Yijia Chen, Wendan Luo, Ke Liu*, Taihong Liu*, Liping Ding, and Yu Fang. Chin. J. Struct. Chem., 2025, DOI: https://doi.org/10.1016/j.cjsc.2025.100704

Correlation between tunable optical properties and push-pull structural characters have attracted extensive attention in material science and nonlinear optics. Here, several indacenodithiophene (IDT) derivatives denoted as IDT-2NA, NA-IDT-CN, and IDT-2CN with different terminal substituents were investigated comparatively to demonstrate their intrinsic structure-property relationships. Interestingly, the IDT core act diverse roles as acceptor (A) and donor (D) in the obtained three derivatives. Symmetric IDT-2NA with a D-A-D architecture showed an absorption maximum around 459 nm in THF. Contrary to the symmetric analog IDT-2CN with a reverse A-D-A feature, NA-IDT-CN with a different D-D¢-A motif characterized an obvious solvent polarity effect. Theoretical calculation and electrostatic potential results confirmed the terminal substituents with different electronic conjugation play vital roles in affecting the resultant photophysical properties. Utilizing the femtosecond open-aperture Z-scan technique, significant two-photon absorption (2PA) capabilities were obtained ranging from 540 to 900 nm. The 2PA cross section (δ_2PA) maximum about 5390 GM of centrosymmetric IDT-2CN exhibited at 600 nm. Distinct excited-state dynamics with the help of femtosecond transition absorption supported the effective intramolecular charge transfer which account for enhancing δ_2PA values. Their potential optical limiting applications based on the 2PA mechanism were further evaluated. The limiting thresholds were found to be 2.79-3.35 mJ/cm² for the three IDT derivatives with a sequence of IDT-2CN<IDT-2NA<NA-IDT-CN. The distinct structural motifs and effective 2PA capabilities in the current work may provide reliable insights into the push-pull IDT chromophores for advanced nonlinear optical applications.

Figure 1. Frontier molecular orbital distributions and ESP maps of the IDT derivatives with different molecular motifs.

Figure 2. Nonlinear optical properties of the IDT derivatives.

First Author: Chen Yijia, master’s student, Shaanxi Normal University.

Correspondence Authors: Assoc.Prof. Liu Taihong, Shaanxi Normal University; Assist. Prof. Liu Ke, Northwest A&F University

Full Text Link: https://doi.org/10.1016/j.cjsc.2025.100704