Two- and three-photon absorption properties of fan-shaped dendrons derived from 2,3,8-trifunctionalized indenoquinoxaline units: Synthesis and characterization

A model compound set that contains a series of fan-shaped chromophores using 2,3,8-trifunctionalized indenoquinoxaline units as the major building block of their π-framework was synthesized and characterized for their two- and three-photon absorption properties in the femtosecond regime based on two-photon-excited fluorescence and Z-scan techniques. The experimental results show that these dendritic fluorophores manifest strong and wide-dispersed two- and three-photon absorption bands within the near-infrared region, which indicates that 2,3,8-trifunctionalized indenoquinoxaline units are favorable building moieties for the construction of highly active multi-photon dyes. The maximum values of two- and three-photon absorption cross-sections for the largest dendron (i.e. compound D4) are ≈24800 GM and 6 × 10^-78 cm⁶ s², respectively. A nearly linear ascending relationship between π-structural expansion and nonlinear absorption is observed for these compounds, implying that the currently utilized structural arrangement does not exert deleterious or cooperative effects on the multi-photon absorption properties of this model system. In addition, a representative dendritic structure is selected to demonstrate efficient optical power-limiting against femtosecond laser pulses at 790 nm.