Photoionization of (p-Alkylphenyl)triphenylporphyrins in Neutral and Positively and Negatively Charged Vesicles:  Effects of Alkyl Chain Length and Addition of Chloroalkanes

The photoionization of ( p -alkylphenyl)triphenylporphyrins (C n PtPP) in cationic dioctadecyldimethylammonium chloride (DODAC), neutral dipalmitoylphosphatidylcholine (DPPC), and anionic dihexadecyl phosphate (DHP) frozen vesicles has been studied by electron spin resonance (ESR) with visible light irradiation at 77 K with and without addition of chloroalkanes (CCl 4, CHCl 3, CH 2 Cl 2, or CH 3 CH 2 CH 2 Cl) as electron acceptors. C n PtPP ( n = 3, 6, 9, and 12) were synthesized and used to study the effects of alkyl chain length. The photoionization efficiency was found to decrease with increasing alkyl chain length of C n PtPP. The relative photoyield of the porphyrin cation radical (C n PtPP + ) measured by ESR decreased in the order DODAC > DPPC > DHP. The addition of CCl 4, CHCl 3, CH 2 Cl 2, or CH 3 CH 2 CH 2 Cl into C 9 PtPP/DHP vesicles enhanced the C 9 PtPP + radical photoyield. All four chloroalkanes acted as better electron acceptors in competition with water at the vesicle interface. The results are discussed in terms of the alkyl chain length of C n PtPP, the vesicle surface charge, and the effects of chloroalkanes as electron acceptors.