Polycyclic Arene-Fused Selenophenes via Site Selective Selenocyclization of Arylethynyl Substituted Polycyclic Arenes

Arene-fused selenophenes were synthesized by a redox neutral process from arylethynyl substituted polycyclic arenes using selenium powder in refluxing N-methyl-2-pyrrolidone (NMP) with the assistance of the residual water in NMP as a catalytic proton source. The site-selective nature of this selenocyclization produces trans-alkenes as a competitive product, which is dependent on the π-electron donation ability of polycyclic arenes and the kind of arylethynyl group attached to it. DFT calculations were performed to understand the site selectivity in the selenophene formation reaction. The HOMO coefficient on the carbon adjacent to carbon having arylalkyne substituent of the polycyclic arene correlates with the selenocyclization tendency of the substrate. The wavelength of absorption and emission and quantum yield of emission increase with increasing the number of fused benzene rings in the polycyclic unit (from naphthalene to pyrene).