Design and photophysical investigation of dipyrromethenates coordinated with the boron(III), zinc(II) and cadmium(II) as optical elements

Abstract Alkyl-halogen-dipyrromethene (Dpm) ligands coordinated with boron(III), zinc(II), and cadmium(II) were studied experimentally and theoretically to elucidate and compare influence of the coordination centers and halogen substituents (“heavy” atom effect) on observable photophysical properties. Novel and recently published experimental data were summarized and analyzed using quantum-mechanical calculations which revealed specific of the electronic structures and photo-induced dissipations in the molecular complexes. Halogenation of the Dpm difluoroborates (BODIPY) increases the intersystem spin crossing (ISC) and the triplet harvest whereas halogen atoms play no crucial role in fluorescence quenching of the systems with Zn(II) and Cd(II) complexing agents. Low fluorescence intensities of double Dpm moieties coordinated with the transition metal ions are provided by radiationless internal conversion suppressing photoemission with following ISC which is intensified in presence of halogens. BODIPY fluorescence undergoes direct ISC competition and quenching intensity depend on the kind and the number of halogens.