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# Neutral and Charged Excited States in Polar Organic Films: Origin of Unusual Electroluminescence in Tri-p-tolylamine-Based Hole Conductors

Mukhopadhyay, S and Topham, BJ and Soos, ZG and Ramasesha, S (2008) Neutral and Charged Excited States in Polar Organic Films: Origin of Unusual Electroluminescence in Tri-p-tolylamine-Based Hole Conductors. In: Journal of Physical Chemistry A, 112 (31). pp. 7271-7279.

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## Abstract

The photoluminescence (PL) and electroluminescence (EL) of thin films of 1,1-bis[(di-4-tolylamino)phenyl]- cyclohexane (TAPC) are remarkably different. Similar PL and EL are instead observed in films of the closely related donors tri-p-tolylamine (TTA) and $N,N^{\prime}$-diphenyl-$N,N^{\prime}$-bis(3-methylphenyl)-($1,1^{\prime}$-biphenyl)-$4,4^{\prime}$-diamine (TPD). Such films show a wide range of hole transport that depends on the morphology and on external parameters such as temperature and electric field. Restricted configuration-interaction calculations performed on TTA, TAPC, TPD, and radical ions of TTA indicate that the unusual EL of TAPC films is due to direct recombination from a low-lying charge-transfer (CT) state. The CT state is strongly stabilized by electrostatic interactions with the polar environment. Theory confirms that TAPC can be considered a dimer of TTA. The charge distributions of $TTA^+$ and $TTA^-$ indicate charge localization in the anion that rationalizes low electron mobility as well as a strong charge-induced-dipole stabilization of the CT state.

Item Type: Journal Article Copyright of this article belongs to American Chemical Society. Division of Chemical Sciences > Solid State & Structural Chemistry Unit 20 Oct 2008 05:02 19 Sep 2010 04:51 http://eprints.iisc.ernet.in/id/eprint/16154

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