Electrochemistry and Photophysics of Donor‐Substituted Triarylboranes: Symmetry Breaking in Ground and Excited State

Abstract

We synthesized a series of amino substituted triarylboranes (TABs) 1–3 by copper(I)‐catalyzed cross‐coupling reactions. The title compounds were investigated by means of cyclic voltammetry (CV) and UV‐visible absorption and fluorescence spectroscopy. Electrochemical oxidation of tris(4‐carbazolyl‐2,6‐dimethylphenyl)borane (3) leads to the formation of an electroactive polymer film on the electrode surface. The charge‐transfer (CT) absorption band of all three TABs shows a pronounced negative solvatochromism, while the emission is positively solvatochromic. By combining Jortner's theory, AM1 computations, and electrooptical absorption measurements (EOAM), this unexpected behavior was shown to be due to a dipole inversion upon S 0→S 1 excitation. Furthermore, polarized steady‐state fluorescence spectroscopy and EOAM prove that the ground‐state geometry of 3 is of lower symmetry than D3 and that the excitation energy can be transferred from one subchromophore to another within the lifetime of the excited state. Exciton‐coupling theory was used to quantitatively analyze this excitation transfer.