Mono- and bis-phenoxy-substituted 3-(quinolin-2-ylmethylene)isoindolin-1-ones and their boron complexes. Synthesis, photophysical properties and conductivity of thin films

Abstract

Heating 4-phenoxyphthalimide or 4,5-diphenoxyphthalimide with quinaldine in the presence of zinc oxide leads to the formation of (E,Z)-5(6)-phenoxy-3-(quinolin-2-ylmethylene)isoindolin-1-one and (E,Z)-5,6-diphenoxy-3-(quinolin-2-ylmethylene)isoindolin-1-one. By reacting them with BF3‧Et2O in the presence of Et3N in toluene, unsymmetrical analogs of BODIPY were synthesized, namely (Z)-2-(difluoroboryl)-5(6)-phenoxy-3-(quinolin-2-ylmethylene)isoindolin-1-one and (Z)-2-difluoroboryl-5,6-diphenoxy-3-(quinolin-2-ylmethylene)isoindolin-1-one, respectively. By structure of the synthesized compounds was confirmed by the data of elemental analysis, mass spectrometry, vibrational and NMR spectroscopy. The ligands have low fluorescence quantum yields (up to 0.14 relative to the standard) and significant Stokes shifts (up to 140 nm). In contrast, the complexes demonstrate high quantum yields (up to 0.44) and small Stokes shifts (7–8 nm). The fluorescence lifetimes of the complexes are close to 3 ns. To support the experimental data, DFT and TD-DFT calculations were carried out. Thin films of the complexes have a specific conductivity of 10−8 ÷ 10−9 S × cm−1 and the monophenoxy-substituted complex exhibits high photosensitivity.