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

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., …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