Structures and properties of novel 5,15-di[4-(5-acetylsulfanylpentyloxy) phenyl] porphyrin derivatives: Density functional theory calculations

Density functional theory (DFT) calculations have been carried out in order to compare the molecular structures, atomic charges, molecular orbitals, electronic absorption spectra, and infrared (IR) spectra of the metal-free 5,15 -di[4-(5-acetylsulfanylpentyloxy) phenyl]porphyrin H₂[DPP(OC ₅H₁₀SCOCH₃)₂] (1) (DPP = 5,15-diphenylporphyrin) and its zinc complex Zn[DPP(OC₅H ₁₀SCOCH₃)₂] (2), which exhibit novel structures with two 5-acetylsulfanylpentyloxy side chains at the para-positions of opposite meso-attached phenyl groups. The calculated molecular structure and electronic absorption and IR spectra of 1 and 2 are consistent with the experimental results. The influences of meso-substitution, polar solvents, and central metal substitution on the structure and properties of porphyrin derivatives have been investigated by comparing the corresponding data for 1 and 2 with the help of data for the unsubstituted porphyrin derivatives, namely the metal-free porphyrin H₂Por (3) and the porphyrinato-zinc compound (4). The identities of the main transitions in the electronic absorption spectra of 1 and 2 are assigned and the vibrational modes in their IR spectra are identified with the assistance of animated pictures produced based on normal coordinates. The theoretical work presented here will be helpful in increasing our understanding of the structure and spectroscopic properties, as well as substituent and solvent effects, for these novel porphyrin compounds.