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Download fileMultistage Complexation of Fluoride Ions by a Fluorescent Triphenylamine Bearing Three Dimesitylboryl Groups: Controlling Intramolecular Charge Transfer
journal contribution
posted on 2011-11-04, 00:00 authored by Hauke
C. Schmidt, Luisa G. Reuter, Josef Hamacek, Oliver S. WengerA propeller-shaped boron–nitrogen compound (NB3) with three binding sites for fluoride anions was synthesized
and
investigated by optical absorption, luminescence, and (1H, 11B, 13C, 19F) NMR spectroscopy.
Binding of fluoride in dichloromethane solution occurs in three clearly
identifiable steps and leads to stepwise blocking of the three initially
present nitrogen-to-boron charge transfer pathways. As a consequence,
the initially bright blue charge transfer emission is red-shifted
and decreases in intensity, until it is quenched completely in presence
of large fluoride excess. Fluoride binding constants were determined
from global fits to optical absorption and luminescence titration
data and were found to be Ka1 = 4 ×
107 M–1, Ka2 = 2.5 × 106 M–1, and Ka3 = 3.2 × 104 M–1 in
room temperature dichloromethane solution. Complexation of fluoride
to a given dimesitylboryl site increases the electron density at the
central nitrogen atom of NB3, and this leads to red shifts
of the remaining nitrogen-to-boron charge transfer transitions involving
yet unfluorinated dimesitylboryl groups.
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Keywords
absorptionelectron densityunfluorinated dimesitylboryl groups13 CFluorescent Triphenylamine Bearingcharge transfer emissionbinding sitesMultistage Complexationdimesitylboryl site increases19 FNBluminescence titration datanitrogen atom11 Bfluoride anionsdichloromethane solutionKa 1Ka 3Fluoride binding constantsFluoride IonsNMR spectroscopyDimesitylboryl Groupsroom temperature dichloromethane solution