Expanded π-electron systems, tri(phenanthro)hexaazatriphenylenes and tri(phenanthrolino)hexaazatriphenylenes, that are self-assembled to form one-dimensional aggregates

This paper reports the self-assembling and electrochemical nature of hexaazatriphenylene-based electron-deficient heteroaromatics with an expanded π-electron system. The tri(phenanthro)hexaazatriphenylenes (TPHAT-Cs) and tri(phenanthrolino)hexaazatriphenylenes (TPHAT-Ns) were prepared by condensation reactions of the corresponding phenanthrenequinones and phenanthrolinediones, respectively, with hexaaminobenzene. Their electron affinity was indicated from cyclic voltammetry measurements, in which the first reduction potentials were evaluated at around -1.7 V (vs Fc/Fc⁺) in dichloromethane. In nonpolar and polar solvents and in the film state, the TPHAT-Cs and TPHAT-Ns formed one-dimensional aggregates with an H-type parallel stacking mode. In the MALDI-TOF mass spectra, significant peaks were seen at several multiples of the parent ion up to tetramer aggregates. The ¹H NMR spectra indicated a line-broadening effect due to the aggregation. The UV-vis and fluorescence spectra showed a concentration dependence, which is attributed to a dynamic exchange between the monomer and aggregate species. The order of the aggregative nature was estimated from the concentration dependence and the fluorescence quantum yield. By replacement of the peripheral aromatic moieties instead of the phenanthrene (TPHAT-Cs) with the phenanthroline (TPHAT-Ns), the aggregative nature was enhanced.