Zwitterionic Bergman-Triggered Cascade Polymerization: A Plateau Reaction Leading to Metal-Graphene Nanoribbon Semiconductors Using Boron-Metal Couple

Abstract

With a rapid growth in artificial intelligence, designing high-speed and low power semiconducting material is of utmost importance. This investigation provides a theoretical basis to access covalently-bonded transition metal-graphene nanoribbon (TM-GNR) hybrid semiconductors whose DFT-computed bandgaps were much narrower than the commonly used pentacene. A systematic optimization of substrates containing remotely-placed boronyl groups and the transition metals produced the zwitterions via ionic Bergman cyclization (i-BC) and unlocked the polymerization of metal-substituted polyenynes. Aside from i-BC, the subsequent steps showed plateau-TS involving structureless transition regions. A multivariate analysis revealed a strong dependence of activation energy and the cyclization mode on the electronic nature of boron and Au(I). Consequently, three regions corresponding to radical Bergman (r-BC), ionic Bergman (i-BC), and ionic Schreiner-Pascal (i-SP) cyclizations were identified. The boundaries between these regions corresponded to the mechanistic shift induced by three-center-three-electron (3c-3e) hydrogen bond, three-center-four-electron (3c-4e) hydrogen bond, and vacant p-orbital on boron. The ideal combination for cascade polymerization was observed near the boundary between i-BC and i-SP.