboxy-2, 2'-bipyridine and Hipdpa = 4- (1H-imidazo4, 5-f1, 10phenanthrolin-2-yl) -N, N-diphenylaniline was synthesized and characterized by elementary analysis, standard spectroscopy techniques, and cyclic voltammetry. The ground- and excited-state acid-base properties of Ru (Hipdpa) were studied by means of UV-vis absorption spectrophotometric and spectrofluorimetric titrations in 4: 1 (v/v) Britton-Robinson/dimethylformamide buffer solution. The four-step separate protonation/deprotonation processes were found in the ground states, and one of which taking place near the physiological pH range. The two observable excited-state protonation/deprotonation processes were found for the Ru (Hipdpa), constituting pH-induced "off-on-off" emission switches. The performance of the complexes as photosensitizers in nanocrystalline TiO (2) -based liquid solar cells containing an electrolyte solution (0. 05 M I (2), 0. 5 M LiI, and 0. 5 M 4-tert-butylpyridine in 50% acetonitrile and 50% propylene carbonate) was investigated and found to achieve a much improved device performance (a short-circuit photocurrent density of 18. 7 mA cm (-2), an open-circuit voltage of 630 mV, and an overall conversion efficiency of 6. 85%) compared to a triphenylamine-free parent complex Ru (Hpip) (Hdcbpy) (NCS) (2) (-). N (C (4) H (9) ) (4) (+) -based device Hpip = 2-phenyl-1H-imidazo4, 5-f1, 10phenanthroline and a comparable performance to that of cis-bis (isothiocyanato) bis (2, 2'-bipyridine-4, 4'-dicarboxylic acid) ruthenium (II) (N3) under identical experimental conditions. A density functional theory calculation of the molecular structures and electronic properties of the complexes was also carried out in an effort to understand their effectiveness in TiO (2) -based solar cells.