Probing the electronic structure and photophysics of thiophene–diketopyrrolopyrrole derivatives in solution

Daniel W Polak, Mariana Casal, Josene Toldo, Xiantao Hu, Giordano Amoruso, Olivia Pomeranc, Martin Heeney, Mario Barbatti, Michael N R Ashfold, Thomas A A Oliver

Research output: Contribution to journalArticle (Academic Journal)peer-review

4 Citations (Scopus)
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Abstract

Diketopyrrolopyrroles are a popular class of electron-withdrawing unit in optoelectronic materials. When combined with electron donating side-chain functional groups such as thiophenes, they form a very broad class of donor-acceptor molecules: thiophene- diketopyrrolopyrroles (TDPPs). Despite their widescale use in biosensors and photovoltaic materials, studies have yet to establish the important link between the electronic structure of the specific TDPP and the critical optical properties. To bridge this gap, ultrafast transient absorption with 22 fs time resolution has been used to explore the photophysics of three prototypical TDPP molecules: a monomer, dimer and polymer in solution. Interpretation of experimental data was assisted by a recent high-level theoretical study, and additional density functional theory calculations. These studies show that the photophysics of these molecular prototypes under visible photoexcitation are determined by just two excited electronic states, having very different electronic characters (one is optically bright, the other dark), their relative energetic ordering and the timescales for internal conversion from one to the other and/or to the ground state. The underlying difference in electronic structure alters the branching between these excited states and their associated dynamics. In turn, these factors dictate the fluorescence quantum yields, which are shown to vary by ~1–2 orders of magnitude across the TDPP prototypes investigated here. The fast non-radiative transfer of molecules from the bright to dark states is mediated by conical intersections. Remarkably, wavepacket signals in the measured transient absorption data carry signatures of the nuclear motions that enable mixing of the electronic-nuclear wavefunction and facilitate non-adiabatic coupling between the bright and dark states.
Original languageEnglish
Pages (from-to)20138–20151
Number of pages14
JournalPhysical Chemistry Chemical Physics
Volume24
Issue number34
DOIs
Publication statusPublished - 15 Aug 2022

Bibliographical note

Funding Information:
The authors at Bristol and Aix-Marseille acknowledge funding from the European Union's Horizon 2020 Research and Innovation programme, under grant agreement 828753 (Boostcrop). T. A. A. O. acknowledges financial support from the Royal Society for a University Research Fellowship (UF1402310 and URF\R\201007) and Research Fellows Enhancement Awards (RGF\EA\180076 and RF\ERE\210045). The authors at Aix-Marseille Université acknowledge the Centre de Calcul Intensif d'Aix-Marseille for granting access to its high-performance computing resources and the HPC/AI resources from GENCI-TGCC (Grant 2022 – A0110813035). M. H. thanks the Royal Society and the Wolfson Foundation for financial support.

Funding Information:
The authors at Bristol and Aix-Marseille acknowledge funding from the European Union's Horizon 2020 Research and Innovation programme, under grant agreement 828753 (Boostcrop). T. A. A. O. acknowledges financial support from the Royal Society for a University Research Fellowship (UF1402310 and URF\R\201007) and Research Fellows Enhancement Awards (RGF\EA\180076 and RF\ERE\210045). The authors at Aix-Marseille Université acknowledge the Centre de Calcul Intensif d'Aix-Marseille for granting access to its high-performance computing resources and the HPC/AI resources from GENCI-TGCC (Grant 2022 - A0110813035). M. H. thanks the Royal Society and the Wolfson Foundation for financial support.

Publisher Copyright:
© 2022 The Royal Society of Chemistry.

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