Twisted intramolecular charge transfer of nitroaromatic push–pull chromophores

• Published in: Scientific reports Vol. 12; no. 1; pp. 6557 - 11
• Main Authors: Lee, Sebok, Jen, Myungsam, Jang, Taehyung, Lee, Gisang, Pang, Yoonsoo
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 21.04.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 639/638/440; 639/638/440/949; Chromophores; Humanities and Social Sciences; multidisciplinary; Raman spectroscopy; Science; Science (multidisciplinary); Spectroscopy; Spectrum analysis
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-022-10565-6

The structural changes during the intramolecular charge transfer (ICT) of nitroaromatic chromophores, 4-dimethylamino-4′-nitrobiphenyl (DNBP) and 4-dimethylamino-4′-nitrostilbene (DNS) were investigated by femtosecond stimulated Raman spectroscopy (FSRS) with both high spectral and temporal resolutions. The kinetically resolved Raman spectra of DNBP and DNS in the locally-excited and charge-transferred states of the S 1 state appear distinct, especially in the skeletal vibrational modes of biphenyl and stilbene including ν 8a and ν C=C . The ν 8a of two phenyls and the ν C=C of the central ethylene group (only for stilbene), which are strongly coupled in the planar geometries, are broken with the twist of nitrophenyl group with the ICT. Time-resolved vibrational spectroscopy measurements and the time-dependent density functional theory simulations support the ultrafast ICT dynamics of 220–480 fs with the twist of nitrophenyl group occurring in the S 1 state of the nitroaromatic chromophores. While the ICT of DNBP occurs via a barrier-less pathway, the ICT coordinates of DNS are strongly coupled to several low-frequency out-of-phase deformation modes relevant to the twist of the nitrophenyl group.