Synthesis and Properties of Alkoxy-Bridged Triphenylene and Perylene Monoimide Diesters Dyads

Abstract

Columnar discotic liquid crystals have high charge carrier mobility, and donor-bridge-accepter-based supra-molecular compounds have photoinduced intramolecular electron transfer behavior. In order to make the organic materials possess these two performances, dyads composed of hexaalkoxy triphenylene unit and perylene monoimide diesters unit were prepared in this work. In the dyads, the flexible alkoxys were used as bridges, the triphenylene units having six electron-donating alkoxy tails acted as electron donors, and the perylene monoimide diesters units having four electron-withdrawing carbonyls acted as electron acceptors. Their structures were established by proton nuclear magnetic resonance (H NMR), infrared spectroscopy (IR), mass spectrometry (MS) and elemental analysis (EA). The photophysical properties were characterized by means of UV-Vis absorption spectroscopy and fluorescence spectroscopy. The results showed that in dilute dichloromethane solutions the absorbance strength of these dyads was the sum of that of their monomers, hexakishexyloxy triphenylene (HAT6) and N-hexyl-perylene monoimide dihexyl esters (PMD6), and not interfered by the length of flexible bridges. When excited at 475 nm, the strength of the fluorescence of the dyads decreased when the spacers shortened from dodecyloxy, decyloxy, hexyloxy to ethoxy groups. Actually, when the spacer was ethoxy group, the fluorescence of the dyad was almost quenched completely. This is attributed to the photoinduced electron transfer properties (PET) between the donor and acceptor units. When excited at 280 nm, the strength of the fluorescence of the triphenylene units also became weaker when the spacers shortened from dodecyloxy to ethanyloxy. At the same time, the strength of the fluorescence of the perylene units became stronger. This is attributed to energy transfer from the triphenylene unit to the perylene unit. In addition, their liquid crystalline properties have been studied by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The results demonstrated that when the spacers were decyloxy and dodecyloxy the dyads possessed columnar liquid crystal behavior in the heating cir-