Electrochemistry and photophysics of donor-substituted triarylboranes: symmetry breaking in ground and excited state |
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Authors: | Stahl Rainer Lambert Christoph Kaiser Conrad Wortmann Rüdiger Jakober Ruth |
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Affiliation: | Institut für Organische Chemie, Am Hubland, Julius-Maximilians-Universit?t Würzburg, 97074 Würzburg, Germany. |
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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. |
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Keywords: | boranes charge transfer fluorescence spectroscopy solvatochromism symmetry breaking UV/Vis spectroscopy |
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