Keywords:two-photon absorption, organic molecules, nonlinear spectroscopy
Borondipyrromethenes (BODIPY) are organic molecules that have a wide range of applications, such as agents in photodynamic therapy, laser dyes and even sensitizer for solar cells. This is possible due to its inherent characteristics, such as high fluorescence quantum yield, difficulty in self-aggregation, and readiness in adding secondary components to its main core. However, these molecules usually present low two-photon absorption (2PA) cross-section, of the order of 50 GM, making their nonlinear optical properties weak. It is possible to increase the 2PA cross-section of these samples by increasing its conjugation length or adding electron-donor or electron-withdrawal groups to the BODIPY main structure, as previously shown in studies. In this work, we present the two-photon absorption spectra of seven new BODIPY molecules developed at Universidade Federal de Santa Maria, which were synthesized with these conditions. The spectra were measured through an open-aperture Z-Scan technique, and then fitted by using a sum-over-states model. Quantum chemistry calculations were also done to obtain the wavelength and cross-sections of the 2PA transitions. The molecules presented 2PA cross-sections of up to 200 GM, showing an improvement in relation to previously studied BODIPYs.