Synthesis and Optical Properties of 2‐(Benzo[b]thiophene‐3‐yl)pyrroles and a New BODIPY Fluorophore (BODIPY=4,4‐Difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene)

The light fantastic: Two new 2‐(benzo[b]thiophene‐3‐yl)pyrroles have been synthesized, and are shown to exhibit optical properties that are promising for optoelectronic materials and devices such as highly efficient fluorescent sensors (see scheme). In addition a new BODIPY fluorophore, derived from 2‐(benzo[b]thiophene‐3‐yl)pyrrole, was also isolated and shows good spectroscopic properties in solution which are fully preserved in the solid state. 2‐(Benzo[b]thiophene‐3‐yl)‐1‐vinylpyrrole has been synthesized directly from 3‐acetylbenzo[b]thiophene oxime and acetylene (flow system, KOH‐DMSO, 120 °C, 5 h) in 68 % yield. Devinylation of the synthesized pyrrole (Hg(OAc)2, NaBH4, 50 °C) led to the corresponding 2‐(benzo[b]thiophene‐3‐yl)pyrrole in 63 % yield. Trifluoroacetylation of both the pyrroles with trifluoroacetic anhydride (80 °C, 1 h) gave the corresponding 5‐trifluoroacetyl pyrroles in 97 % and 76 % yields, respectively. 2‐(Benzo[b]thiophene‐3‐yl)pyrrole was reacted subsequently with mesityl aldehyde, 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ), and BF3⋅OEt2 to afford 4,4‐difluoro‐3,5‐di(benzo[b]thiophene‐3‐yl)‐8‐mesityl‐4‐bora‐3a,4a‐diaza‐s‐indacene, a representative of the novel BODIPY fluorophore family (BODIPY=4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene), in 34 % overall yield. The synthesized pyrroles exhibit promising optical properties (absorption and emission spectra, nonlinear optical (NLO) features), superior to existing analogues. The BODIPY fluorophore displays an intense red‐shifted fluorescence emission in CH2Cl2 (625 nm, 0.84 fluorescence quantum yield) that is fully preserved in the solid state. The light fantastic: Two new 2‐(benzo[b]thiophene‐3‐yl)pyrroles have been synthesized, and are shown to exhibit optical properties that are promising for optoelectronic materials and devices such as highly efficient fluorescent sensors (see scheme). In addition a new BODIPY fluorophore, derived from 2‐(benzo[b]thiophene‐3‐yl)pyrrole, was also isolated and shows good spectroscopic properties in solution which are fully preserved in the solid state.