Nitro End Groups Remarkable Vibrational Reporters for Charge Transfer in the Excited States of Oligo(p-phenyleneethynylene)-Bridged Donor-Acceptor Dyads

J. Kubicki (1) , Maciej Lorenc (2) , P. Cochelin (2) , O. Mongin (3) , A. Amar (4) , A. Boucekkine (3) , A. Gaje (2) , M.G. Humphrey (5) , M. Morshedi (5) , S. Lorenzen (6) , F. Rauch (6) , C. Scheufler (6) , T.B. Marder (6) , Frédéric Paul (3)

1 UAM - Adam Mickiewicz University in Poznań
2 IPR - Institut de Physique de Rennes
3 ISCR - Institut des Sciences Chimiques de Rennes
4 USTHB - Université des Sciences et de la Technologie Houari Boumediene = University of Sciences and Technology Houari Boumediene [Alger]
5 ANU - Australian National University
6 JMU - Julius-Maximilians-Universität Würzburg

The D-π-A dyads [(n-Hex)2N(1,4-C6H4)]CC[(1,4-C6H4)NO2] (1) and [(n-Hex)2N(1,4-C6H4)]CC(1,4-C6H4)CC[(1,4-C6H4)NO2] (2) have been studied by ultrafast time-resolved infrared absorption spectroscopy. After excitation into their singlet charge-transfer (1CT) state, a fast decay (ca. 6 ps for 1 and 1 ps for 2) of the initially populated singlet state into a ground state (major pathway) and a longer lived excited state (possibly the triplet state) is observed. The nitro and alkyne groups were used as vibrational reporters to probe the changes induced by the charge-transfer process. For the first time, we confirm experimentally that these changes are consistent with expectations based on the traditional valence-bond representations of the CT states of these push-pull chromophores. An almost identical charge transfer takes place in the two dyads, despite π-bridges of different lengths between the donor and acceptor groups. Complementary DFT calculations support the experimental assignments and have helped clarify the photophysical behavior of 1 and 2.

Keywords: Absorption spectroscopy; Charge transfer; Chromophores; Ground state; Light absorption; Nitrogen oxides; Charge transfer process; DFT calculation; Donor and acceptor; Donor-acceptor dyads; Phenyleneethynylene; Photophysical behavior; Push-pull chromophores; Time-resolved infrared absorption spectroscopy; Excited states

Domains: Physics [physics]; Chemical Sciences

J. Kubicki, Maciej Lorenc, P. Cochelin, O. Mongin, A. Amar, et al.. Nitro End Groups Remarkable Vibrational Reporters for Charge Transfer in the Excited States of Oligo(p-phenyleneethynylene)-Bridged Donor-Acceptor Dyads. Journal of Physical Chemistry C, 2020, 124 (18), pp.9755-9764. ⟨10.1021/acs.jpcc.0c01532⟩. ⟨hal-02862821⟩