Cyclic azacyanines: experimental and computational studies on spectroscopic properties and unique reactivity.

The absorption and fluorescence properties of cyclic azacyanine (CAC) derivatives were examined in several solvents. The presence of electron donating or withdrawing groups on the CAC impacts spectroscopic properties. The general solvent relaxation displayed by azacyanine derivatives is in accordance with Lippert-Mataga's prediction but exception is noted in the case of protic solvent due to specific hydrogen bonding interactions. Fluorescence lifetime decay studies indicate a relaxation time in the nanosecond timescale with mono exponential decay. Donating substituents markedly increase the excited state lifetime, whereas withdrawing groups marginally decrease the excited state lifetime. Quantum chemical computations were used to explore the origins of the reactivity and spectroscopic properties of CACs; results are consistent with a model in which regioselectivity results from differences in mechanistic steps occurring after initial attack by hydroxide on the CAC.

Fluorescence modulation of 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione by silver nanoparticles and its possible analytical application.

The effects of silver nanoparticles on the photophysical properties of 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, popularly known as curcumin, have been investigated using optical absorption and fluorescence techniques. Although absorption spectroscopy suggests a ground-state complex formation, fluorescence quenching data confirms a simultaneous static and dynamic quenching, inferring ground as well as excited-state complex formation. The recovery of fluorescence quenching of the curcumin-silver nanoparticle complex in the presence of ascorbic acid or uric acid emphasizes a strong interaction between the silver nanoparticles and ascorbic acid/uric acid, suggesting that fluorescence recovery after the quenching of curcumin-silver nanoparticle complexes has potential for ascorbic acid or uric acid assay development.

Influence of substituent and solvent on the radiative process of singlet excited states of novel cyclic azacyanine derivatives.

The photophysical properties of novel cyclic azacyanine derivatives have been investigated in acetonitrile, N-butyronitrile, methanol, ethanol, DMF and water. Introduction of electron donating or accepting groups on the cyclic azacyanine has a direct impact on the spectroscopic and photophysical properties. Irrespective of the nature of the substitution, azacyanine shows a general solvent relaxation in accordance with Lippert-Mataga's prediction; however, in protic solvent, specific interactions are encountered. Fluorescence lifetime decay suggests a relaxation in the nanosecond time scale with monoexponential decay in polar solvents and biexponential decay in non polar solvents. The fluorescence lifetime of azacyanines are found to be longer than popular cy3 dyes. An electron donating substituent increases the fluorescence lifetime and influences the radiative process, whereas an electron withdrawing group marginally increases the excited state lifetime but remarkably enhances the radiative process. The fluorescence quantum yield of substituted cyclic azacyanine in water is noted to be at least five fold higher than the popular cy3 dye.