Dramatically enhanced broadband reverse saturable absorption of anthracene derivatives: Regulatory effect of π-bridge in two-branched molecules

Polycyclic aromatic hydrocarbons (PAHs) are widely employed in laser protection applications owing to their excellent nonlinear optical absorption (NLA) properties. Nevertheless, the underlying enhancement mechanisms governing their NLA performance, particularly concerning structure-property relationships, remain ambiguous. To study the influence of π-bridges on nonlinear optical absorption (NLA) performance and excited-state dynamics, we designed and synthesized three two-branched anthracene derivatives (ZN1, ZN2, and ZN3) in this work. By introducing different π-bridges, we modulate the dihedral angle θ between the anthracene core and side chains in these two-branched molecules from 90° to 0°, thereby governing their electron transition characteristics. Through an integrated computational-experimental framework, we elucidate the distinct excitation pathways in these systems—including intramolecular charge transfer (ICT) and local excitation (LE)—by employing hole-electron analysis and transient absorption spectroscopy. Reducing the dihedral angle θ facilitates orbital overlap between the conjugated core and side chains, which extends the π-conjugated system and significantly augments the molecule's reverse saturable absorption (RSA) performance. Based on the above molecular optimization strategy, we have successfully improved the ultrafast broadband optical limiting (OL) performance of these compounds (515–650 nm), with an OL threshold as low as 9.11 mJ/cm².