Electronic structure of Zn-chlorin π-anions studied by spectroscopic and quantum-chemical methods

Electronic structure of neutral Zn‐chlorin complexes and their π‐mono‐ and dianions has been considered. The π‐anions were obtained by reduction of neutral chlorins with a sodium mirror in tetrahydrofuran solution. Results of spectroscopic studies have been compared with semiempirical quantum‐chemical calculations. Characteristic bands in electronic absorption spectra of the uv, visible and near infrared regions are in good agreement with CNDO/S‐CI calculations. Partially resolved hyperfine structure in EPR spectra of π‐radical anions was observed. Parameters of the EPR spectra obtained by using the simulation technique were compared with spin densities calculated by the INDO method. The detailed interpretation of 1H and 13C NMR spectra of neutral and dianion Zn‐octaethylchlorins is presented. All the proton signals in π‐dianions are shifted upfield because of the influence of paramagnetic ring current. The upfield shifts in 13C NMR spectra of the species studied have been observed too, except for two carbon atoms of the pyrrole ring being placed opposite the hydrogenated one. The 13C peak positions correlate with the charge distribution on C atoms in neutral molecules as well as in π‐dianions. © 1995 John Wiley & Sons, Inc.