Twisted intramolecular charge transfer of nitroaromatic push-pull chromophores

Sebok Lee; Myungsam Jen; Taehyung Jang; Gisang Lee; Yoonsoo Pang

doi:10.1038/s41598-022-10565-6

Twisted intramolecular charge transfer of nitroaromatic push-pull chromophores

Sci Rep. 2022 Apr 21;12(1):6557. doi: 10.1038/s41598-022-10565-6.

Authors

Sebok Lee¹, Myungsam Jen¹, Taehyung Jang¹, Gisang Lee¹, Yoonsoo Pang²

Affiliations

¹ Department of Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 61005, Republic of Korea.
² Department of Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 61005, Republic of Korea. ypang@gist.ac.kr.

Abstract

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 S₁ 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 S₁ 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.

Abstract

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