6533b82efe1ef96bd1293ca7

RESEARCH PRODUCT

Ship-in-a-Bottle Synthesis of a Large Guest Occupying Two Y Zeolite Neighbour Supercages: Characterisation and Photocatalytic Activity of the Encapsulated Bipyrylium Ion

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In a series of papers we reported the ship-in-a-bottle synthesis, photochemical properties and photocatalytic applications of 2,4,6-triphenylpyrylium cation (TP ) encapsulated inside the cavities of large pore zeolites Y and Beta. 2] The identity of encapsulated TP was then confirmed spectroscopically, particularly by the match of the IR spectra of the encapsulated organic material and that of the tetrafluoroborate solid of TP (TPBF4). In addition, the electrochemical response of zeolite Y encapsulated TP (TP@Y) consisted of a reversible single reduction process taking place at the same redox potential as that measured for TPBF4 solutions. Encapsulation of TP has a dramatic influence on its photophysical and photochemical properties. Thus it was shown that TP@Y emits phosphorescence at room temperature, exhibits a delayed fluorescence emission and has a long-lived (hundreds of s) triplet excited state. These properties of TP@Y are remarkably different from those exhibited by TP in solution, wherein no room temperature phosphorescence or delayed emission are observed. In addition, the lifetime of the excited state in solution is much shorter lived (a few s). Noteworthy is the fact that, upon illumination of an aqueous suspension of TP@Y, hydroxyl radicals are generated; this capability of TP@Y to generate OH . in water can be exploited in photocatalysis. In this context, it appears to be potentially interesting to explore the photocatalytic properties of related pyrylium dyes. Following these previous studies, herein we report the synthesis, characterisation, electrochemical properties and photocatalytic activity of 1,4-bis(3,5-diphenyl-4-pyrylium)phenylene, commonly known as bipyrylium (BTP ), encapsulated inside the cavities of zeolite Y. By considering the reported molecular modelling for TP inside zeolite Y and the fact that BTP is an even larger molecule, it is obvious that BTP can not be accommodated inside a single zeolite Y supercage (13 a diameter) and would require two neighbour supercages. Therefore the synthesis of BTP adsorbed in the pore of zeolite Y is particularly challenging. The target of this work is to determine how the special structure of BTP is reflected in its photocatalytic activity compared to that of TP@Y.