Internal heavy atom effect on the radiative and non-radiative rate constants in xanthene dyes |
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Authors: | NB Joshi P Gangola DD Pant |
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Institution: | Department of Physics, D.S.B. College, Kumaun University, Naini Tal, India |
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Abstract: | Flourescence quantum yield (øf), phosphorescence and fluorescence quantum yield ratio (øp/øf) and the observed triplet decay time (τpo) of fluorescein and its halogen derivatives have been measured. On halogen substitution an increase in øp/øf and a decrease in øf and τpo is observed in the sequence of Cl, Br, and I. The increase in øp/øf is not in the same proportion as the decrease in τpo. Although øp/øf is higher for cations than for dianions, it increases more for dianions on halogen substitution. However, the increase in 1/τpo is about 103 times more for cations than for dianions. The radiative and non-radiative rate constants viz., kis, kp and kqp have been calculated. On halogen substitution kf remains almost constant, whereas an increase in kp, kis and kqp is observed. For dianions the increase occurs in the order kqp> kis> kp while for cations the order is kqp> kp> kis. The deuterium solvent effect on triplet decay time and intensity is also observed. |
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