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The Singlet–Triplet Exchange Energy in Conjugated Polymers
Author(s) -
Köhler A.,
Beljonne D.
Publication year - 2004
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200305032
Subject(s) - singlet state , conjugated system , materials science , singlet fission , exchange interaction , triplet state , excited state , polymer , quantum yield , molecule , chemical physics , photochemistry , molecular physics , atomic physics , condensed matter physics , chemistry , fluorescence , physics , organic chemistry , quantum mechanics , ferromagnetism , composite material
Electron–electron interactions in organic semiconductors split the lowest singlet and triplet states by the exchange energy, Δ E ST . Measurement of singlet and triplet emission spectra in a large number of conjugated polymers yield an almost constant Δ E ST value close to 0.7 eV. This is in contrast to the situation in molecules, where the exchange energy is found to depend on molecular size and to vary over a wide range. Quantum‐chemical calculations are performed to address the origin of the constant exchange energy in phenylene‐based conjugated polymers. The electron–hole separation in the lowest singlet and triplet excited states is found to be independent of the π‐conjugated backbone, and saturates for chains longer than a few repeating units, resulting in a constant exchange energy. In shorter conjugated oligomers, confinement of the excitations destabilizes the singlet with respect to the triplet through exchange interactions and leads to a larger and size‐dependent singlet–triplet energy separation.