Photoinduced dynamics of a cyanine dye: parallel pathways of non-radiative deactivation involving multiple excited-state twisted transients |
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| Authors: | Srigokul Upadhyayula Vicente Nu?ez Eli M Espinoza Jillian M Larsen Duoduo Bao Dewen Shi Jenny T Mac Bahman Anvari Valentine I Vullev |
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| Institution: | a Department of Bioengineering , University of California , Riverside , CA 92521 , USA . Email: ;b Department of Biochemistry , University of California , Riverside , CA 92521 , USA ;c Department of Chemistry , University of California , Riverside , CA 92521 , USA ;d Materials Science and Engineering Program , University of California , Riverside , CA 92521 , USA |
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| Abstract: | Cyanine dyes are broadly used for fluorescence imaging and other photonic applications. 3,3′-Diethylthiacyanine (THIA) is a cyanine dye composed of two identical aromatic heterocyclic moieties linked with a single methine, –CH. The torsional degrees of freedom around the methine bonds provide routes for non-radiative decay, responsible for the inherently low fluorescence quantum yields. Using transient absorption spectroscopy, we determined that upon photoexcitation, the excited state relaxes along two parallel pathways producing three excited-state transients that undergo internal conversion to the ground state. The media viscosity impedes the molecular modes of ring rotation and preferentially affects one of the pathways of non-radiative decay, exerting a dominant effect on the emission properties of THIA. Concurrently, the polarity affects the energy of the transients involved in the decay pathways and further modulates the kinetics of non-radiative deactivation. |
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