Premium
Charge‐Transfer Character in a Covalent Diketopyrrolopyrrole Dimer: Implications for Singlet Fission
Author(s) -
Mauck Catherine M.,
Bae Youn Jue,
Chen Michelle,
PowersRiggs Natalia,
Wu YiLin,
Wasielewski Michael R.
Publication year - 2018
Publication title -
chemphotochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.13
H-Index - 18
ISSN - 2367-0932
DOI - 10.1002/cptc.201700135
Subject(s) - chromophore , singlet fission , intramolecular force , photochemistry , intermolecular force , dimer , photoexcitation , covalent bond , ultrafast laser spectroscopy , acceptor , singlet state , intersystem crossing , chemical physics , chemistry , materials science , spectroscopy , triplet state , excited state , stereochemistry , molecule , atomic physics , organic chemistry , physics , quantum mechanics , condensed matter physics
Diketopyrrolopyrrole (DPP) is a strongly absorbing, photostable chromophore that can undergo singlet fission (SF), a photophysical process that promises to significantly enhance solar‐cell performance. In the solid state, DPP packs in a herringbone arrangement that maximizes intermolecular donor–acceptor interactions, suggesting that charge‐transfer (CT) states play a role in DPP SF. In order to characterize intermolecular DPP CT states in molecular assemblies, we have synthesized a covalent DPP dimer bridged by a xanthene linker, which places two thiophene‐substituted DPPs (TDPPs) in a cofacial arrangement that mimics chromophore π–π stacking in the thin film. After photoexcitation in polar solvents, symmetry‐breaking charge separation forms the fully charge separated TDPP +. –TDPP −. ion‐pair state. In nonpolar solvents, charge separation is incomplete leading to the TDPP δ+ –TDPP δ− CT state, which is in pseudoequilibrium with the relaxed S 1 S 0 state observed by transient absorption and emission spectroscopy. This study highlights the importance of intramolecular coupling as well as the importance of entropy to promoting SF in chromophore dimers for which SF is endo‐ or isoergic.