SSCU Student Seminar
Name: Mr. Sayan Ghosh
Title: Structural identification of the perpendicular intermediate of cis-trans photoisomerization
Date & Time: Thursday, 01st October 2026 at 4.00 p.m.
Venue: Rajarshi Bhattacharyya Memorial Lecture Hall, Chemical Sciences Building
Abstract:
Photoisomerization, a light-driven geometrical rotation around a double bond, serves as primary mechanism for vision[1], molecular photo switch[2], and various other applications. Stilbene molecule became one of the textbook models to understand this photochemistry. It was theorized in 1967 by Saltiel and coworkers[3] that the photoisomerization process proceeds via a common perpendicular intermediate state. But this intermediate state is so short-lived that nobody has actually probed its structure and dynamics. Because it was invisible to the experiment, it is often called the ‘Phantom State’.
In this seminar, I will present a recent work[4] on identifying the structure of this intermediate perpendicular state using femtosecond stimulated Raman spectroscopy (FSRS)[5] . This experiment reveals that the short-lived intermediate state exhibits a vibrational signature consistent with the perpendicular configuration, completing a 30-year-old experimental journey to finally have the structural evidence for the 60-year-old theoretical model.
References:
[1] D. Polli et al., ‘Conical intersection dynamics of the primary photoisomerization event in vision’, Nature, vol. 467, no. 7314, pp. 440–443, Sep. 2010.
[2] H. M. D. Bandara and S. C. Burdette, ‘Photoisomerization in different classes of azobenzene’, Chem. Soc. Rev., vol. 41, no. 5, pp. 1809–1825, Feb. 2012.
[3] J. Saltiel, ‘Perdeuteriostilbene. The Role of Phantom States in the cis-trans Photoisomerization of Stilbenes’, J. Am. Chem. Soc., vol. 89, no. 4, pp. 1036–1037, Feb. 1967.
[4] H. Kuramochi et al., ‘Ultrafast Raman observation of the perpendicular intermediate phantom state of stilbene photoisomerization’, Nature Chemistry, vol. 16, no. 1, pp. 22–27, Jan. 2024.
[5] P. Kukura, D. W. McCamant, and R. A. Mathies, ‘Femtosecond stimulated Raman spectroscopy’, Annu. Rev. Phys. Chem., vol. 58, no. Volume 58, 2007, pp. 461–488, May 2007.