One-Pot Synthesis of Brightly Fluorescent Mes₂B‑Functionalized Indolizine Derivatives via Cycloaddition Reactions

Four new BMes2-functionalized indolizine derivatives (Mes = mesityl) have been prepared via the cycloaddition reaction between pyrido­[2,1-a]­isoindole (A) or pyrrolo­[1,2-a]­pyridine (B) and BMes2-containing alkynes. All four compounds are brightly blue or blue-green fluorescent with λem = 428–495 nm and Φ = 0.27–0.68, depending on the substitution position of the BMes2 group. Experimental and TD-DFT computational data indicated that the primary electronic transitions responsible for the fluorescence of 1–4 are from HOMO to LUMO (π → π*) rather than charge transfer from N → B, which is in agreement with previous findings suggesting that the lone-pair on N is delocalized throughout the N-heterocycles.