A new water-soluble perylene diimide derivative, N,N'-bis(12-sulfoaminododecyl)-3,4,9,10-perylenetetracarboxdiimide (SULFAPER), has been synthesized and characterized by visible, fluorescence, IR, H-1 and C-13 NMR, mass, CV and time resolved measurements. Its photophysical properties in aqueous and organic solutions have been described. The singlet energy levels of the synthesized compound have been found to be 57.8 kcal/mol and 59.2 kcal/mol in aqueous and methanol solution, respectively. The LUMO energy level of SULFAPER has been determined by solid state cyclic voltammetry, and found to be -3.60 eV. SULFAPER undergoes two electron reduction process (-0.64 V and -0.42 V) versus ferrocene. SULFAPER has an energy band gap of 2.56 eV. The absorption maximum of the synthesized compound gives bathochromic shift of 12 nut in water with respect to its visible spectrum in methanol solution. The fluorescence quantum yields of the compound are low both in water and methanol solution because of the aggregation effect. Time-resolved fluorescence measurements have showed that the fluorescence decay times of the SULFAPER are tau(1) = 4.1 ns and tau(2) = 0.8 ns in water, and tau(1) = 4.0 ns and tau(2) = 2.5 ns in methanol solutions. The aqueous solution of SULFAPER is stable under UV-VIS irradiation, but a slight loss of fluorescence emission (25%) has been detected at a rate of k(p) = 6.3 x 10(-5) s(-1) in methanol solution, which might be the result of either the quenching of fluorescence emission by reactive oxygen species, or by enhanced aggregation effect. SULFAPER-sensitized photooxidations of (E)-cinnamic acid and methyl acrylate have been found to give selective photoproduct formations under concentrated sun light in organic phase. (E)-cinnamic acid has been seen to favor photochemical E-Z isomerization and methyl acrylate has been seen to favor the formation of methyl 2-oxopropanoate. The quantum yield of (E)-cinnamic acid (Phi(CA)) under concentrated solar irradiation process has been calculated to be about 0.015, by the employment of an actinometry method developed by Erten and Icli. (c) 2005 Elsevier Ltd. All rights reserved.