Synthesis of Benzofuran-Embedded Selena- and Telluraporphyrins

The benzofuran-embedded selena-and telluraporphyrins are resulted by replacing the pyrrole ring that is across the selenophene/tellurophene ring in meso-tetraaryl 21-selenaporphyrin and 21-telluraporphyrin respectively by a benzofuran unit. Three examples of benzofuran-embedded selenaporphyrins and one example of benzofuran-embedded telluraporphyrin were synthesized by adopting a simple 3 + 2 synthetic protocol involving the condensation of benzofuran based tripyrrane with appropriate 2,5-bis(hydroxymethylaryl) selenophene/telluorophene to afford pure benzofuran-embedded selenaporphyrins and telluraporphyrin in 3-6% yields. The macrocycles were thoroughly characterized and studied by various spectroscopic and computational techniques. The spectral and computational studies certified their nonaromatic nature unlike aromatic meso-tetraaryl 21-selena/21-telluraporphyrins, which proves that replacement of pyrrole with a benzofuran ring results in complete alteration of electronic properties. The DFT studies revealed that the benzofuran moiety hinders pi-electron delocalization in the macrocycle due to its inflexibility, and the macrocycles adopt highly deformed saddle-shaped structures. The absorption spectra of benzofuran-embedded selena-and telluraporphyrins showed one strong band at -,350-380 nm and one broad band at -,650-695 nm that extended up to -,900 nm. However, the protonated derivatives of macrocycles absorb strongly in the NIR region with a band trailing up to 1200 nm. The electrochemical studies revealed that the macrocycles are electron deficient, and theoretical studies resembled the experimental observations.

Automated summary

The benzofuran-embedded selena- and telluraporphyrins were synthesized through replacing the pyrrole ring with a benzofuran unit, resulting in altered electronic properties. The presence of the benzofuran moiety in the macrocycles led to distorted structures and hindered pi-electron delocalization. The absorption spectra showed strong bands in the visible range for the benzofuran-embedded selena- and telluraporphyrins, while the protonated derivatives exhibited strong absorption in the near-infrared region.