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.sub.d]), probability of quenching per encounter (p and p=), and quenching rate parameter (kq and k'q) were experimentally determined in all the solvents. Activation energy of quenching ([E.sub.a] and [E.sub.a]) was also determined by using the literature values of activation energy of diffusion ([E.sub.d]). It was found that the values of [E.sub.a] (and [E.sub.a]) were less than [E.sub.d] indicating that the quenching reactions are more significantly influenced by diffusion. PACS Nos.: 33.50.D, 33.50.-j, 87.64.i, 31.70.Hq. A l'aide des methodes stationnaire et resolue dans le temps, afin de comprendre le role de la diffusion dans le mecanisme d'extinction (de luminescence), nous avons active dans le toluene les mecanismes d'extinction de colorants coumarine, nommement le 6-bromo-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarine (6BDTC) et 8-methoxy-3-[1-(4,5- dicarbomethoxy-1,2,3triazoloacetyl)]coumarine (8MDTC). Les molecules de solute ont ete excitees par radiation UV de longueur d'onde 360 et 330 nm. Nous avons determine experimentalement, dans tous les solvants, differents parametres de desactivation, comme la frequence de collision ([k.sub.d]), la probabilite de desactivation par collision (p et p=) et le parametre de taux de desactivation (kq et kq). Utilisant les valeurs de la litterature pour l'energie d'activation de la diffusion ([E.sub.d]), nous avons determine les energies d'activation de desactivation ([E.sub.a] et [E.sub.a]). Nous trouvons que [E.sub.a] (et [E'.sub.a)] sont plus petites que [E.sub.d], ce qui indique que les reactions de desactivation sont significativement plus affectees par la diffusion. [Traduit par la Redaction]
1. Introduction The mechanism of decreasing the fluorescence intensity of a given substance is known as fluorescence quenching. The different types of quenching mechanisms are dynamic quenching, static quenching, and [...]