The pore structure of zeolite Y consists of 13 Å supercages connected through 7 Å windows. This study deals with the intrazeolitic photoelectron transfer from trisbipyridyl ruthenium (II) (Ru(bpy) 3 2+ ) synthesized within zeolite Y supercages to ion-exchanged bipyridinium molecules in neighboring supercages. Three N,N′-dialkyl-2,2′-bipyridinium ions and a 4,4′-bipyridinium ion with reduction potentials varying from -0.37 to -0.65 V have been studied. For the 2,2′-bipyridinium salts (members of the diquat family), two, three, and four CH 2 bridging units abbreviated as 2DQ 2+ , 3DQ 2+ , and 4DQ 2+ , respectively, have been examined. The fourth viologen is 1,1′-dimethyl-4,4′-bipyridinium, commonly known as methyl viologen and abbreviated here as MV 2+ . Because of the limitations of the time-resolved diffuse reflectance instrument, only a lower limit of the forward electron transfer rate constant from Ru(bpy) 3 2+ * to the bipyridinium ion was obtained and is >10 7 s -1 . The back electron transfer from the photogenerated bipyridinium radical ions to Ru(bpy) 3 3+ was monitored at different intrazeolitic bipyridinium concentrations. At low loadings of bipyridinium ions (1 per 10-15 supercages), the transient signal between 360 and 390 nm has contributions from both Ru(bpy) 3 2+ * and the bipyridinium radical ions, since the bipyridinium ion concentration was not high enough to quench all of the Ru(bpy) 3 2+ *. The decay of this signal (360-390 nm) could be fitted to the sum of two exponentials, representing the disappearance of unquenched Ru(bpy) 3 2+ * and the back electron transfer from the bipyridinium radical ions to Ru(bpy) 3 3+ . The rate constants for the back electron transfer for 2DQ 2+ , MV 2+ , 3DQ 2+ , and 4DQ 2+ were found to be 4.0 × 10 4 , 1.7 × 10 4 , 1.1 × 10 4 , and 7.3 × 10 3 s -1 . The decrease in the electron transfer rates with increasing driving force for the reaction indicates that the electron transfer is occurring in the Marcus inverted region. At high loadings of the bipyridinium ions (1.2-1.7 molecules/supercage), the bipyridinium radical ions were considerably longer lived, and a simple exponential decay no longer described the loss of the bipyridinium radical signal. A model that allows for electron exchange processes between bipyridinium ions to compete with the back electron transfer was necessary. This kinetic model allowed us to extract the back electron transfer rate at high loadings along with the rate constants for electron hopping and a second-order electron (bipyridinium radical)/hole (Ru(bpy) 3 3+ ) recombination process. For the series 2DQ 2+ , MV 2+ , 3DQ 2+ , and 4DQ 2+ with high loading, the back electron transfer rate constants were 2.5 × 10 5 , 9 × 10 4 , 1.8 × 10 5 , and 1.2 × 10 5 s -1 , higher than the low loading samples. In the high loading case, longer lived charge separation was observed because of the presence of a route for charge propagation by electron hopping via the densely packed viologen molecules.Practical solar energy conversion processes, such as the p...

Photochemical studies of molecules in the organized voids of microporous frameworks is an area of considerable research interest. In this study, we have examined the spectroscopy and photochemistry of trans-azobenzene introduced into the 8 Å channels of an aluminophosphate framework, AlPO4-5. The acidity of aluminophosphates is considered to be very weak, based on their poor catalytic performance in transformations of organic compounds. However, we report that the Brönsted acidity of the AlPO4-5 is enough to protonate the azo groups in azobenzene. This leads to appearance of a band at 418 nm. Also, room temperature emission observed at 518 nm, an unusual spectroscopic feature for azobenzene, is due to the protonated form. Photolysis of the azobenzene/AlPO4-5 sample leads to the formation of benzo[c]cinnoline and benzidine. The Lewis acid sites of AlPO4-5 are proposed to play an important role in the photocyclization chemistry. Because the number of such acid sites in AlPO4-5 is limited, only a fraction of the azobenzene molecules undergo photocyclization. The rest exhibit reversible cis−trans photoisomerization in the presence of visible and ultraviolet irradiation.