Charge transport and prototypical optical absorptions in functionalized zinc phthalocyanine compounds: A density functional study

Metal phthalocyanines are considered to be prominent candidates for designing organic semiconductors. However, enhancing n-type characteristics and air stability in these compounds have been the major challenges. Earlier studies on zinc phthalocyanines (ZnPc) reported enhancement in electron mobility due to fluorination. We present a theoretical study of the charge transfer and optical properties of functionalized zinc phthalocyanines (XZnPc, with X = F-16, Cl-16, Br-16, I-8, and (CN)(8)) within the framework of the density functional theory. Substitutions with electron-withdrawing groups at the peripheral sites of ZnPc was found to lower both E-HOMO and E-LUMO in the compounds. Computed values of electron affinity (EA) > 3 eV in all XZnPcs indicated effective electron injection inferring enhanced n-type characteristics and air stability in these compounds. However, cyanation ((CN)(8)), as compared to the other EWGs, is found to enhance the electron mobility more prominently in the compound. In addition, studied optical absorption spectra of all XZnPc compounds at different exchange-correlation functionals such as B3LYP, PBE0, CAM-B3LYP, wB97xD, M06, and M06-2X exhibited Q-band in visible region (approximate to 600-700nm) and B-band (Soret) in ultraviolet (approximate to 300-400nm) region, and a few shows an N-band below 300nm. Upon functionalization, the B-band and Q-band maxima show bathochromic shift both in gas phase and dimethyl sulfoxide. All these optical absorptions were found to be prototypical in nature, and the spectra are assigned to character.