Role of dipole moment of solvents in formation and stabilization of the TICT states in Coumarin 445 under nitrogen laser excitation

In this paper we report the observation of dual Amplified Spontaneous Emiss ion (ASE) from solutions of 7-ethylamino-4-methyl coumarin dye (Coumarin 44 5) in certain solvents such as n-butyl acetate, dioxane etc. when pumped by high power nitrogen laser. The two ASE bands appear to be from two differe nt excited species (ICT and TICT conformation) one of which is the precurso r of the other. The spectral characteristics of dye Coumarin 445 depend upo n the solvent environment. The TICT coumarin photoisomers, which form excip lexes with the solvent molecules, have enough gain to produce amplified spo ntaneous emission even when there is apparently no detectable fluorescence. The behaviour of this dye in the excited state is studied by measuring the small signal gain and variation of the gain slope with temperature in diff erent solvents. It is observed that polarity of the solvent plays a more do minant role in formation and stabilization of TICT states. (C) 2001 Elsevie r Science B.V. All rights reserved.