Excited-state properties and photosensitization behaviour of bis(2,4-dihydroxyphenyl)squaraine

Kamat, Prashant V. ; Hotchandani, Surat ; Lind, Michael de. ; Thomas, George K. ; Das, Suresh ; George, M. V. (1993) Excited-state properties and photosensitization behaviour of bis(2,4-dihydroxyphenyl)squaraine Journal of Chemical Society, Faraday Transactions, 89 (14). pp. 2397-2402. ISSN 0956-5000

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Official URL: http://www.rsc.org/publishing/journals/FT/article....

Related URL: http://dx.doi.org/10.1039/FT9938902397


Two protonation equilibria (pKa at 3.7 and 7.4) have been identified for the dye, bis(2,4-dihydroxyphenyl)-squaraine in the ground state. These various protonation forms exhibit widely different absorption properties. The singlet excited-state behaviour of this dye has been characterized by picosecond laser flash photolysis. The fluorescence quantum yield and the excited singlet lifetime of the unprotonated dye (φf= 0.092, Ts= 740 ps) are considerably higher than that of the neutral (φf= 0.037, Ts= 130 ps) or the protonated (φf= 0.01, Ts≤ 100 ps) forms of the dye. The triplet excited state has been characterized by both direct excitation and T-T energy transfer methods. The triplet excited state has an absorption maximum around 430 nm and a lifetime of ca. 100 μs in ethanol. Photosensitization of a thin microporous TiO2 semiconductor film has been carried out by adsorbing the squaraine dye from an ethanolic solution and exciting it with visible light. An incident photon-to-current conversion efficiency of 0.05% at 500 nm has been obtained for the dye-modified TiO2 electrode.

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