Excited-state symmetry breaking in quadrupolar pull-pushpull molecules: dicyanovinyl vs. cyanophenyl acceptors

Verma, Pragya, Tasior, Mariusz, Roy, Palas, Meech, Stephen R. ORCID: https://orcid.org/0000-0001-5561-2782, Gryko, Daniel T. and Vauthey, Eric (2023) Excited-state symmetry breaking in quadrupolar pull-pushpull molecules: dicyanovinyl vs. cyanophenyl acceptors. Physical Chemistry Chemical Physics, 25 (34). pp. 22689-22699. ISSN 1463-9076

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A significant number of quadrupolar dyes behave as their dipolar analogues when photoexcited in polar environments. This is due to the occurrence of excited-state symmetry breaking (ES-SB), upon which the electronic excitation, initially distributed over the whole molecule, localises preferentially on one side. Here, we investigate the ES-SB properties of two A–D–A dyes, consisting of a pyrrolo-pyrrole donor (D) and either cyanophenyl or dicyanovinyl acceptors (A). For this, we use time-resolved vibrational spectroscopy, comparing IR absorption and femtosecond stimulated Raman spectroscopies. Although dicyanovinyl is a stronger electron-withdrawing group, ES-SB is not observed with the dicyanovinyl-based dye even in highly polar media, whereas it already takes place in weakly polar solvents with dyes containing cyanophenyl accepting groups. This difference is attributed to the large electronic coupling between the D–A branches in the former dye, whose loss upon symmetry breaking cannot be counterbalanced by a gain in solvation energy. Comparison with analogues of the cyanophenyl-based dye containing different spacers reveals that interbranch coupling does not so much depend on the distance between the D–A subunits than on the nature of the spacer. We show that transient Raman spectra probe different modes of these centrosymmetric molecules but are consistent with the transient IR data. However, lifetime broadening of the Raman bands, probably due to the resonance enhancement, may limit the application of this technique for monitoring ES-SB.

Item Type: Article
Additional Information: Data availability: All data can be downloaded from https://doi.org/10.26037/yareta:nxbnwv5fkje7dfll5y5jicypd4. Electronic supplementary information (ESI) available: Solvatochromism, time resolved fluorescence, transient electronic and IR absorption spectra and results from global analysis, acquisition of the FSRS spectra, and results from quantum-chemical calculations. See DOI: https://doi.org/10.1039/d3cp02810k Funding information: This work was financially supported by the Swiss National Science Foundation (grant 200020-184607), the University of Geneva, the National Science Centre, Poland (OPUS 2020/37/B/ST4/00017), and EPSRC for grant EP/R042357/1.
Uncontrolled Keywords: physics and astronomy(all),physical and theoretical chemistry ,/dk/atira/pure/subjectarea/asjc/3100
Faculty \ School: Faculty of Science > School of Chemistry
UEA Research Groups: Faculty of Science > Research Groups > Centre for Photonics and Quantum Science
Faculty of Science > Research Groups > Chemistry of Light and Energy
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Depositing User: LivePure Connector
Date Deposited: 24 Aug 2023 12:31
Last Modified: 06 Sep 2023 08:30
URI: https://ueaeprints.uea.ac.uk/id/eprint/92923
DOI: 10.1039/D3CP02810K


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