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Updated: Feb 11, 2026

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional π-conjugate Systems
Published on: February 10, 2020
Femtosecond Time-Resolved Raman Spectroscopy Reveals Structural Evidence for meta Effect in Stilbenols
Syed M Bilal1, Surajit Kayal2, Krishnankutty S Sanju1
1School of Chemistry , Indian Institute of Science Education and Research Thiruvananthapuram , Vithura, Thiruvananthapuram 695551 , India.
Abstract:
The meta effect in substituted aromatics plays a crucial role in their excited-state photophysical properties. Meta-substituted hydroxyarenes such as naphthols, stilbenols, and chromophoric constituents of green fluorescent proteins show unusual photoacidity and enhanced fluorescence lifetime and quantum yield when compared to their para-derivatives. Variation in the excited state features of the meta-derivatives when compared to the para-derivatives in stilbenols has been attributed to the enhanced torsional barrier for interconversion between the planar and the twisted perpendicular forms. Herein, we employed femtosecond time-resolved Raman spectroscopy to provide the direct structural evidence for the enhanced torsional barrier in meta-stilbenol. The Raman band profiles of the olefinic C═C stretch related to the torsional motion are found to decay with time constants of ∼750 and ∼13 ps in meta-stilbenol and para-stilbenol respectively, unraveling the structural evidence for the observed enhanced photoacidity originating from enhanced rates of excited-state proton transfer. Further, time-resolved fluorescence measurements are performed to elucidate the relaxation pathways of the excited states of the stilbenols.
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