4,9,13,18-Tetraazateropyrenes: Synthesis, Cross-Locked Saddle Packing and Unique Geometry Reorganization

Shape control in fully fused nanographenes remains challenging because rigid π-skeletons resist reorganization. Teropyrenes provide an attractive platform, but programmable shape control within this framework remains underdeveloped. Here, we report a fourfold Bischler-Napieralski annulation that affords 4,9,13,18-tetraazateropyrenes in up to 56% yield. Substituent engineering dictates both molecular shape and packing: nearly planar TATP-M forms a one-dimensional slipped π-stack, whereas saddle-shaped TATP-T adopts a distinctive cross-locked saddle dimer motif. Despite similar ground-state electronic structures and absorption profiles, the two compounds exhibit markedly different emission behaviors: TATP-M emits at 577 and 623 nm with a fluorescence quantum yield of 46.4%, whereas TATP-T shows intense red fluorescence at 625 nm with a higher quantum yield of 67.2%. Remarkably, TATP-T retains conformational adaptability after full π-extension. C₆₀ co-crystallization promotes a saddle-to-twist transformation, generating conformationally chiral P and M conformers and demonstrating C₆₀-regulated reshaping of an otherwise rigid fused backbone. Variable-temperature NMR spectroscopy and activation-barrier analysis further reveal a thermally activated, reversible exchange between conformational states. These findings establish a design principle for adaptive aza-nanographenes, in which steric, supramolecular, and thermal inputs couple molecular curvature, conformational dynamics, packing, and excited-state behavior across multiple structural and energetic dimensions.