3,5-diaryl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyes: Synthesis, spectroscopic, electrochemical, and structural properties

This research was undertaken to obtain new "BODIPY" dyes that fluoresce at relatively long wavelengths. The title compounds 1a-e were prepared via a d ivergent route involving Suzuki couplings of arylboronic acids to N-tert-bu toxycarbonyl-4-bromopyrrole 2, condensation of the products with an acid ch loride, and incorporation of the boron difluoride entity. Two alkyl-substit uted systems 7a and 7b were also prepared for comparison; the critical diff erence between structures 1 and 7 is that the former have an aryl group att ached to each pyrrole nucleus whereas the latter only have alkyl substituen ts on that same ring. UV absorption and fluorescence emission data were com pared for compounds 1 and 7. Absorption and fluorescence emission maxima fo r compounds 1 occur at higher wavelengths than for compounds 7, and the Sto kes shifts for the aryl-substituted compounds 1 are larger than for the alk yl-substituted compounds 7. Fluorescence quantum yields measured for compou nds 1 are less than for compounds 7, and possible reasons for this are outl ined. Other physical data for the compounds were also collected. Oxidation and reduction potentials of the systems were obtained from cyclic voltammet ry experiments, and a single-crystal X-ray structure determination was perf ormed for the bisnaphthyl-substituted compound 1b.