Bis(azidophenyl)phosphole building block for extended π-conjugated systems

Novel bis(azidophenyl)phosphole sulfide building block 8 has been developed to give access to a plethora of phosphole-containing π-conjugated systems in a simple synthetic step. This was explored for the reaction of the two azido moieties with phenyl-, pyridyl- and thienylacetylenes, to give bis(aryltriazolyl)-extended π-systems, having either the phosphole sulfide (9) or the phosphole (10) group as central ring. These conjugated frameworks exhibit intriguing photophysical and electrochemical properties that vary with the nature of the aromatic end-group. The λ ³-phospholes 10 display blue fluorescence (λ _em = 460-469 nm) with high quantum yield (φ _F = 0.134-0.309). The radical anion of pyridyl-substituted phosphole sulfide 9b was observed with UV/Vis spectroscopy. TDDFT calculations on the extended π-systems showed some variation in the shape of the HOMOs, which was found to have an effect on the extent of charge transfer, depending on the aromatic end-group. Some fine-tuning of the emission maxima was observed, albeit subtle, showing a decrease in conjugation in the order thienyl < phenyl < pyridyl. These results show that variations in the distal ends of such π-systems have a subtle but significant effect on photophysical properties. We report a novel approach to phosphole-containing π-conjugated materials. From bis(azidophenyl)phosphole 8, a plethora of π-conjugated systems are possible in a single step, incorporating different aromatic capping groups installed using click chemistry. End-group variations introduce photophysical and electronic changes into resulting fluorophores 10, which have been investigated in detail.