Database of frontier molecular orbitals for diverse tetrapyrrole macrocycles

The four frontier molecular orbitals (MOs) of tetrapyrrole macrocycles determine numerous physicochemical properties, including electronic spectra, redox potentials, coordination chemistry, and sites of chemical reactivity. Here, the energies and electron distributions of the frontier MOs of ~350 tetrapyrrole macrocycles are provided. The MO characteristics have been determined by density functional theory calculations using two functionals. The MO energies can be input into a published calculational module (GOUTERMAN) for predictions and evaluation of optical spectra. The focus here is on the collection of MOs. Comparative diagrams are provided to illustrate how the MO energies change with variation in molecular characteristics. The characteristics include the following: (1) macrocycle type, (2) carbon or nitrogen atoms at the meso positions, (3) oxo/keto substitution, (4) metalation state for chlorins, (5) metalation state for bacteriochlorins, (6) substituent patterns (for porphyrins), (7) increasing π-electron delocalization (for bacteriochlorins), (8) eight common substituents versus macrocycle position (for chlorins) and (9) substituents of native chlorophylls and pheophytins. Such comparisons, the MO database, and use of the GOUTERMAN module aid in molecular design of tetrapyrrole chromophores for use as stand-alone pigments or in multipigment arrays. The insights underpin the analysis of the electronic properties of these architectures and consequent ground- and excited-state processes.