On the Singlet-Triplet Splitting of Geminate Electron-Hole Pairs in Organic Semiconductors

[en] Because of their unique photophysical properties, organic semiconductors have shown great promise in both light-emitting devices (LEDs) and photovoltaic systems. In particular, the question of spin statistics looms large in these applications: the relative energetics and rates of formation for singlet versus triplet excited states can have a significant impact on device efficiency. In this Article, we study the singlet and triplet charge-transfer (CT) configurations that can be thought of as the immediate precursors to the luminescent states in organic LEDs. In particular, we find that the CT singlet-triplet energy gap (?EST) of organic dyes and oligomers depends sensitively on both the material and the relative orientation of the donor/acceptor pair. Furthermore, in contrast with the commonly held view, we find that the singlet CT states nearly always lie energetically below the triplet CT states (?EST < 0). This trend is attributed to two physical sources. First, the relatively close contact between the donor and acceptor leads to a strong kinetic exchange component that favors the singlet. Second, Coulombic attraction between the separated charges favors inner-sphere reorganization that brings the donor and acceptor closer together, further enhancing the kinetic exchange effect. We discuss the implications of these results on the design of organic LEDs.

Disciplines :

Physics

Author, co-author :

Difley, S.

Beljonne, David ; Université de Mons > Faculté de Médecine et de Pharmacie > Chimie générale, organique et biomédicale ; Université de Mons > Faculté des Sciences > Chimie des matériaux nouveaux

Van Voorhis, T.

Language :

English

Title :

On the Singlet-Triplet Splitting of Geminate Electron-Hole Pairs in Organic Semiconductors

Publication date :

19 March 2008

Journal title :

Journal of the American Chemical Society

ISSN :

0002-7863

Publisher :

American Chemical Society, United States - District of Columbia

Volume :

130

Issue :

Pages :

3420-3427

Peer reviewed :

Peer Reviewed verified by ORBi

Research unit :

S817 - Chimie des matériaux nouveaux

Research institute :

R400 - Institut de Recherche en Science et Ingénierie des Matériaux

Commentary :

Publié en ligne le 21 février 2008

Available on ORBi UMONS :

since 10 June 2010

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