Location and photoionization studies of a series of alkylporphyrin derivatives solubilized in dioctadecyldimethylammonium chloride and dihexadecyl phosphate vesicles

Abstract

Light-induced electron transfer reactions in micelles and vesicles solutions have been extensively investigated with the aim of optimizing the net conversion of light energy into chemical energy. Three alkylporphyrins were synthesized, 5-(1-nonylpyridinium-4-yl)-10,15,20-triphenylporphyrin bromide (H[sub 2]PC[sub 9]), 5-(1-dodecylpyridinium-4-yl)-10,15,20-triphenylporphyrin bromide (H[sub 2]PC[sub 12]), and 5-(1-hexadecylpyridinium-4-yl)-10,15,20-triphenylporphyrin bromide (H[sub 2]PC[sub 16]). The location of these 5-(1-alkylpyridinium-4-yl)-10,15,20-triphenylporphyrin bromides (H[sub 2]PC[sub n]) solubilized in cationic dioctadecyldimethylammonium chloride (DODAC) and anionic dihexadecyl phosphate (DHP) vesicles solutions was investigated using optical absorption spectroscopy. Electron spin resonance (ESR) was applied to observe the yields of photoionization of H[sub 2]PC[sub n] in rapidly frozen DODAC and DHP vesicle solutions versus alkyl chain length. A decrease in photoyield correlated with a increase in the porphyrin-to-vesicle interface distance. The photoionization of H[sub 2]PC[sub n] in rapidly frozen DODAC and DHP vesicle solutions containing electron acceptors was also studied by ESR. Two different electron acceptors were used in this study, tetrabromobenzoquinone (TBBQ) and potassium ferricyanide (K[sub 3]Fe(CN)[sub 6]). Electron transfer within the vesicle itself was examined with TBBQ, which solubilizes inside the lipophilic region of the vesicle near the interface, whereas K[sub 3]Fe(CN)[sub 6] involved electron transfer across the vesicle interface. The yields of photoionization of H[sub 2]PC[sub n] have generally been foundmore » to decrease upon addition of either acceptor. The results are discussed in terms of alkyl chain length, position of the porphyrin group relative to the vesicle interface, and vesicle surface charge.« less