Surface‐Assisted Cyclodehydrogenation and Annulative Dimerization on TiO 2 (110): Formation of an Azacoronene and Its Octagon‐Fused Dimer

Abstract

Abstract

ABSTRACT Surface‐assisted reactions on nonmetallic substrates remain much less developed than their counterparts on metals, especially for heteroatom‐doped precursors and intermolecular coupling processes. Here we show that TiO 2 (110) can support not only cyclodehydrogenation of a nitrogen‐rich nanographene precursor but also annulative intermolecular coupling on a semiconducting oxide surface. Under ultrahigh vacuum, hexapyrrolylbenzene (HPB) undergoes cyclodehydrogenation on rutile TiO 2 (110) to give unsubstituted hexapyrrolohexaazacoronene (HPHAC, 1 ). Upon further annealing, 1 undergoes dehydrogenative dimerization to form a cyclooctatetraene‐annulated HPHAC dimer ( 2 ), as supported by scanning tunneling microscopy and spectroscopy (STM/STS), density functional theory (DFT), and simulated STM images. The dimer, but not the monomer, undergoes single‐electron transfer to the substrate to form [ 2 ] •+ , consistent with STM/STS observations, its lower ionization threshold, and computed frontier orbital energies. Gas‐phase calculations are consistent with a plausible arenium‐type pathway for annulative dimer formation and further indicate that oxidation increases global aromatic character across the fused framework.