Theoretical study on the design of Y6 non-fused ring derivatives via non-covalent conformational locks

Abstract

While nonfused ring non-fullerene acceptors (non-fused ring NFAs) have emerged as promising candidates for organic photovoltaics owing to their streamlined synthetic routes and cost-effectiveness, their practical applications remain constrained by intrinsic molecular non-planarity. Herein, we propose a conformational lock engineering strategy through non-covalent interactions to construct a novel non-fused ring NFA system featuring unprecedented planarity and structural rigidity. Building upon the A1-D-A2-D-A1 architecture of the star fused-ring acceptor Y6, we systematically engineered eight non-fused-ring derivatives (Y6-1 to Y6-8) by strategically implementing non-covalent interactional lock (NoCL) modifications at the central D-unit. Comprehensive density functional theory (DFT) calculations quantified the NoCL strength through second-order natural bond orbital energies E(2) and the molecular descriptor of NoCLs (S), while simultaneously evaluating optoelectronic parameters. All derivatives demonstrated extended absorption coverage in the near-infrared region (733.92–962.03 nm) via bathochromic shifts, accompanied by optimized bandgaps (1.52–2.40 eV) favorable for charge dissociation. Notably, Y6-1 and Y6-4 demonstrate exceptional characteristics: (1) the lower electron reorganization energies (0.138 eV and 0.130 eV); (2) optimized energy level alignment with Fermi levels approaching conduction bands, and (3) the strong intramolecular non-covalent interactions exhibit E(2) values (−2.27 kcal mol⁻¹ and −1.07 kcal mol⁻¹), with corresponding S values (0.235 and 0.253). Theoretical device simulations of PM6:Y6-1/4 blends achieved higher fill factors (0.90 and 0.91) and open-circuit voltages (1.29 V and 1.34 V), surpassing conventional non-fused ring NFA based devices. This work provides a beneficial supplement to the NoCL theoretical design of Y-series electron acceptors, addresses long-standing performance limitations in non-fused ring NFAs, and paves the way for cost-effective organic photovoltaic technologies.