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Solvent‐Dependent Singlet Fission in Diketopyrrolopyrrole Dimers: A Mediating Charge Transfer versus a Trapping Symmetry‐Breaking Charge Separation
Author(s) -
Papadopoulos Ilias,
ÁlvaroMartins Maria João,
Molina Desiré,
McCosker Patrick M.,
Keller Paul A.,
Clark Timothy,
SastreSantos Ángela,
Guldi Dirk M.
Publication year - 2020
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.202001496
Subject(s) - singlet fission , singlet state , charge (physics) , excited state , intramolecular force , symmetry breaking , materials science , population , quantum yield , chemical physics , trapping , solvent , molecular physics , photochemistry , atomic physics , chemistry , fluorescence , physics , stereochemistry , organic chemistry , ecology , biology , demography , quantum mechanics , sociology
Three diketopyrrolopyrrole (DPP) dimers, linked via different dithienylphenylene spacers, ortho ‐DPP ( o ‐DPP), meta ‐DPP ( m ‐DPP), and para ‐DPP ( p ‐DPP), are synthesized, characterized, and probed in light of intramolecular singlet fission ( i ‐SF). Importantly, the corresponding DPP reference (DPP‐Ref) singlet and triplet excited state energies of 2.22 and 1.04 eV, respectively, suggest that i ‐SF is thermodynamically feasible. The investigations focus on the impact of the relative positioning of the DPPs, and give compelling evidence that solvent polarity and/or spatial overlap govern i ‐SF dynamics and efficiencies. Polar solvents make the involvement of an intermediate charge transfer (CT) state possible, followed by the population of 1 (T 1 T 1 ) and subsequently (T 1 + T 1 ), while spatial overlap drives the mutual interactions between the DPPs. In o ‐DPP, the correct balance between polar solvents and spatial overlap leads to the highest triplet quantum yield (TQY) of 40%. Notable is the superimposition of CT and triplet excited states, preventing an accurate TQY determination. For m ‐DPP, poorer spatial overlap correlates with weaker CT character and manifests in a TQY of 11%. Strong CT character acts as a trap and prevents i ‐SF, as found with p ‐DPP. The DPP separation is decisive, enabling a symmetry‐breaking charge‐separated state rather than CT formation, shutting down the formation 1 (T 1 T 1 ).