title: 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 S0-->S1 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.
authors.affiliation: Institut für Organische Chemie, Am Hubland, Julius-Maximilians-Universität Würzburg, 97074 Würzburg, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Stahl
authors.forename: Christoph
authors.initials: C
authors.lastname: Lambert
authors.forename: Conrad
authors.initials: C
authors.lastname: Kaiser
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Wortmann
authors.forename: Ruth
authors.initials: R
authors.lastname: Jakober