Electron paramagnetic resonance and diffuse reflectance spectroscopic studies of the photoionization of N-alkylphenothiazines in synthetic microporous M-clinoptilolite (M = Na+ + K+, H+, Li+, Na+, K+, Ni2+, Co2+, Cu2+) molecular sieves at room temperature

Authors:
Publisher website
Google Scholar
Abstract
Methylphenothiazine and other N-alkylphenothiazines were incorporated into M-clinoptilolite (M=Na++K+, H+, Li+, Na+, K+, Ni2+, Co2+, Cu2+) channels by impregnation. Photoionization of N-alkylphenothiazines (PCn) doped into dehydrated M-clinoptilolite samples at room temperature by ultraviolet irradiation results in the formation of N-alkylphenothiazine radical cations (PCn•+). The radicals were identified by the electron paramagnetic resonance (EPR) g-factor and by diffuse reflectance spectroscopy. Dehydrated M-clinoptilolites are efficient hosts for the formation and stabilization of PCn+ at room temperature. As-synthesized M-clinoptilolite that was not dehydrated and then doped with PCn was EPR silent. The PCn+ yield was determined by double integration of the EPR spectrum. The PCn+ yield is highest in H-clinoptilolite among the other ion-exchanged M-clinoptilolites. The photoionization efficiency to form PCn+ decreases in the order H-clinoptilolite>Ni-clinoptilolite>K-clinoptilolite>Na-clinoptilolite>Co-clinoptilolite>Na,K-clinoptilolite>Li-clinoptilolite>Cu-clinoptilolite. The photooxidation yields decrease as the PCn alkyl chain length increases from methylphenothiazine (PC1) to decylphenothiazine (PC10). The photoionization efficiency depends on the nature of the metal ion and the channel size of the M-clinoptilolite material.