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Mode specific excited state dynamics study of bis(phenylethynyl)benzene from ultrafast Raman loss spectroscopy

Roy, Khokan; Kayal, Surajit; Ariese, Freek; Beeby, Andrew; Umapathy, Siva

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Authors

Khokan Roy

Surajit Kayal

Freek Ariese

Siva Umapathy



Abstract

Femtosecond transient absorption (fs-TA) and Ultrafast Raman Loss Spectroscopy (URLS) have been applied to reveal the excited state dynamics of bis(phenylethynyl)benzene (BPEB), a model system for one-dimensional molecular wires that have numerous applications in opto-electronics. It is known from the literature that in the ground state BPEB has a low torsional barrier, resulting in a mixed population of rotamers in solution at room temperature. For the excited state this torsional barrier had been calculated to be much higher. Our femtosecond TA measurements show a multi-exponential behaviour, related to the complex structural dynamics in the excited electronic state. Time-resolved, excited state URLS studies in different solvents reveal mode-dependent kinetics and picosecond vibrational relaxation dynamics of high frequency vibrations. After excitation, a gradual increase in intensity is observed for all Raman bands, which reflects the structural reorganization of Franck-Condon excited, non-planar rotamers to a planar conformation. It is argued that this excited state planarization is also responsible for its high fluorescence quantum yield. The time dependent peak positions of high frequency vibrations provide additional information: a rapid, sub-picosecond decrease in peak frequency, followed by a slower increase, indicates the extent of conjugation during different phases of excited state relaxation. The CC triple (–C≡C–) bond responds somewhat faster to structural reorganization than the CC double (>C=C<) bonds. This study deepens our understanding of the excited state of BPEB and analogous linear pi-conjugated systems and may thus contribute to the advancement of polymeric “molecular wires.”

Citation

Roy, K., Kayal, S., Ariese, F., Beeby, A., & Umapathy, S. (2017). Mode specific excited state dynamics study of bis(phenylethynyl)benzene from ultrafast Raman loss spectroscopy. The Journal of Chemical Physics, 146(6), Article 064303. https://doi.org/10.1063/1.4975174

Journal Article Type Article
Acceptance Date Jan 18, 2017
Online Publication Date Feb 8, 2017
Publication Date Feb 8, 2017
Deposit Date Jul 17, 2017
Publicly Available Date Feb 8, 2018
Journal Journal of Chemical Physics
Print ISSN 0021-9606
Electronic ISSN 1089-7690
Publisher American Institute of Physics
Peer Reviewed Peer Reviewed
Volume 146
Issue 6
Article Number 064303
DOI https://doi.org/10.1063/1.4975174
Public URL https://durham-repository.worktribe.com/output/1354899

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