Glenn P. Bartholomew

Resonance Raman, hyper-Raman, and hyper-Rayleigh depolarization ratios and symmetry breaking in solution

The depolarization ratios in resonance Raman, resonance hyper-Raman and resonance hyper-Rayleigh scattering have been measured for two octupolar conjugated organic chromophores that possess nominal threefold symmetry, crystal violet (CV) and 1,3,5-tris[4-[(1E)-2-(4-nitrophenyl)-ethenyl]phenyl]benzene (TPB(PV)1(NO2)). For comparison, the same quantities are measured for two dipolar donor–acceptor substituted conjugated molecules. The dipolar molecules both exhibit depolarization ratios of for resonance Raman and ρ = 1/5 for hyper-Rayleigh and hyper-Raman, consistent with the polarizability and the hyperpolarizability tensors having a single non-zero element. The resonance hyper-Rayleigh scattering from both of the octupolar molecules exhibits a depolarization ratio close to the value of 2/3 expected for D3h or D3 symmetry, but the resonance Raman and resonance hyper-Raman depolarization ratios deviate significantly from the values expected for those symmetries. In TPB(PV)1(NO2), the depolarization ratios indicate that the resonant vibrational polarizability and hyperpolarizability tensors are dominated by a single diagonal term, suggesting that each of the three conjugated chains acts as a nearly independent chromophore. The results for CV are more complicated and suggest partial but incomplete delocalization of the electronic and/or vibrational excitations among the three nominally equivalent chromophores.

Modification of nonlinear optical dyes for dye sensitized solar cells: a new use for a familiar acceptor

The chemistry of electron deficient π-acceptors offers unique challenges in the rational design and synthesis of organic dyes for use in solar cells. We have synthesized 2-cyano-2-(3-cyano-4-((E)-4-(dibutylamino)styryl)-5,5-dimethylfuran-2(5H)-ylidene)ethanoic acid (2), a dye containing an carboxylated version of the strongly electron withdrawing TCF group by way of stepwise synthesis and isolation of 2,5-dihydro-2-imino-4,5,5-trimethylfuran-3-carbonitrile (5), previously only available as an intermediate available via microwave chemistry. We use this dye to sensitize nanocrystalline TiO2 in order to examine its efficacy in dye-sensitized solar cells. Crystal structures of an intermediate and the final dye are presented and the isomerization about the terminal alkene is discussed in addition to preliminary solar cell data.

Raman and site-selective fluorescence spectra of model compounds for interchain interactions in poly(phenylenevinylene)

Abstract Nonresonant Raman spectra and site-selective fluorescence spectra (polyethylene matrix, 1.5 K) are reported for 1,4-distyrylbenzene, its tert -butyl and paracyclophane substituted derivatives, and the paracyclophane derivative bearing two distyrylbenzene chains in a pseudo- para orientation, a simple model for the interchain interactions in poly(phenylene-vinylene) films. The first three compounds show pronounced fluorescence line-narrowing when excited near the red edge of their absorption spectra. The bichromophoric compound exhibits no narrowing although its Raman spectrum, room-temperature fluorescence spectrum, and lifetime are similar to those of the other three molecules. This may reflect increased low-frequency Franck–Condon activity in the electronically delocalized bichromophoric system.