Acetylenyl-linked, porphyrin-bridged, donor-acceptor molecules: A theoretical analysis of the molecular first hyperpolarizability in highly conjugated push-pull chromophore structures

We described the theoretical basis for the exceptionally large molecular first hyperpolarizabilities inherent to (5,15-diethynyl)porphinato)metal-bridged donor-acceptor (D-A) molecules. β values relevant for hyper-Rayleigh experiments are calculated at 1.064 and 0.830 μm for a complex with such a structure, [5-((4'-dimethylamino)phenyl)ethynyl)-15-((4''-nitrophenyl)ethynyl)-10 ,20-diphenylporphinato]zinc(II), and are 472 x 10-30 and 8152 x 10-30 cm5/esu, respectively. The values are 1 order of magnitude larger than that calculated for any other porphyrin bridged donor-acceptor chromophore studied to date. The considerably enhanced hyperpolarizability arises from the significant excited-state electronic asymmetry manifest in such structures (derived from the strong bridge-mediated D-A coupling enabled by the largely porphyrin-based excited state) and the large bridge-centered oscillator strength in this new class of D-bridge-A molecules. Our analysis of NLO properties (based upon INDO/SCI calculations within the sum over states formalism) shows a sensitivity to the degree of cumulenic character in the ground state. Calculations on structurally related multiporphyrin systems suggest candidate chromophores with further enhanced optical nonlinearities.

Duke Scholars

Author Michael J. Therien Chemistry

Author David N. Beratan Chemistry