Effect of quencher and temperature on fluorescence intensity of laser dyes: DETC and C504T

Fluorescence quenching of 7- Diethylamino-3-thenoylcoumarin (DETC) and 2,3,6,7-tetrahydro-1,1,7,7-tetramethyl11-oxo-1H,5H,11H- [1]benzopyrano[6,7,8-ij]quinolizine-10-carboxylic acid, ethyl ester (C504T) by aniline(AN), dimethylaniline (DMA) and diethylaniline (DEA) was investigated in toluene by steady state and transient methods. The quenching parameters like frequency of encounter (k(d)), probability of quenching per encounter (p), quenching rate parameters (k(q)) and activation energy of quenching (E-a) were determined experimentally. The k(q) values determined by steady state and time-resolved methods for the both dyes were found to be same, indicating the dynamic nature of interaction. Magnitudes of p and E-a suggested that the quenching reaction is predominantly controlled by material diffusion. The quenching mechanism is rationalized in terms of electron transfer (ET) from donors (aromatic amines) to the acceptors (coumarin derivatives) confirmed by correlating k(q) with free energy changes (Delta G degrees). Further, an effect of temperature on fluorescence intensity was carried out in toluene and methanol solvents. Fluorescence intensity of both the dyes decreases with increase in temperature. Temperature quenching in case of C504T is due to intersystem crossing S-1 -> T-2, whereas for DETC, quenching is due to intersystem crossing S-1 -> T-2 and ICT -> TICT transition. (C) 2016 Elsevier B.V. All rights reserved.