Stability, electronic, optical and vibrational spectra of copper octa-fluorophthalocyanine (F8CuPc) and its conformations : A DFT/TDDFT study

Abstract

We report on the energetics of formation, geometric optimization, ionization energies, Ultraviolet–visible (UV–Vis) spectroscopy, vibrational frequency analysis, and electronic properties of pristine Copper octa-fluorophthalocyanine (F₈CuPc) and its four different conformations as obtained using the ground-state density-functional theory (DFT) and time-dependent density-functional theory (TDDFT) approaches. The conformations have been constructed by permutation and substitution between fluorine and hydrogen atoms of the F₈CuPc. Based on the calculated formation energy, we found that one of the conformations, termed ’A’, is the most stable, and is even more stable than the widely known pristine F₈CuPc. Our vibrational analysis show an absence of imaginary frequencies thus suggesting the stability of F₈CuPc and its four conformations. The structural parameters obtained for the conformations are consistent with the available experimental and theoretical data. Across the conformations, the band gap, E${}_g$ varies. Of particular interest is the $E_g$= 0.80 eV obtained for the most stable conformation A. Such a value of band gap makes this conformation of F₈CuPc suitable for absorbing sunlight in the near-infrared region thereby making it useful for harvesting energy from this part of the solar spectrum. More interestingly is the fact that the electronic and optical properties of this important molecule, i.e Fe₈CuPc can be tuned by permutations of the constituents atoms of fluorine and hydrogen. This opens the possibility of functionalization of surfaces or nanostructures with the conformations, for specific applications.