TriQuinazoline and Related Quinoline/Quinazoline Cyclic Trimers: Unified Synthesis, Planar Discotic Architecture, and Proton Dynamics in an Atomic-Scale Cavity

Heteroatom-doped graphitic materials, particularly those bearing nitrogen, have attracted considerable attention because of their unique physicochemical properties, which are unattainable in pristine carbon frameworks. To rigorously investigate the effects of doping and to enable fine-tuning of their functions at the atomic scale, bottom-up synthesis of well-defined molecular surrogates provides a powerful approach. Herein, we report the design, synthesis, and physicochemical characterization of a series of quinoline/quinazoline cyclic trimers, TriQuinoline (TQ, Q3), Q2Qz1, Q1Qz2, and TriQuinazoline (TQz, Qz3), featuring an atomic-sized central cavity surrounded by three pyridinic nitrogens that mirrors the local topology of nitrogen-doped graphene defects. A modular synthetic strategy enabled facile access to all of the quinazoline-containing congeners. Systematic X-ray analysis and computational studies revealed increasing molecular planarity with increasing quinazoline incorporation, arising from stepwise elimination of destabilizing CH···HC contacts and the emergence of favorable CH···N interactions. Spectroscopic and theoretical studies demonstrated that quinazoline substitution progressively decreases the proton affinity at the central cavity owing to the electron-withdrawing nature of the quinazoline units, which markedly accelerates proton exchange. Even with these electronic modifications, supramolecular association with polycyclic aromatics, such as coronene and [12]cycloparaphenylene ([12]CPP), substantially remained preserved upon quinazoline incorporation. These findings highlight the cooperative interplay of structural planarity and heteroatom substitution in dictating the properties of discotic heteroaromatics, offering a versatile platform for material design.