Interaction of meso-Tetraphenylporphines with C60 Fullerene: Comparison of Several Density Functional Theory Functionals Implemented in DMol3 Module

We performed DFT calculations of noncovalently bonded complexes (or dyads) of metal-free mesotetraphenylporphine H2TPP and its complexes Co(II)TPP and Ni(II)TPP with fullerene C-60, using PW91, PBE and BLYP functionals of general gradient approximation (GGA), as well as PWC and VWN functionals of local density approximation (LDA) implemented in the DMol3 module of Materials Studio package, in conjunction with the DNP basis set. The results obtained are analyzed in order to estimate how realistic they are, what differences and similarities they have. We found that none of five functionals tested matches well enough the experimentally observed separations between porphyrin and fullerene units; the experimental separations turn to be in between those calculated by PW91 and PBE GGA and those obtained by PWC and VWN LDA. BLYP produces totally unrealistic values for all the dyads, reaching almost 5 angstrom in the case of NiTPP + C60. Laser desorption/ionization time-of-flight (LDI-TOF) mass spectrometry of mechanical porphyrin/fullerene mixtures was employed to roughly estimate relative stability of the porphyrin-C-60 dyads. In the case of H2TPP + C-60 and NiTPP + C-60 we observed much weaker complexation (estimated as the dyad peak intensity attributed to the intensity of porphyrin peak) as compared to the case of CoTPP + C-60. Apparently, the closed-shell systems behave similarly to each other and different to the paramagnetic Co complex, which matches better the formation energies found from LDA calculations.