Aza‐BOIMPYs: A Tetrazole Auxochrome for Highly Red‐Emissive Dipyrromethene‐Based Fluorophores

A structural derivative of the recently designed BOIMPY motif is introduced; this derivative engages a meso tetrazole moiety and a dipyrromethene scaffold in a twofold BF2‐coordination scheme. A one‐pot synthesis allows the isolation of unusual dipyrro‐perazafulvene precursors and subsequent access to nonfluorescent mono‐BF2 and fluorescent bis‐BF2 species. The novel fluorophore, denoted Aza‐BOIMPY, is highly emissive (ΦF up to 0.82), structurally compact, and provides useful inherent polarity. Absorption and emission events focus at roughly 600 nm with exceptionally small Stokes shifts (209 cm−1) and high attenuation coefficients (up to 120 000 m−1 cm−1). X‐ray crystallographic and computational investigations provide insights into geometrical and electronic properties of the novel dye type. A tribute to compactness: A tetrazole bridging ligand serves as a novel auxochrome for the recently introduced twofold BF2‐complexation strategy of dipyrromethene motifs. A short synthetic route provides access to compact, amphiphilic, and photostable fluorophores of high brightness.