PHOTOINDUCED ELECTRON-TRANSFER FROM (ALKOXYPHENYL)TRIPHENYLPORPHYRINS TO INTERFACE WATER OF AEROSOL DIOCTYL- AND CETYLTRIMETHYLAMMONIUM BROMIDE/ALCOHOL REVERSE MICELLES AT 77 K

Photoinduced electron transfer from (alkoxyphenyl)triphenylporphyrins (CnOPTPP) to the interface water of anionic aerosol dioctyl- (AOT) and cationic cetytrimethylammonium bromide/alcohol (CTAB/ROH) reverse micelles at 77 K produces paramagnetic (alkoxyphenyl)triphenylporphyrin cation radical (CnOPTPP+). The photoproduced radicals are identified and quantitated with electron spin resonance by measuring the g factor, hyperfine splitting, and the doubly integrated spectrum. The photoproduced radical yields are correlated with the deuterium modulation depth of CnOPTPP+ by electron spin-echo modulation (ESEM), which measures changes in the interaction distance of the porphyrin cation headgroup with water (D2O) at the reverse micelle interface as a function of C-n alkyl chain length. The location of the porphyrin cation headgroup relative to interface water (D2O) is controlled by the alkyl chain length of CnOPTPP,the cosurfactant alcohol and the headgroup charge of the surfactant forming the reverse micelle. A longer alkyl chain decreases the photoyield because of increased hydrophobic interaction between CnOPTPP and the surfactant alkyl chains of the reverse micelles which ''pulls'' the porphyrin moiety more into the alkane region of the reverse micelles. This is directly monitored by a decreasing deuterium modulation depth with increasing alkyl chain length of COPTPP. The photoyield also decreases by changing the cosurfactant alcohol of the cationic CTAB/ROH reverse micelles from 1-butanol to 1-octanol due to decreasing hydrophilicity as the alcohol chain length increases which is confirmed by ESEM data on the degree of interface-water interaction. Also, the amount of radical conversion of CnOPTPP+ to surfactant alkyl and cosurfactant alcohol radicals decreases from 1-butanol to 1-octanol which decreases the net photoyield. Finally, the cationic interface charge of CTAB/ROH reverse micelles gives a higher photoyield than anionic AOT reverse micelles which reflects micelles which reflects electron transfer across the interface to achieve net photoionization. This is partly mitigated by a shorter distance of the porphyrin moiety to the interface in AOT versus CTAB/ROH reverse micelles as shown by ESEM data.