Bioinspired negative-curvature monomer architecture accelerates on-surface topochemical polymerization.

Abstract

On-surface chemical reactions are often limited by competing requirements for long range molecular order and the local atomic scale dynamics needed for bond formation. In many topochemical reactions, including diacetylene photopolymerization, alkyl-chain ordering provides the required geometric registry but can also restrict the conformational motion necessary for efficient reaction. Here, we show that bioinspired phospholipid architectures accelerate topochemical polymerization at interfaces by introducing multiple, distinct forms of packing frustration that operate on both molecular and nanoscopic scales. Diacetylene phosphocholines (dPCs) and phosphoethanolamines (dPEs), when confined to striped lamellar morphologies on graphitic substrates, undergo substantially faster on-surface photopolymerization than structurally analogous 10,12-tricosadiynoic acid (TCDA) monolayers (t1/2 ~ 36 min for TCDA, 26 min for dPC, and 3 min for dPE). Molecular dynamics simulations show that topological constraints imposed by the glycerol linkage reduce alkyl-chain segmental order in both phospholipids, increasing the frequency of short separation distances between bond-forming carbons required for reaction. For dPE, typically considered a negative-curvature phospholipid, confinement to a lamellar geometry also frustrates directional headgroup hydrogen bond networks, further increasing reactivity. Together, these results identify complementary mechanisms by which topologically constrained monomers can accelerate on-surface reactions through hierarchical packing frustration. Building on this framework, we design a monomer that exhibits rapid on-surface reaction kinetics.