Photophysical properties of two selectively substituted bicoumarins bridged by a flexible single covalent bond have been investigated in solvents of varying polarity. The results show that the second coumarin moiety acts merely as a substituent to the parent coumarin which is still the main chromophore and has a minimal influence on the overall photophysical properties of the molecule. The solvent dependent spectral shifts are indicative of an intramolecular charge transfer nature of the lowest excited state of both the dyes. The sustenance of fluorescence of dye II where the there are no additional electron-withdrawing substituents attached to the aminocoumarin nucleus, while the quenching of fluorescence along with a decrease in lifetime of dye I, − which has an additional electron-withdrawing cyano group in the 4-position of the parent coumarin in highly polar solvents is explained in terms of the well-accepted ICT−TICT hypothesis.
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B. Bangar Raju (1997) studied this question.
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