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Excited‐State Intramolecular Charge‐Transfer Dynamics in 4‐Dimethylamino‐4′‐cyanodiphenylacetylene: An Ultrafast Raman Loss Spectroscopic Perspective

Barak, Arvind; Dhiman, Nishant; Sturm, Floriane; Rauch, Florian; Lakshmanna, Yapamanu Adithya; Findlay, Karen S.; Beeby, Andrew; Marder, Todd B.; Umapathy, Siva

Excited‐State Intramolecular Charge‐Transfer Dynamics in 4‐Dimethylamino‐4′‐cyanodiphenylacetylene: An Ultrafast Raman Loss Spectroscopic Perspective Thumbnail


Authors

Arvind Barak

Nishant Dhiman

Floriane Sturm

Florian Rauch

Yapamanu Adithya Lakshmanna

Karen S. Findlay

Todd B. Marder

Siva Umapathy



Abstract

The D-π-A compound 4-dimethylamino-4′-cyanodiphenylacetylene (DACN-DPA) exhibits intramolecular charge transfer (ICT) upon photoexcitation. Ultrafast Raman Loss Spectroscopy (URLS) measurements show distinct spectral and temporal dynamics of C≡C and C=C vibrational modes in MeCN and n-hexane, revealing that ICT is strongly coupled to the structural dynamics. Photo-initiated intramolecular charge transfer (ICT) processes play a pivotal role in the excited state reaction dynamics in donor-bridge-acceptor systems. The efficacy of such a process can be improved by modifying the extent of π-conjugation, relative orientation/twists of the donor/acceptor entities and polarity of the environment. Herein, 4-dimethylamino-4′-cyanodiphenylacetylene (DACN-DPA), a typical donor-π-bridge-acceptor system, was chosen to unravel the role of various internal coordinates that govern the extent of photo-initiated ICT dynamics. Transient absorption (TA) spectra of DACN-DPA in n-hexane exhibit a lifetime of >2 ns indicating the formation of a triplet state while, in acetonitrile, a short time-constant of ∼2 ps indicates the formation of charge transferred species. Ultrafast Raman loss spectroscopy (URLS) measurements show distinct temporal and spectral dynamics of Raman bands associated with C≡C and C=C stretching vibrations. The appearance of a new band at ∼1492 cm−1 in acetonitrile clearly indicates structural modification during the ultrafast ICT process. Furthermore, these observations are supported by TD-DFT computations.

Citation

Barak, A., Dhiman, N., Sturm, F., Rauch, F., Lakshmanna, Y. A., Findlay, K. S., Beeby, A., Marder, T. B., & Umapathy, S. (2022). Excited‐State Intramolecular Charge‐Transfer Dynamics in 4‐Dimethylamino‐4′‐cyanodiphenylacetylene: An Ultrafast Raman Loss Spectroscopic Perspective. ChemPhotoChem, 6(12), Article e202200146. https://doi.org/10.1002/cptc.202200146

Journal Article Type Article
Acceptance Date Sep 2, 2022
Online Publication Date Sep 29, 2022
Publication Date 2022-12
Deposit Date Oct 25, 2022
Publicly Available Date Mar 22, 2023
Journal ChemPhotoChem
Print ISSN 2367-0932
Electronic ISSN 2367-0932
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 6
Issue 12
Article Number e202200146
DOI https://doi.org/10.1002/cptc.202200146
Public URL https://durham-repository.worktribe.com/output/1187528

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Publisher Licence URL
http://creativecommons.org/licenses/by/4.0/

Copyright Statement
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.






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