Abstract
The spectral characteristics of trans-2-[4′-(N, N-dimethylamino)styryl]imidazo[4,5- b]pyridine (t-DMASIP-b) have been investigated using absorption and fluorescence techniques, and compared with 2-(4′- N, N-dimethylamino)imidazo[4,5- b]pyridine (DMAPIP-b). The study reveals that introduction of a C=C double bond strongly perturbs the photophysics of the system. Unlike DMAPIP-b, t-DMASIP-b emits a single emission in aprotic and protic solvents. The emission occurs from the locally excited state in nonpolar solvents and from a planar intramolecular charge transfer (PICT) state in polar solvents. Multiple linear regression analysis suggests that among the different solvent parameters, the dipolar interaction contributes more to the stabilization of the system in both the ground and excited states. Theoretical calculations suggest that, unlike in DMAPIP-b, proton coupled twisted intramolecular charge transfer (TICT) emission does not occur in t-DMASIP-b. The higher quantum yield obtained in the viscous solvent glycerol is attributed to the restriction of the twisting of the olefinic bond. The photoirradiation of t-DMASIP-b shows that isomerization takes place in all solvents, including viscous glycerol. The theoretically simulated potential energy surface shows that isomerization occurs via a phantom state, which is a nonradiative process. The rise in temperature favors the photoisomerization, thus, the fluorescence quantum yield decreases. The prototropic study indicates that, unlike in DMAPIP-b, the protonation takes place at different places to form the monocations.
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† Electronic supplementary information (ESI) available: Details of materials and methods, absorption spectra in different solvents, Lippert-Mataga equation, plot of temperature dependence of fluorescence quantum yield and emission spectra at different pHs. See DOI: 10.1039/c4pp00237g
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Mishra, A., Sahu, S., Tripathi, S. et al. Photoinduced intramolecular charge transfer in trans-2-[4′-(N, N-dimethylamino)styryl]imidazo[4,5- b]pyridine: effect of introducing a C=C double bond. Photochem Photobiol Sci 13, 1476–1486 (2014). https://doi.org/10.1039/c4pp00237g
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DOI: https://doi.org/10.1039/c4pp00237g