The effect of molecular structure on intramolecular charge-transfer in 1,3,4-oxadiazole derivatives

Abstract

In order to study the effect of molecular structure on intramolecular charge transfer character, we designed and synthesized three methoxyphenyl substituted 1,3,4-oxadiazole derivatives, where the D-A branches are attached to the core benzene ring in different ways. The photophysical properties of these three molecules were systematically investigated by means of experimental and theoretical studies. Different degrees of fluorescence red-shift in polar solvents were observed in these compounds. Both 1,4-substituted L-OXD and 1,3-substituted B-OXD exhibit a 30˜40 nm red-shift in the fluorescence spectra during the increase of solvent polarity, while 1,3,5-substituted T-OXD exhibits more obvious solvatochromic behavior (>100 nm) than L-OXD and B-OXD, points to a large increase in the dipole moment of the excited state of T-OXD with solvent polarity. Furthermore, theoretical analysis on the electron density map and ADCH charge indicated that the electron is transferred from side methoxyphenyl units to 1,3,4-oxadiazole ring and center benzene ring, and more transferred charge could be observed in T-OXD. These results reflect that constructing octupolar molecular structures could be an effective way to influence the ICT character.