Multistage Complexation of Fluoride Ions by a Fluorescent Triphenylamine Bearing Three Dimesitylboryl Groups: Controlling Intramolecular Charge Transfer

Abstract

A propeller-shaped boron-nitrogen compound (NB(3)) with three binding sites for fluoride anions was synthesized and investigated by optical absorption, luminescence, and ((1)H, (11)B, (13)C, (19)F) 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 K(a1) = 4 × 10(7) M(-1), K(a2) = 2.5 × 10(6) M(-1), and K(a3) = 3.2 × 10(4) 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 NB(3), and this leads to red shifts of the remaining nitrogen-to-boron charge transfer transitions involving yet unfluorinated dimesitylboryl groups.

Charge‐Transfer Interactions in Tris‐Donor–Tris‐Acceptor Hexaarylbenzene Redox Chromophores

“…However, these findings disagree with the negative binding cooperativity that is found in many systems with more than one boron center 16b. e A reason for this disagreement could be the poor electronic coupling of the neighboring redox centers in HAB 2 . This hypothesis is also supported by the good agreement between the complexation constants of HAB 2 and that of model compound 3 .…”

Borylated Arylisoquinolines: Photophysical Properties and Switching Behavior of Promising Tunable Fluorophores

“…Fluorophores that contain trisubstituted boron species, such as triarylboranes or aryl boronic acids and their derivatives, have been intensively exploited for applications as luminescent polymeric materials,1–6 in nonlinear optics,7, 8 as model chromophores for the study of electron transfer,9, 10 and as chemosensors 11–14. The electron‐deficient nature of a trisubstituted boron atom in chromophoric architectures provides possibilities for the coordination of donor ligands through interactions with its vacant p π orbital.…”

Issue Information

“…This D–π–A approach has proven successful for the development of nonlinear optical materials, ambipolar charge carriers in organic light emitting devices (OLEDs), and fluorescent anion sensors 7. 8…”