Laser-induced linear and non-linear optical features in novel benzoxazole-based on donor-acceptor chromophores

Abstract

The photophysical properties of donor-acceptor based benzoxazoles were investigated by means of steady-state and time-resolved fluorescence techniques. Additionally, laser stimulated second-order optical effects (preliminary second harmonic generation (SHG) were studied. The studies show that the nitro-benzoxazole derivatives decorated with different alkylo/arylo amino groups dissolved in medium polar aprotic solvents: tetrahydrofuran and butyl chloride, exhibit dual fluorescence from the locally excited state (1LE) and a highly polar charge transfer (CT) state. Ambient-temperature time-resolved fluorescence investigations prove the bimodal kinetics of the excited-state electron transfer reaction 1LE→1CT. The lack of any CT emissions in cyclohexane and highly polar acetonitrile is presumably due to an efficient inter-system crossing process or fast deactivation of a low-lying CT state. In addition, strong CT properties inspired us to check a possibility to vary the absorption of the first UV–Vis maxima under influence of the external bicolour coherent laser light and the related optical second harmonic generation (SHG). The two coherent beams of the infrared Er:glass laser at 1540 nm/770 nm formed gratings in the photopolymer solidified chromophore. The performed experiments are compared with the theoretically calculated electronic parameters within the B3LYP DFT approach. The presented data open novel type of materials, allowing to operate its transparency using external IR laser light in the near IR spectral range.