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 (CnPtPP) 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 (CC4, CHCl3, CH2Cl2, or CH3CH2CH2Cl) as electron accepters. CnPtPP (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 CnPtPP. The relative photoyield of the porphyrin cation radical (CnPtPP+) measured by ESR decreased in the order DODAC > DPPC > DHP. The addition of CCl4, CHCl3, CH2Cl2, or CH3CH2CH2Cl into C9PtPP/DHP vesicles enhanced the C9PtPP+ radical photoyield. All four chloroalkanes acted as better electron accepters in competition with water at the vesicle interface. The results are discussed in terms of the alkyl chain length of CnPtPP, the vesicle surface charge, and the effects of chloroalkanes as electron accepters.