Photoinduced charge transfer in push-pull pyrazoline-based chromophores - Relationship between molecular structure and photophysical, photovoltaic properties

Tomasz Uchacz; Anna M Maroń; Paweł Szlachcic; Andrzej Danel; Monika Pokladko-Kowar; Ewa Gondek; Przemysław Kolek; Szczepan Zapotoczny; Katarzyna M Stadnicka

doi:10.1016/j.saa.2023.122643

Photoinduced charge transfer in push-pull pyrazoline-based chromophores - Relationship between molecular structure and photophysical, photovoltaic properties

Spectrochim Acta A Mol Biomol Spectrosc. 2023 Aug 5:296:122643. doi: 10.1016/j.saa.2023.122643. Epub 2023 Mar 21.

Authors

Tomasz Uchacz¹, Anna M Maroń², Paweł Szlachcic³, Andrzej Danel⁴, Monika Pokladko-Kowar⁴, Ewa Gondek⁴, Przemysław Kolek⁵, Szczepan Zapotoczny⁶, Katarzyna M Stadnicka⁶

Affiliations

¹ Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, 30-387 Kraków, Poland. Electronic address: tomasz.uchacz@uj.edu.pl.
² Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
³ Department of Chemistry, Faculty of Food Technology, University of Agriculture in Krakow, Balicka 122, 31-149 Kraków, Poland.
⁴ Faculty of Material Engineering and Physics, Cracow University of Technology, Podchorążych 1, 30-084 Kraków, Poland.
⁵ Institute of Physics, University of Rzeszów, 1 Pigonia Street, PL-35-310 Rzeszów, Poland.
⁶ Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, 30-387 Kraków, Poland.

PMID: 37001263
DOI: 10.1016/j.saa.2023.122643

Abstract

The manuscript describes the effect of molecular structure on the photophysical and photovoltaic properties of the pyrazoline-based donor-branched-π-system-acceptor compounds decorated with two end groups: phenyl or thiophene. Although the absorption to the first singlet excited state is strongly allowed, the emission quantum yield is low in all studied solvents. This behaviour was explained by the existence of two non-radiative deactivation channels: the back electron transfer process, especially operated in polar solvents, and internal conversion realized as the rotation of flexible rotors (cyano, keto phenyl or thiophene). The feasibility of the photoinduced electron transfer process was corroborated by electrochemical, spectroelectrochemical measurements as well as DFT calculations. DFT calculations also support the existence of multiple conformations in the ground state, which differ from one another in terms of charge distribution and the values of ground state dipole moment. Finally, the mechanism of the singlet excited state deactivation of the studied compounds was determined by ultrafast pump-probe measurements. Our studies revealed that charge/electron transfer process may undergo over carbonyl bridge, included in branched π-system. Moreover, the thiophene decorated pyrazoline is characterized by a better photovoltaic power conversion efficiency, while the phenyl-ended pyrazoline can be applied as a viscosity sensor.

Keywords: DFT calculation; Photoinduced charge transfer; Photovoltaic cell; Pyrazoline; Ultrafast spectroscopy; Viscosity probe.