Synthesis, spectroscopic characterization, one and two-photon absorption properties and electrochemistry of pi-expanded BODIPYs dyes

Monostyryl and distyryl substituted BODIPY derivatives were synthesized by the Knoevenagel condensation reaction and fully characterized by H-1 NMR and HRMS. Their photophysical and electrochemical properties have been investigated by UV-vis absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, two-photon excited spectroscopy and cyclic voltammetry. These BODIPY dyes exhibit excellent photophysical properties in red to near-infrared region, including large extinction coefficients, high fluorescence quantum yields. They also exhibit high two-photon absorption cross sections in the 750-900 nm range. In particular, 3c presents a maximum with a sigma(2) of 2130 GM in the 750-900 nm range. In addition, the absorption and steady-state fluorescence properties in different solvents were investigated. Compounds 2b and 3b show significant positive solvatochromic fluorescence in organic solvents due to their intramolecular charge-transfer (ICT) from the aniline moiety to the BODIPY unit. All the investigated compounds undergo ring centered electron transfer by first oxidation and first reduction to generate cation and anion radicals.