Solvent Effects on the Resonance Raman and Hyper-Raman Spectra and First Hyperpolarizability of N,N-Dipropyl-p-nitroaniline

Linear absorption spectra, resonance Raman spectra and excitation profiles, and two-photon-resonant hyper-Rayleigh and hyper-Raman scattering hyperpolarizability profiles are reported for the push-pull chromophore N,N-dipropyl-p-nitroaniline in seven solvents spanning a wide range of polarities. The absorption spectral maximum red shifts by about 2700 cm(-1), and the symmetric -NO2 stretch shifts to lower frequencies by about 11 cm(-1) from hexane to acetonitrile, indicative of significant solvent effects on both the ground and excited electronic states. The intensity patterns in the resonance Raman and hyper-Raman spectra are similar and show only a small solvent dependence except in acetonitrile, where both the Raman and hyper-Raman intensities are considerably reduced. Quantitative modeling of all four spectroscopic observables in all seven solvents reveals that the origin of this effect is an increased solvent-induced homogeneous broadening in acetonitrile. The linear absorption oscillator strength is nearly solvent-independent, and the peak resonant hyperpolarizability, beta(-2omega;omega,omega), varies by only about 15% across the wide range of solvents examined. These results suggest that the resonant two-photon absorption cross sections in this chromophore should exhibit only a weak solvent dependence.

Solvent effects on resonant first hyperpolarizabilities and Raman and hyper-Raman spectra of DANS and a water-soluble analog

The two-photon-resonant first hyperpolarizabilities associated with hyper-Rayleigh and hyper-Raman scattering are reported for 4-dimethylamino-4-nitrostilbene in 1,4-dioxane, dichloromethane, acetonitrile, and methanol, and for an ionic analog, 4-N,N-bis(6-(N,N,N-trimethylammonium)-hexyl)amino-4-nitrostilbene dibromide in methanol and water. Resonance Raman and hyper-Raman excitation profiles are also measured and modeled. The resonance Raman and hyper-Raman spectra show very similar relative intensities which do not vary much as the excitation frequency is tuned across the lowest-energy strong linear absorption band, suggesting that a single resonant electronic state dominates the one- and two-photon absorptions in this region. The absorption, resonance Raman, and hyper-Raman profiles can be simulated reasonably well with a common set of parameters. The peak resonant (absolute value of beta)2, measured by hyper-Rayleigh scattering, varies by about 50% over the range of solvents examined and shows a weak correlation with the linear absorption maximum, with the redder-absorbing systems exhibiting larger peak hyperpolarizabilities. The experimental hyper-Rayleigh intensities are higher than those calculated, possibly reflecting contributions from nonresonant electronic states.

Chiral 1,2- and 1,3-Diol-Functionalized Chromophores as Lego Building Blocks for Coupled Structures

Chiral nitroanilines containing 1,2- or 1,3-diol functionalities have been synthesized by nucleophilic aromatic substitution of fluoronitroanilines with 1-aminopropane-2,3-diols and 2-aminopropane-1,3-diol in the melt. X-ray structure analyses confirm retention of the configuration of the chiral center. The novel chromophores are suitable to link reversibly to various substituted arylboronic acids which allows the construction of new solvatochromic sensor molecules suitable to response to solvent and anion coordination by fluoride. The solvatochromism of the new compounds has been studied using the Kamlet-Taft LSE relationship.

Characterization of small unilamellar vesicles using solvatochromic π* indicators and particle sizing

A suite of small unilamellar vesicles (SUVs) composed of mixtures of phospholipids and cholesterol (CH) or the synthetic surfactant dihexadecyl phosphate (DHP) and cholesterol was investigated using a homologous series of solvatochromic pi* indicators coupled with size exclusion methods and photon correlation spectroscopy (PCS). The solvatochromic method, which is based on the measurement of solvent-dependent shifts in lambda(max) from UV-Vis spectra of solubilized indicators, was used to quantify the dipolarity and polarizability (pi*) of probe solvation environments. The partitioning of the series of individual di-n-alkyl-p-nitroaniline (DNAP) pi* indicators in PG(24)PC(46)Chol(30) and DHP(70)Chol(30) SUVs was examined as a function of the head group structure as well as the method of dye-vesicle preparation. Solubilization of the larger more hydrophobic probes in the bilayer portion of PG(24)PC(46)Chol(30) SUVs was aided through physical entrapment. Such physical methods were not needed for the smaller indicators or for the range of indicators in the DHP(70)Chol(30) dispersions. Extrusion and size-exclusion chromatographic methodologies for the preparation of physically entrapped dopants in SUVs of fixed size range demonstrated that the larger (longer alkyl chain) dopants in the series resided in PG(24)PC(46)Chol(30) liposomes with a wider range of sizes, while the smaller more polar solutes tended to be entrapped in smaller vesicles with a narrower size range.