Competing third- and fifth-order optical nonlinearities in push–pull anthracenyl chalcones probed by intensity-dependent femtosecond Z-scan

Strategic modification of molecular structures for optimized nonlinear optical (NLO) responses requires an understanding of the charge transfer mechanisms that govern the optoelectronic properties. This work systematically examines the structure-NLO relationship in polycyclic aromatic hydrocarbons (PAHs)-based chalcone derivatives focusing on effective design strategies such as extending ?-conjugation and incorporating strong electron-donating/withdrawing substituents. Three anthracenyl chalcones with aroyl terminal groups of naphthalene (3AP35), benzofuran (3AP40), and p-cyanophenyl (MTP100) were subjected to femtosecond Z-scan measurements under input intensity variation from 49.87 to 93.50 GW cm-2 using 800 nm laser excitation. Consistent ?2 values derived across all intensities for 3AP35 and MTP100 signify the pure two-photon absorption (2PA) process. Whereas the deviating ?2 values in 3AP40 were discovered to arise from fifth-order NLO contributions, resulting in a transition from pure-2PA to 2PA-induced excited-state absorption (2PA-ESA) beyond 56.10 GW cm-2. Separate fitting equations were explicitly used to model the third- and fifth-order NLO processes and to extract their corresponding nonlinear absorption coefficients (?2 and ?3). Molecules exhibiting a lower magnitude of solvatochromic shifts showed weakest NLO responses, while the strongest responses correlated with the greatest sensitivity to solvent polarity. Wavefunction analysis revealed a stronger push-pull character, a lower HOMO-LUMO gap, and greater electron delocalization, which are associated with a reduced optical energy gap and enhanced molecular polarizability. This work investigates the electronic process underlying the NLO response in PAH-based chalcones, which combine ?-conjugation extension with strategic donor-acceptor modulation, providing new insights into materials development for photonic applications. © 2026 Elsevier B.V.