Excited-state photodynamics of pyrene-containing boronated dyes

Three pyrene-containing boronated dyes have been examined in order to evaluate the effect of pyrene moiety localization on the photophysical properties. (3-Fluorophenyl)-1-pyreneborinic 8-oxyquinolinate was obtained by reacting 1-lithiopyrene with 3-fluorophenylboronic diethyl ester followed by complexation with 8-hydroxyquinoline. This compound consists of a pyrene unit (Py) directly bonded to a boron-quinolinate moiety (BQ). Two diarylborinic complexes (boranils) with salicylaldimine ligands (SA) bearing a pyrene moiety were obtained by reacting bis(2,6-difluorophenyl)borinic ethyl ester with salicylaldehyde and 1-aminopyrene or N1-(pyren-1-ylmethyl)benzene-1,4-diamine. The first compound consists of pyrene unit directly bonded to the boron-containing boranil moiety (BA), while the other consists of a pyrene unit connected to the BA moiety via a 1-amino-4-methyleneaminophenyl linker. The obtained compounds were characterized by 1H and 13C NMR spectroscopy and X-ray crystallography. UV–Vis fluorescence measurements showed the strong influence of solvent on the observed emission maximum (λmax) and quantum yield of emission. For (3-fluorophenyl)-1-pyreneborinic 8-oxyquinolinate the excited pyrene unit lead to dual fluorescence (from Py and BQ) which was modulated by solvent polarity. The possible formation of the open form of this complex via B–N bond breakage influences strongly the photoinduced processes which was supported by the fluorescence lifetimes measurements and quantum mechanical calculations. For two boranils the BA emission was observed upon excitation of pyrene regardless on solvent polarity. In the case of boranil complex containing 1-amino-4-methyleneaminophenyl linker a significant increase in quantum yield in the solid state was observed which may be attributed to aggregation-induced emission.