Design, synthesis, and optoelectronic properties of strongly coupled porphyrin based donor -acceptor systems

This thesis focuses on the design, synthesis, and spectroscopy of several classes of strongly coupled porphyrin-based chromophores and their nonlinear optical (NLO) properties. Previous work in our laboratory has shown that the nonlinear optical properties of our prototypical NLO chromophore, [5-(4 ′-dimethylaminophenyl)ethynyl)-15-(4″-nitrophenyl)ethynyl)-10,20-diphenylporphinato]zinc(II), whose nonlinear optical coefficient, β(0), as measured by Hyper-Rayleigh light scattering measurements (HRS), was reported as one of the highest values for organic chromophores to date. Initial work focused on the design and synthesis of amphiphilic porphyrin based chromophores to fabricate ordered films based on the Langmuir-Blodgett (LB) technique. These results show that multi-layer films were prepared and that a measurable nonlinear optical susceptibility was observed. Moreover, these studies indicate that interleaving NLO-inactive polymer layers between the NLO-active porphyrin layers generated films with greater bulk order and hence, a greater nonlinear optical susceptibility. In an effort to examine the conjugation length dependence on the nonlinear optical coefficient, a new class of porphyrins in which an intervening ethynyl moiety connects (porphinato)zinc(II) units and aryl groups at the porphyrin meso 5- and 15-positions have been synthesized. Furthermore, design elements to maintain and enhance solubility were implemented whose electronic properties minimally perturb the overall electronic structure of the target systems. Electronic absorption spectroscopy, mass spectrometry, nuclear magnetic resonance (NMR), and steady state fluorescence were utilized to characterize and investigate various [5,15-bis[(aryl)ethynyl]-10,20-di(2′ ,6′-bis(3,3-dimethyl-1-butyloxy)phenylporphinato]zinc(II) compounds as well as the x-ray structural determination of a number of chromophores based on this structural motif. The data are indicative of (i) removal of the steric barrier between the porphyrin and arylethynyl-phenyl aromatic systems, (ii) enhanced π-conjugative interactions, and (iii) enhanced second-order nonlinear optical activity with increasing conjugated (porphinato)zinc(II) units. The larger molecular first-order hyperpolarizabilities, β, determined by electro-optical absorption spectroscopy (EOAM) and coupled with Hyper-Raleigh scattering (HRS) and electric field induced second-harmonic generation (EFISH) measurements suggest that this chromophoric motif and related structures may find utility in the development of electro-optic devices as well as materials for efficient frequency doubling