Modulation of trithiophene-based chalcone positional isomers by twist angle variation: Ultrafast nonlinear optical properties and excited-state dynamics

The nonlinearities involves the interaction between multiple sources, to minimize variable factors, four trithiophene chalcone isomeric molecules were designed and synthesized to investigate the modulation of torsion angle changes (6°, 25°, 37°, 60°) on optical nonlinearities. The electronic excitation properties and relevant parameters were calculated through quantum chemical methods. Femtosecond Z-scan measurements showed that the four molecules exhibited configuration-dependent reverse saturation absorption (RSA) at 600 and 700 nm and had ≥1 figure of merit (F) at 700 nm. Combined with the orbital delocalization index, the results indicated that the spatial delocalization of electrons is gradually suppressed with system twisting. Transient absorption spectra revealed a transition from the locally excited (LE) state to the charge transfer (CT) state, and the planarized structure promotes the relaxation of excited particles. This study suggest that these novel trithiophene derivatives possess potential in nonlinear optical applications and provide an approach for the optimization of nonlinear functional isomeric materials.