Synthesis and Properties of Novel Borondipyrromethene (BODIPY)-Tethered Triphenylamine Conjugates

Abstract

A series of novel donor–acceptor type borondipyrromethene (BODIPY)-tethered triphenylamine conjugates (BDP4–8) containing one or two BODIPY cores attached to a triphenylamine scaffold at the 4- or 4,4′- positions were successfully synthesised via a mild and effective protocol. Their photophysical and electrochemical properties were investigated. The absorption spectra indicated that the meso-substituted BODIPY with triphenylamine did not give rise to an intense intramolecular charge transfer (ICT) and did not effectively extend the conjugated length compared with substitution at the 2,6- and 3,5-positions as previously reported. It is worth noticing that the asymmetric mono-BODIPY-tethered triphenylamine conjugates (BDP5, BDP7) showed an electronic distribution imbalance due to the special 3D propeller shape of triphenylamine resulting in twisted molecular space configurations. In contrast, the symmetric bis-BODIPY-tethered triphenylamine conjugates (BDP4, BDP6, and BDP8) exhibited a balanced electronic distribution. The photoluminescence spectra of these conjugates exhibited significant Stokes shifts (5300–6700 cm–1), which caused fluorescence emission spectra in near-infrared regions. Cyclic voltammograms reveal that the asymmetric mono-BODIPY-tethered triphenylamine conjugates (BDP5, BDP7) have higher LUMO energy levels and lower HOMO energy levels, thus resulting in larger bandgaps than the bis-BODIPY-tethered triphenylamine ones.