Synthesis and characterization of 5,10,15,20-tetra (N-ethyl-3-carbazoyl) porphyrin

Abstract

The newly prepared 5,10,15,20-tetra(N-ethyl-3-carbazoyl) porphyrin is characterized by ¹H NMR, FAB-HRMS, UV-visible spectrophotometry, fluorescence spectrometry, and electrochemistry. The porphyrin display an extinction coefficient of 2.8 × 10⁵ cm⁻¹M⁻¹ for the Soret band at 433 nm. Three Q bands have been also observed at 523, 563, and 655 nm with corresponding extinction coefficients given as 1.3 × 10⁴, 1.1 × 10⁴, and 5.6 × 10³ cm⁻¹M⁻¹. Excitation at 433 nm gives an emission line at 662 nm. The quantum yield has been determined to be 0.09. Cyclic voltammetry has been used to determine the oxidation and reduction potentials of the new porphyrin. Two quasi-reversible one-electron oxidations have been observed at 0.862 and 1.010 V and a quasi-reversible reduction of the chromophore has been observed at -1.186 V versus the standard calomel electrode with tetrabutylammonium tetrafluoroborate as the supporting electrolyte. Carbazole is an electron donating group covalently attached to the porphyrin in the meso positions. Trends observed in the oxidation and reduction potentials are consistent with the nature of the porphyrin. That is, the electron donating group in 5,10,15,20-tetra(N-ethyl-3-carbazoyl) porphyrin enhances oxidation and inhibits reduction.