Design of Coupled Porphyrin Chromophores with Unusually Large Hyperpolarizabilities

A new series of push–pull porphyrin-based chromophores with unusually large static first hyperpolarizabilities are designed on the basis of coupled-perturbed Hartree–Fock and density functional calculations. The proper combination of critical building blocks, including a ruthenium(II) bisterpyridine complex, proquinoidal thiadiazoloquinoxaline, and (porphinato)zinc(II) units, gives rise to considerable predicted enhancements of the static nonlinear optical (NLO) response, computed to be as large as 11 300 × 10–30 esu, 2 orders of magnitude larger than the benchmark [5-((4′-(dimethylamino)phenyl)ethynyl)-15-((4″-nitrophenyl)ethynyl)porphinato]zinc(II) chromophore. A two-state model was found to be useful for the qualitative description of the first hyperpolarizabilities in this class of NLO chromophores, which are predicted to have hyperpolarizabilities approaching the fundamental limit predicted to be attainable by empirical theoretical models.