Remarkable Effect of Odd–Even Spacer in Supramolecular Polymerization and Piezoresponse of Amide‐Functionalized Naphthalene Diimides

Abstract

ABSTRACT This study reports an unprecedented odd–even spacer‐length effect on the supramolecular polymerization and piezoelectricity of a series of amide‐functionalized naphthalene‐diimide (NDI) derivatives. By varying the number of methylene units ( n  = 1–4) in the linker between the NDI‐core and the hydrogen‐bonding amide group, we demonstrate that the parity of the spacer dictates the stability, internal‐order, gelation, and functionality of the supramolecular polymers. Even‐spacer derivatives exhibit significantly higher thermal stability, melting points, and gel‐phase elasticity compared to their odd‐spacer counterparts. Supramolecular polymerization for all derivatives follows a nucleation‐elongation pathway; however, even‐spacer monomers display markedly higher cooperativity and also favor more stable elongation. Molecular dynamics (MD) simulations elucidate the structural origin of these differences: even‐spacer derivatives adopt a tightly packed helical π‐stacking pattern that results in the cancellation of the in‐plane dipoles. In contrast, odd‐spacer derivatives form linear, offset stacking motifs where individual dipoles align and accumulate, leading to highly polarizable supramolecular polymers. This divergence in the internal dipole orientation translates into a dramatic odd–even effect on the piezoelectric dipolar hysteresis. Odd‐spacer derivatives exhibit remarkably high positive piezoelectric coefficients (maximum d 33 ∼ 75 pm/V), whereas even‐spacer systems show much weaker, and rarely reported negative responses (minimum d 33 −15 pm/V).