Brian Wesley Williams

Further Solvatochromic, Thermochromic, and Theoretical Studies on Nile Red

Experimental steady-state solvatochromic and thermochromic studies of Nile Red absorption and emission in nine dipolar solvents are reported, as well as theoretical modeling results concerning the ground and excited states of Nile Red in solution. Solvatochromic absorption and emission data analyzed according to conventional methods yield ground- and excited-state dipole moments of 8.9 ± 0.5 and 14.4 ± 0.5 D. Application of this conventional model to thermochromic shift data gave dipole moments of 8.4 ± 1.0 and 13.4 ± 1.0 D. The thermochromic data were also analyzed using a novel solute monopole–solvent dipole model; this model did not appear to reproduce trends in the thermochromic shift data as well as the conventional model. Results of semiempirical ZINDO/S calculations on Nile Red combined with an Onsager model for solvation were also used to examine the energetics of the excited states of Nile Red in solution. These calculations suggest the presence of a TICT state in Nile Red comparable in energy to an emitting excited state at high solvent polarity. Conventional models for solvatochromic and thermochromic response, however, appear to explain the experimental results independently of any emission from this TICT state in the present solvents.

IMPLICIT POTENTIALS ASSOCIATED WITH JACOBI POLYNOMIALS: SOME NOVEL ASPECTS

Abstract The Schrodinger equation is solved for a potential V ( g ( r )) with an implicitly defined g ( r ) function. Generally, it resembles certain Poschl-Teller potentials, up to isospectrality in a particular case. Together with a closely related implicit potential, it also offers a good example demonstrating certain unusual characteristics of attractive singular potentials.

A simple method for generating exactly solvable quantum mechanical potentials

A simple transformation method permitting the generation of exactly solvable quantum mechanical potentials from special functions solving second-order differential equations is reviewed. This method is applied to Gegenbauer polynomials to generate an attractive radial potential. The relationship of this method to the determination of supersymmetric quantum mechanical superpotentials is discussed, and the superpotential for the radial potential is also derived.

A second class of solvable potentials related to the Jacobi polynomials

Levai (1991) has used a simple method for generating solvable wave equations to construct potentials whose solutions include as factors Jacobi polynomials of functions g(x) which solve specific differential equations. Application of this method to a previously unconsidered differential equation involving Jacobi polynomials results in a new class of solvable potentials missing from earlier compilations. An interesting property of these new potentials is that when two of their defining parameters are fixed, they all possess the same energy eigenvalue spectrum independent of any change in a third parameter, leading to an indefinite number of different potentials with the same energies.

Fluorescence in Membranes

The study of membranes poses a unique challenge in science due to their complex and fluid nature. Until recently, the majority of experiments was conducted in either fixed samples or on population levels that did not give insight into individual events. However, recent advances in fluorescence microscopy techniques have allowed scientists to visualize microscopic perturbations of individual vesicles and have allowed the study of membrane dynamics at higher spatiotemporal resolution than before.

An asymmetric "implicit" potential on the real line

An exactly solvable, two-parameter implicit quantum mechanical potential is derived and characterized. With a change of variable, this potential is shown to belong to the Natanzon class, and for at least one value of the potential parameters, an explicit, rather than implicit, potential results.

Synthesis and characterization of a solvatochromic, lipophilic fluorescent oxazone: 1-Pentyl-7-dimethylamino-3H-phenoxazine-3-one.

Olivetol and 4-nitroso-N,N-dimethylaniline were combined under reflux in acetic acid to produce 1-pentyl-7-dimethylamino-3H-phenoxazine-3-one (1-PDMPO). The fluorescent behavior of the purified compound in a variety of solutions and samples was investigated. Excitation and emission spectra in pure solvents and mixtures of solvents demonstrate solvatochromism, indicating that the fluorescence response of this compound is affected by its environment. Nonpolar, aprotic solvents as well as protic, polar solvents diminish fluorescent emission in the spectral regions examined, and trends in the fluorescence decary lifetimes measured in five pure solvents are consistent with these intensity changes. The anisotropy excitation spectrum taken in glycerol for 1-PDMPO at −15°C appears to be consistent with the presence of a single electronic state upon excitation, with anisotropy values approaching 0.35 over 400–600 nm. Fluorescence emission is also diminished at low acid concentrations in methanol, with smaller decreases observed in more highly concentrated basic solutions. Emission peaks in aqueous sodium dodecyl sulfate solutions, extruded egg phosphatidylcholine vesicles, and fatty acid free bovine serum albumin suspensions all lie above 600 nm, with emission in the albumin suspension displaying a broad shoulder extending to 800 nm. The fluorescent properties of this compound suggest that it or structural homologues may have utility as fluorescent biological probes.

Characterization of a Solvatochromic Fluorophore: 1-(2,2-Dicyanovinyo)-2,5-Dimethoxybenzene (DCN-2,5-DMOB)

Absorption spectra and steady-state fluorescence emission spectra for l-(2,2-dicyanovinyl)-2,5-dimethoxybenzene in five solvents were determined. Although the absorption spectra demonstrate little solvatochromism, emission peaks show a red shift of roughly 90 nm between cyclohexane and methanol or acetonitrile, which appears to indicate charge transfer associated with a relaxed, as opposed to a vertical, excited state. Semiempirical gas phase AM1 calculations on this compound and the related unsubstituted 2,2-dicyanovinyl benzene indicate a dihedral twist of roughly 35° between the phenyl and the dicyanovinyl planes for both molecules in their ground states, as well as substantial polarity associated with the ground states of these compounds.

2-(1,2,3,4-Tetra-hydro-phenanthren-1-yl-idene)malononitrile.

In the title complex, C17H12N2, the non-aromatic six-membered ring adopts an envelope conformation. The dihedral angle between the eight-membered plane containing the malononitrile group and the aromatic system is 25.88 (4)°. The distance from the central C atom of the malononitrile group to the centroid of the n-glide-related distal aromatic ring is 3.66 Å, suggesting π–π interactions.

The M&M Superposition Principle.

A macroscopic physical system for demonstrating the relationships of quantum mechanical operators, eigenfunctions, expectation values, and superposition of delectable wave functions is described. Small candies or similar objects with a variety of values of physical properties serve as surrogates for abstract quantum wave functions.