QM/MM study of the role of the solvent in the formation of the charge separated excited state in 9,9'-bianthryl

Ferdinand C Grozema; Marcel Swart; Robert W J Zijlstra; Jacob J Piet; Laurens D A Siebbeles; Piet Th van Duijnen

doi:10.1021/ja051729g

QM/MM study of the role of the solvent in the formation of the charge separated excited state in 9,9'-bianthryl

J Am Chem Soc. 2005 Aug 10;127(31):11019-28. doi: 10.1021/ja051729g.

Authors

Ferdinand C Grozema¹, Marcel Swart, Robert W J Zijlstra, Jacob J Piet, Laurens D A Siebbeles, Piet Th van Duijnen

Affiliation

¹ DelftChemTech, Section Opto-Electronic Materials, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands. grozema@tnw.tudelft.nl

PMID: 16076209
DOI: 10.1021/ja051729g

Abstract

In this paper the role of the solvent in the formation of the charge-separated excited state of 9,9'-bianthryl (BA) is examined by means of mixed molecular mechanical/quantum mechanical (QM/MM) calculations. It is shown that in weakly polar solvents a relaxed excited state is formed with an interunit angle that is significantly smaller than 90 degrees . This relaxed excited state has a considerable dipole moment even in weakly polar solvents; for benzene and dioxane dipole moments of ca. 6 D were calculated, which is close to experimental data. These dipoles are induced by the solvent in the highly polarizable relaxed excited state of BA, and the dipole relaxation time is governed by solvent reorganizations. In polar solvent the charge separation is driven to completion by the stronger dipoles in the solvent and a fully charged separated excited state is formed with an interunit angle of 90 degrees.