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Journal Article

Transient Raman Snapshots of the Twisted Intramolecular Charge Transfer State in a Stilbazolium Dye


Jha,  A.
Department of Chemical Sciences, TataInstitute of Fundamental Research;
Miller Group, Atomically Resolved Dynamics Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;

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Karmakar, S., Ambastha, A., Jha, A., Dharmadhikari, A., Dharmadhikari, J., Venkatramani, R., et al. (2020). Transient Raman Snapshots of the Twisted Intramolecular Charge Transfer State in a Stilbazolium Dye. The Journal of Physical Chemistry Letters, 11(12), 4842-4848. doi:10.1021/acs.jpclett.0c01124.

Cite as: http://hdl.handle.net/21.11116/0000-0006-C6BC-7
Optically triggered twisted intramolecular charge transfer (TICT) states in donor–acceptor chromophores form the molecular basis for designing bioimaging probes that sense polarity, microviscosity, and pH in vivo. However, a lack of predictive understanding of the “twist” localization precludes a rational design of TICT-based dyes. Here, using femtosecond stimulated Raman spectroscopy, we reveal a distinct Raman signature of the TICT state for a stilbazolium-class mitochondrial staining dye. Resonance-selective probing of 4-N,N-diethylamino-4″-N′-methyl-stilbazolium tosylate (DEST) tracks the excited-state structure of the dye as it relaxes to a TICT state on a picosecond time scale. The appearance of a remarkably blue-shifted C=C stretching mode at 1650 cm–1 in the TICT state is attributed to the “twist” of a single bond adjacent to the ethylenic π-bridge in the DEST backbone based on detailed electronic structure calculations and vibrational mode analysis. Our work demonstrates that the π-bridge, connecting the donor and acceptor moieties, influences the spatial location of the “twist” and offers a new perspective for designing organelle-specific probes through cogent tuning of backbone dynamics.