Steady-state absorption and fluorescence study: Dipole moments of coumarins

Abstract

The absorption and fluorescence spectra of 7-dimethylamino cyclopenta [c] coumarin (C138) and 4-methyl-piperidino [g] coumarin (C339) dyes were measured in neutral, aprotic and protic solvents. Solvatochromic shifts of absorption and fluorescence as a function of different solvent polarity parameters (bulk as well as microscopic) were analyzed for these dyes and the ground state dipole moment (<img src='/image/spc_char/micro.gif' border=0> _g) and the first excited singlet state dipole moment (<img src='/image/spc_char/micro.gif' border=0> _e) were estimated to be <img src='/image/spc_char/micro.gif' border=0> _g = 2.2 and 3.42 D and <img src='/image/spc_char/micro.gif' border=0> _e = 4.58 and 5.2 D, respectively, for C138 and C339. The dipole moment values of <img src='/image/spc_char/micro.gif' border=0> _g = 3.4 D and <img src='/image/spc_char/micro.gif' border=0> _g = 3.8 D were also obtained for C138 and C339 respectively from <i style="">ab- initio</i> calculations. The results are compared and discussed.