The influence of fluorene-bridge connecting strategies on charge transfer and photoabsorption characteristics of multi-branched oligomers

Abstract

This study computationally investigates novel tri-branched D–π–A oligomers featuring fluorene-based π-bridges with distinct topologies. Combined DFT/TD-DFT calculations reveal how the bridge structure critically governs two-photon absorption (TPA) performance. Significantly, the fused fluorene bridge (in TRZ-3) enhances the TPA response twofold and redshifts the band beyond 700 nm compared to the conventional direct-link analog (TRZ-1) under comparable conjugation. This demonstrates that strategic π-bridge design, particularly fusion, dramatically optimizes the TPA properties. The established structure–property relationship provides vital design principles for advanced nonlinear optical materials.