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Charge‐recombination processes in oligomer‐ and polymer‐based light‐emitting diodes: A molecular picture
Author(s) -
Beljonne David,
Shuai Zhigang,
Ye AiJun,
Brédas JeanLuc
Publication year - 2005
Publication title -
journal of the society for information display
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.578
H-Index - 52
eISSN - 1938-3657
pISSN - 1071-0922
DOI - 10.1889/1.1927734
Subject(s) - citation , computer science , physics , philosophy , art history , art , library science
— An overview of our recent work on the mechanisms of singlet and triplet exciton formation in electroluminescent π‐conjugated materials will be presented. According to simple spin statistics, only one‐fourth of the excitons are formed as singlets. However, deviations from that statistics can occur if the initially formed triplet charge‐transfer (CT) excited states are amenable to intersystem crossing or dissociation. Although the electronic couplings between the CT states and the neutral exciton states are expected to be largest for the lowest singlet and triplet excitons ( S 1 and T 1 , respectively), the possibility for direct recombination into T 1 is always very small due to the large exchange energy. In small molecules, spin statistics is expected to be observed because both singlet and triplet exciton formations proceed via higher‐lying S n / T n states with similar electronic couplings and fast formation rates. In extended conjugated chains, however, that the 1 CT → S 1 pathway is faster while the 3 CT → T n channels become much slower, opening the route to intersystem crossing or dissociation among the 3 CT states.