Quenching of the excitation energy of coumarin dyes by aniline

Quenching mechanisms of coumarin dyes, namely 6-bromo-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin (6BDTC) and 8-methoxy-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin (8MDTC), were carried out in toluene by adopting two methods, namely steady-state and time-resolved methods, to understand the role of diffusion in the quenching mechanism. The solute molecules were excited by UV radiation of wavelength 360 and 330 nm. Various quenching parameters like frequency of encounter (k_d), probability of quenching per encounter (p and p), and quenching rate parameter (k_q and k_q) were experimentally determined in all the solvents. Activation energy of quenching (E_a and E_a) was also determined by using the literature values of activation energy of diffusion (E_d). It was found that the values of E_a (and E_a) were less than E_d indicating that the quenching reactions are more significantly influenced by diffusion.