Effect of Solvents and Substituents on the Fluorescence Behaviour of Coumarin Dye Lasers
Rajesh Giri
Department of Physics and Electronics
Rajdhani College, University of Delhi, New Delhi, India.
In order to investigate the effect of solvents and substituents on the fluorescence behaviour of coumarin derivatives the absorption and fluorescence emission spectra of 4–phenyl substituted coumarins namely: 4-phenyl-7-hydroxy coumarin (1), 4-phenyl-7-methoxy coumarin (2), 4-phenyl-6-hydroxy-7-methoxy coumarin (3), 4-pheny-6,7-dimethoxy coumarin (4) and 4-phenyl-6,7-dihydroxy coumarin (5) have been studied in various organic solvents of varying dipole moment. It was found that in a given solvent the position of the absorption and fluorescence maxima depends on the nature and position of the additional substituent group linked to the 4-phenyl coumarin and the wavelengths shifts obtained are interpreted in terms of the changes in the mobility of π electrons. From the fluorescence emission spectra of the present coumarins it was found that the 4-phenyl coumarins are less fluorescent and show a smaller change in polarity on excitation as compared to the corresponding 3- henyl derivatives. These changes are interpreted in terms of the possible resonance structures of the coumarin derivatives.
Keywords: Fluorescence, Dipole moment, Resonance structures.
