A series of anils (1−6) have been incorporated in NaY zeolites and the resulting samples characterised spectroscopically. Raman spectral analysis showed that anils exist in the zeolite microcavities predominantly in a zwitterionic form. In agreement, diffuse reflectance UV/Vis spectra showed the presence of a significant concentration of the zwitterionic form, characterised by an absorption band around 400 nm. A sharp contrast is drawn between their photochemistry in solution or in the crystalline form with that in NaY zeolites. Thus, steady state irradiation at 400 nm led to persistent changes in the diffuse reflectance UV/Vis spectra with decrease of the reflectance of the band at 400 nm and the appearance of a new absorption band at longer wavelengths. No photochromism is observed and this is attributed to the isomerization [a]

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The electrochemical response of open/closed forms of 6-nitro-1‘,3‘,3‘-trimethylspiro[2H-1-benzopyran-2,2‘-indoline] (SP) associated with zeolite Y (SP@Y) and MCM-41 silicates with or without framework Al (SP@AlMCM and SP@MCM, respectively) is described upon immersion of zeolite-modified polymer film electrodes into MeCN using LiClO4, Et4NClO4, and Bu4NPF6 as supporting electrolytes. These samples show a reverse photochemical behavior, the open form undergoing ring closure to the closed one upon illumination with visible light (λ > 450 nm). Oxidation processes at +1.10 and +0.80 V vs AgCl (3 M NaCl)/Ag, corresponding to open and closed SP, respectively, exhibit a significant reversibility, suggesting that post-electron-transfer reactions resulting in the apparently irreversible voltammetry observed in solution are highly hindered here. Reduction of all boundary-associated SP forms occurs in two reversible one-electron steps involving the nitrobenzene group. Upon irradiation, SP@Y shows a remarkable site-selective electrocatalytic effect on the oxidation of N,N,N‘,N‘-tetramethylbenzidine (TMB) in Et4NClO4 and LiClO4 electrolytes. Rotating disk voltammetry indicates that the rate-determining step can be attributed to the formation of a surface adduct between TMB and closed SP associated with the zeolite boundary. The value of the second-order rate constant of this process is 2.2 × 105 L/(mol s) in 0.10 M Et4NClO4/MeCN.