Photophysical studies on the interaction of PET and non-PET based acridinedionedyes with glycine in water

Abstract

Photophysical studies of resorcinol based acridinedione (ADDR) dyes with a simple amino acid like glycine were carried out in water. These ADDR dyes are classified into photoinduced electron transfer (PET) and non-PET based on the substitution on the acridinedione ring structure (Scheme 1). Addition of glycine to PET based dye containing a -OCH3 (ADDR1) moiety resulted in a fluorescence enhancement while to that of another PET dye containing (N (CH3)2) moiety (ADDR 4) exhibits a fluorescence quenching behaviour. Interestingly, addition of glycine to ADDR 1 dye not only results in a fluorescence enhancement but a significant shift in the emission maximum towards the red region resulted. On the contrary, no significant shift in the emission maximum neither towards blue nor red region results in the presence of ADDR4 dye. The fluorescence enhancement is attributed to the suppression of the PET process through space between the donor and the acceptor moiety of acridinedione dye ring structure. The fluorescence quenching of ADDR4 dye is attributed to change in the excited state properties of N, N-dimethyl moiety such that the local excited state (LE) nature is drastically quenched on the addition of glycine molecules. The fluorescence decay of all ADDR dyes exhibit single exponential decay in water whereas ADDR1 and ADDR4 dyes exhibit a bi-exponential decay in the presence of glycine. Addition of glycine to non-PET based ADDR dyes (ADDR2 and ADDR3) results no significant change in fluorescence emission intensity and fluorescence lifetime. The introduction of glycine implies that there exists two different microenvironment in the aqueous phase around the close vicinity of the ADDR dyes. A large variation in the fluorescence lifetime and their relative distribution of the dye located in different domains are elucidated by time resolved fluorescence spectral techniques. Both hydrogen-bonding along with hydrophobic interactions influences the excited state properties of PET based ADDR dyes in the presence of glycine are elucidated by fluorescence spectral techniques is presented in our study.