Design and physico-chemical properties of unsymmetrically substituted dipyrromethenes and their complexes with boron(III) and zinc(II)

Abstract

Unsymmetrically substituted boron(III) and zinc(II) dipyrromethenates were synthesized in high yields, and the physico-chemical investigation results of them are presented. Comparative analysis of luminescence properties in a series of various organic solvents, photo- and thermal stability was carried out depending on the molecular structure. For the first time it was established that the methyl group absence in α-, β- or β′-position of one of the pyrrole fragments changes properties of pentamethyl-dipyrromethene ligands and complexes differently. It is shown unsubstituted α- or β-position of one pyrrole cycle leads to a hypsochromic shift of the maximum of the intense absorption band and free β′-position – to bathochromic shift. In the general case, the fluorescence quantum yield of BODIPY reaches 99% and depends little on the solvent properties. However, BODIPY unsubstituted in one of the α-position showed a sharp decrease of the fluorescence quantum yield upon going from non-polar solvents to polar. Unsymmetrically substituted zinc(II) dipyrromethenates are characterized by low value of the fluorescence quantum yield, the fluorescence almost completely quenching in weakly polar and polar solvents. It is found that the unsymmetrically substitution increases photostability of boron(III) and zinc(II) complexes but decreases their thermal stability in solid state.