‘Ethoxy axial ligand’ strategy: A structural modification of molybdenum(V) porphyrins to enhance photophysical properties

The issue of optimizing molecular structures for photoactive metalloporphyrins (MPs) is relevant to fields like optoelectronics, sensing, and medicine. The enhanced activity of axial positions in molybdenum(V) porphyrin complexes opens up new possibilities for synthesizing compounds and systems with optimal photochemical and photophysical parameters for their molecular materials. To understand the role of axial substitution in the sensitivity to organic bases and potential charge transfer in the MP — base dyad, we studied how replacing the hydroxy ligand with an ethoxy ligand in the (hydroxy)(oxo)(5,10,15,20-tetraphenylporphinato)molybdenum(V) (O[Formula: see text]Mo(OH)TPP) structure affects its properties, as the ethoxy ligand displays positive electronic effects in organic compounds. O[Formula: see text]Mo(OH)TPP and O[Formula: see text]Mo(OEt)TPP, along with their coordination dyads with N-methyl-2-(pyridin-4-yl)-3,4-fullero[60]pyrrolidine (PyF), were synthesized and characterized structurally using UV–vis spectroscopy, IR spectroscopy, 1 H NMR, and MALDI TOF methods. The photophysical properties of the dyads were examined through femtosecond transient absorption spectroscopy and fluorescence. We provided a complete kinetic description of the self-assembly in mixtures of molybdenum(V) porphyrin complexes with the fullerene base in solution and the dynamics of ultrafast processes in the resulting dyads upon photoexcitation.