Photoionization of N-alkylphenothiazines with different alkyl chain lengths in mesoporous silicoaluminophosphate molecular sieves with different pore sizes

Abstract

The photoionization of N-alkylphenothiazines (PCn where n = 1, 6, 10 and 18) in mesoporous silicoaluminophosphate (UHM-3) molecular sieves with three different pore sizes has been studied by electron spin resonance (ESR) at room temperature. N-alkylphenothiazines were synthesized with three alkyl chain lengths (n = 6, 10 and 18). Mesoporous calcined UHM-3 molecular sieves with three different pore sizes of 1.9, 2.9 and 3.8 nm were prepared with n-dodecyltrimethylammonium or n-hexadecyltrimethylammonium chlorides and with 1,3,5-trimethylbenzene (TMB) as an auxiliary organic additive. N-alkylphenothiazines were incorporated into these mesoporous silicoaluminophosphates by impregnation and were photoionized at room temperature to form stable N-alkylphenothiazine cation radicals (PCn+) whose photoyields were measured by ESR. The highest photoyields are obtained for PC6 in C-12-UHM-3 (1.9 nm pore), PC10 in C-16-UHM-3 (TMB/A1 = 1) (2.9 nm pore) and PC18 in C-16-UHM-3 (TMB/A1 = 3) (3.8 nm pore). The yield of PC18 increases with increasing pore size which correlates with faster decays of the photoproduced cation radicals in smaller pores. (C) 2001 Published by Elsevier Science B.V.