The Two-Photon Excitation Fluorescence (TPEF) Enhancement of Dipolar Organic Chromophores in Y Zeolites
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Two-Photon Absorption (TPA) is a non-linear optical (NLO) process that involves simultaneous absorption of two photons. Efficiency of two photon absorption by organic compounds is influenced by many different factors, including the nature of the surrounding environment (e.g. polarity). In the present work, the influence of the constricting and highly polar environment of zeolites on two-photon absorption of incorporated nitrobenzoxadiazole (NBD) derivatives is investigated. Six different analogues of NBD chromophores consisting of unsubstituted, N-alkylated and N,N-dialkylated amines were investigated. All showed strong single photon fluorescence (either conventional or laser induced), and easily detected femtosecond laser two-photon induced fluorescence, both in solution and in zeolites. The results show that the efficiency of two-photon induced fluorescence remained largely unaffected by solvent polarity for all of the NBD derivatives examined. However, the efficiency of two-photon induced fluorescence was substantially influenced by the zeolite environment, with some NBD derivatives showing almost a 10-fold increase.