Jack R. Tallent

Photochemistry in Dried Polymer Films Incorporating the Deionized Blue Membrane Form of Bacteriorhodopsin

The preparation and photochemical properties of dried deionized blue membrane (dIbR600; lambdamax approximately 600 nm, epsilon approximately 54, 760 cm-1 M-1, f approximately 1.1) in polyvinyl alcohol films are studied. Reversible photoconversion from dIbR600 to the pink membrane (dIbR485; lambdamax approximately 485 nm) is shown to occur in these films under conditions of strong 647-nm laser irradiation. The pink membrane analog, dIbR485, has a molar extinction coefficient of approximately 39,000 cm-1 M-1 (f approximately 1.2). The ratio of pink --> blue and blue --> pink quantum efficiencies is 33 +/- 5. We observe an additional blue-shifted species (dIbR455, lambdamax approximately 455 nm) with a very low oscillator strength (f approximately 0.6, epsilon approximately 26,000 cm-1 M-1). This species is the product of fast thermal decay of dIbR485. Molecular modeling indicates that charge/charge and charge/dipole interactions introduced by the protonation of ASP85 are responsible for lowering the excited-state all-trans --> 9-cis barrier to approximately 6 kcal mol-1 while increasing the corresponding all-trans --> 13-cis barrier to approximately 4 kcal mol-1. Photochemical formation of both 9-cis and 13-cis photoproducts are now competitive, as is observed experimentally. We suggest that dIbR455 may be a 9-cis, 10-s-distorted species that partially divides the chromophore into two localized conjugated segments with a concomitant blue shift and decreased oscillator strength of the lambdamax absorption band.

Effective photochromic nonlinearity of dried blue-membrane bacteriorhodopsin films.

We report the effective nonlinearity for photochromic conversion in a blue-membrane bacteriorhodopsin film hosted in a dry polyvinyl alcohol matrix. The shift in absorption maximum on photoconversion in this film is larger than that of the same material in hydrated form, thus offering a larger modulation of the refractive index. The photoexcited index modulation is stable for several months, which provides for holographic data recording and long-term photochromic data storage. The effective index modulation is experimentally measured and is in good agreement with the theoretical predictions based on the Kramers-Kronig transformation.

Quantum effects, thermal statistics and reliability of nanoscale molecular and semiconductor devices

The reliability of nanoscale molecular and semiconductor devices is analysed in terms of generalized error prediction algorithms. The authors statistical procedures predict the reliability of a device based on the assignment of three independent variables. The first variable, P(1) is the probability of determining the state of the device if only one molecule (or information carrier) is present. The second variable N is the number of molecules (or information carriers) operating to assign the state of the device (that is, the number of quantized entities within the ensemble). The third variable xi lim is the limiting logarithmic reliability factor which is a function of the entire system and the environment in which it must operate. Statistical procedures are also presented which allow one to determine the total system reliability based on the assignment of the desired mean-time-between-failures (DMTBF) and the individual reliabilities of the components. Sample reliability analyses are carried out on three devices to determine the minimum number of molecules N that must be included in the ensemble to achieve an error probability of less than 10-10.

Protein-based volumetric memories

The promise of new architectures and more cost-effective miniaturization has prompted interest in hybrid molecular and semiconductor computers. Nature has already optimized through serendipitous natural selection some molecules for such applications. We examine here the use of the protein bacteriorhodopsin in three-dimensional optical memories. By using a sequential one-photon process, parallel read and write processes can be carried out without disturbing data outside of the irradiated volume. We examine the architecture and the methods currently under study to enhance the relevant photophysical properties of the protein.

CONFORMATIONAL ENERGETICS AND EXCITED STATE LEVEL ORDERING IN 11‐cis RETINAL*

Abstract— Semiempirical molecular orbital theory and semiclassical solvent effect theory are used to analyze the conformational and electronic properties of the 12‐s‐cis and 12‐s‐trans conformers of 11‐cis retinal. The goal is to examine the influence of solvent environment on the equilibrium geometries of these conformers as well as to provide a perspective on the electronic transitions that contribute to the four band systems that are observed in the 200–500 nm region of the optical spectrum. We conclude that the 12‐s‐cis isomer is more stable in vacuum, but that the 12‐s‐trans conformer is preferentially stabilized in both polar and nonpolar solvent environment due to dispersive as well as electrostatic interactions. This observation is in substantial agreement with previous literature results. In contrast, our analysis of the excited state manifold indicates that the spectral features observed in the absorption spectrum are asSociated with a complex set of overlapping transitions. A total of 18 π←π transitions contribute to the four bands, and in some cases, conformation changes the relative contribution of the individual transitions that define the overall band shape. This study provides the first definitive assignments for all four band systems.

Spatial Light Modulators And Optical Associative Memories Based On Bacteriorhodopsin

In this paper we present an overview of current research on the development of spatial light modulators and optical associative memories based on bacteriorhodopsin. The spatial light modulator is a thesholding type and uses oriented bacteriorhodopsin in chemically optimized polymer matrices. The associative memory uses bacteriorhodopsin to store reference holograms and is based on the closed loop autoassociative design of Paek and Psaltis [Opt. Eng. 26, 428-433 (1987)l which includes both feedback and thresholding. We demonstrate that bacteriorhodopsin provides an outstanding photochromic material for use in optically coupled devices of the type investigated here.

Bioelectronics, three-dimensional memories and hybrid computers

The promise of new architectures and more cost-effective miniaturization has prompted interest in hybrid molecular and semiconductor computers. Nature has already optimized some molecules for such applications. We examine here the use of the protein bacteriorhodopsin in associative and three-dimensional memories and the potential for making hybrid computer systems which combine semiconductor and biomolecular components.<<ETX>>

Nonlinear Optical Properties of Bacteriorhodopsin: Assignment of the Third-order Polarizability Based on Two-Photon Absorption Spectroscopy.

The third-order (pi) -electron polarizability, (gamma) (pi), of bacteriorhodopsin in the 0.0 - 1.2 eV optical region is assigned based on an analysis of the experimental two-photon properties of the low-lying singlet state manifold. The following selected values of (gamma) (pi) (units of 10-36 esu) are observed: (gamma) (0;0,0,0) equals 2482 +/- 327; (gamma) (-3(omega) ;(omega) ,(omega) ,(omega) ) equals 2976 +/- 385 ((omega) equals 0.25 eV), 5867 +/- 704 ((omega) = 0.5 eV), 14863 +/- 1614 ((omega) = 0.66 eV), 15817 +/- 2314 ((omega) equals 1.0 eV), 10755 +/- 1733 ((omega) equals 1.17 eV). The third-order polarizability of this protein which contains an all-trans retinyl protonated Schiff base chromophore with six double bonds, is comparable to that observed for much longer chain polyenes (for example, dodecapreno (beta) -carotene, a polyene with 19 double bonds, exhibits a third-order (pi) -electron polarizability at 0.66 eV of 17000 +/- 6000 X 10-36 esu. The authors attribute the enhanced third-order nonlinearity associated with the protein bound chromophore of bacteriorhodopsin to two mutually enhancing origins. First, the chromophore is protonated, and the resultant charge reorganization enhances the polarizability in a fashion that is similar to that known to occur for polaronic and bipolaronic chromophores. It is estimated that protonation generates a five-fold enhancement in (gamma) (pi). Second, the protein bound chromophore exhibits a large change in dipole moment upon excitation into the lowest-lying, strongly-allowed 1B*u+-like state ((Delta) (mu) = 13.5 D). The latter property is responsible for a Type III enhancement of the third-order polarizability, and yields at least a 20-fold increase in (gamma) (pi).

Theoretical analysis of third order polarizability enhancement of disubstituted diphenyl polyenes via oxidative doping

The static field third order polarizability, γxxxx(0;0,0,0), is calculated for an oligomeric series of disubstituted diphenyl polyenes and their bipolarons by using INDO‐PSDCI finite perturbation procedures. Our procedures have the advantage of maintaining a degree of size consistency that is difficult to achieve by using the sum‐over‐states approach. The chain length dependance of γxxxx(0;0,0,0) is calculated to be 21.6N1.9×10−36 esu and 20.1N2.3×10−36 esu for the neutral and bipolaronic species, respectively, where N is the number of carbon atoms in the polyene chain. Although our calculations agree with previous studies that predict that a bipolaron will have an enhanced third order polarizability relative to the corresponding neutral polyene, the length dependance that we observe for both the neutral and bipolaronic species is much smaller than that predicted by previous literature investigations.