Synthesis, Structure, and Photothermal Conversion of a Bowl-Shaped Nanographene Containing Fused 5-/7-Ring Pairs

Incorporation of non-hexagonal topologies into bowl-shaped nanographenes offers opportunities for tailoring their electronic properties and supramolecular behavior, however synthesis of such curved systems remains challenging. Herein, we report the facile synthesis of a bowl-shaped nanographene (TAT) embedded with three circularly fused pentagon-heptagon (5/7) pairs via a three-fold intramolecular Heck reaction. Its concave geometry is verified by nuclear magnetic resonance (NMR) spectroscopy, high resolution mass spectrometry, and x-ray crystallography. Variable-temperature ¹H NMR studies reveal a low bowl-to-bowl inversion barrier of 13.5 ± 1.3 kcal·mol^-1, enabling its fast dynamic motion even at room temperature. UV-vis absorption spectroscopy and cyclic voltammetry demonstrate a narrow energy gap, reflecting its highly delocalized π-conjugation system. The concave geometry of TAT allows it to co-assemble with fullerenes, forming a 2:1 complex with C₆₀ as confirmed by single-crystal x-ray diffraction analysis. Furthermore, femtosecond transient absorption spectroscopy reveals its ultrafast nonradiative excited-state deactivation process. Benefiting from this photophysical behavior, water-soluble nanoparticles of TAT encapsulated in an amphiphilic polymer achieve a high photothermal conversion efficiency of 41%. This work establishes a bottom-up strategy for synthesizing an unprecedented bowl-shaped nanographene and provides insights into its intrinsic optoelectronic, supramolecular properties, and photothermal conversion potentials.