Transient Raman Snapshots of the Twisted Intramolecular Charge Transfer State in a Stilbazolium Dye.
Shreetama KarmakarAbhinandan AmbasthaAjay JhaAditya DharmadhikariJayashree DharmadhikariRavindra VenkatramaniJyotishman DasguptaPublished in: The journal of physical chemistry letters (2020)
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.
Keyphrases
- raman spectroscopy
- energy transfer
- epithelial mesenchymal transition
- quantum dots
- molecular dynamics simulations
- living cells
- single molecule
- small molecule
- highly efficient
- density functional theory
- oxidative stress
- gene expression
- fluorescence imaging
- aqueous solution
- fluorescent probe
- photodynamic therapy
- signaling pathway
- blood brain barrier
- monte carlo