Investigation of photophysical properties of new branched compounds with triazine and benzimidazole units

Abstract

Three new acceptor–donor–acceptor branched compounds with triazine and benzimidazole units (M1, M2, and M3) were synthesized and characterized by infrared, hydrogen-1 nuclear magnetic resonance, carbon-13 nuclear magnetic resonance, mass spectrometry, and elemental analysis. Their photophysical properties were investigated including linear absorption, single-photon excited fluorescence, fluorescence quantum yield, two-photon absorption, and frequency up-converted fluorescence. When the number of branches increases, the spectral positions of the linear absorption and the single-photon excited fluorescence show red shifts, while the fluorescence quantum yields decrease. When the polarity of solvents increases, the spectral positions of the single-photon excited fluorescence and the Stokes shifts also show red shifts, while the fluorescence quantum yields of the two-branched compound (M2) and three-branched compound (M3) decrease. Under the excitation of an 800 nm laser with a pulse width of 80 fs, all these compounds emit intense green frequency up-converted fluorescence, and the two-photon absorption cross-sections are 210, 968, and 1613 GM for M1, M2, and M3, respectively. This result shows that significant enhancement of the two-photon absorption cross-section can be achieved by sufficient electronic coupling between the strong charge transfer acceptor–donor–acceptor quadrupolar branches through the s-triazine core.