369 research outputs found
Studies on optimizing potential energy functions for maximal intrinsic hyperpolarizability
We use numerical optimization to study the properties of (1) the class of
one-dimensional potential energy functions and (2) systems of point charges in
two-dimensions that yield the largest hyperpolarizabilities, which we find to
be within 30% of the fundamental limit. We investigate the character of the
potential energy functions and resulting wavefunctions and find that a broad
range of potentials yield the same intrinsic hyperpolarizability ceiling of
0.709.Comment: 9 pages, 9 figure
Maximizing the hyperpolarizability of one-dimensional systems
Previous studies have used numerical methods to optimize the
hyperpolarizability of a one-dimensional quantum system. These studies were
used to suggest properties of one-dimensional organic molecules, such as the
degree of modulation of conjugation, that could potentially be adjusted to
improve the nonlinear-optical response. However, there were no conditions set
on the optimized potential energy function to ensure that the resulting
energies were consistent with what is observed in real molecules. Furthermore,
the system was placed into a one-dimensional box with infinite walls, forcing
the wavefunctions to vanish at the ends of the molecule. In the present work,
the walls are separated by a distance much larger than the molecule's length;
and, the variations of the potential energy function are restricted to levels
that are more typical of a real molecule. In addition to being a more
physically-reasonable model, our present approach better approximates the bound
states and approximates the continuum states - which are usually ignored. We
find that the same universal properties continue to be important for optimizing
the nonlinear-optical response, though the details of the wavefunctions differ
from previous result.Comment: 10 pages, 5 figure
The effect of extreme confinement on the nonlinear-optical response of quantum wires
This work focuses on understanding the nonlinear-optical response of a 1-D
quantum wire embedded in 2-D space when quantum-size effects in the transverse
direction are minimized using an extremely weighted delta function potential.
Our aim is to establish the fundamental basis for understanding the effect of
geometry on the nonlinear-optical response of quantum loops that are formed
into a network of quantum wires. Using the concept of leaky quantum wires, it
is shown that in the limit of full confinement, the sum rules are obeyed when
the transverse infinite-energy continuum states are included. While the
continuum states associated with the transverse wavefunction do not contribute
to the nonlinear optical response, they are essential to preserving the
validity of the sum rules. This work is a building block for future studies of
nonlinear-optical enhancement of quantum graphs (which include loops and bent
wires) based on their geometry. These properties are important in quantum
mechanical modeling of any response function of quantum-confined systems,
including the nonlinear-optical response of any system in which there is
confinement in at leat one dimension, such as nanowires, which provide
confinement in two dimensions
Experimental verification of a self-consistent theory of the first-, second-, and third-order (non)linear optical response
We show that a combination of linear absorption spectroscopy, hyper-Rayleigh
scattering, and a theoretical analysis using sum rules to reduce the size of
the parameter space leads to a prediction of the two-photon absorption
cross-section of the dye AF455 that agrees with two-photon absorption
spectroscopy. Our procedure, which demands self-consistency between several
measurement techniques and does not use adjustable parameters, provides a means
for determining transition moments between the dominant excited states based
strictly on experimental characterization. This is made possible by our new
approach that uses sum rules and molecular symmetry to rigorously reduce the
number of required physical quantities.Comment: 10 pages, 9 figure
Site-specific N-linked glycosylation analysis of human carcinoembryonic antigen by sheathless capillary electrophoresis-tandem mass spectrometry
With 28 potential N-glycosylation sites, human carcinoembryonic antigen (CEA) bears an extreme amount of N-linked glycosylation, and approximately 60% of its molecular mass can be attributed to its carbohydrates. CEA is often overexpressed and released by many solid tumors, including colorectal carcinomas. CEA displays an impressive heterogeneity and variability in sugar content, however site-specific distribution of carbohydrate structures has not been reported so far. The present study investigated CEA samples purified from human colon carcinoma and human liver metastases and enabled the characterization of 21 out of 28 potential N-glycosylation sites with respect to their occupancy. The coverage was achieved by a multi-enzymatic digestion approach with specific enzymes, such as trypsin, endoproteinase Glu-C, and the non-specific enzyme, pronase, followed by analysis using sheathless CE-MS/MS. In total, 893 different N-glycopeptides and 128 unique N-glycan compositions were identified. Overall, a great heterogeneity was found both within (micro) and in between (macro) individual N-glycosylation sites. Moreover, notable differences were found on certain N-glycosylation sites between primary adenocarcinoma and metastatic tumor in regard to branching, bisection, sialylation and fucosylation. Those features, if further investigated in a targeted manner, may pave the way towards improved diagnostics and monitoring of colorectal cancer progression and recurrence. Raw mass spectrometric data and Skyline processed data files that support the findings of this study are available in the MassIVE repository with the identifier MSV000086774 [https://doi.org/doi:10.25345/C5Z50X]
Diquat Derivatives: Highly Active, Two-Dimensional Nonlinear Optical Chromophores with Potential Redox Switchability
In this article, we present a detailed study of structureâactivity relationships in diquaternized 2,2â˛-bipyridyl (diquat) derivatives. Sixteen new chromophores have been synthesized, with variations in the amino electron donor substituents, Ď-conjugated bridge, and alkyl diquaternizing unit. Our aim is to combine very large, two-dimensional (2D) quadratic nonlinear optical (NLO) responses with reversible redox chemistry. The chromophores have been characterized as their PF_6^â salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Their visible absorption spectra are dominated by intense Ď â Ď^* intramolecular charge-transfer (ICT) bands, and all show two reversible diquat-based reductions. First hyperpolarizabilities β have been measured by using hyper-Rayleigh scattering with an 800 nm laser, and Stark spectroscopy of the ICT bands affords estimated static first hyperpolarizabilities β_0. The directly and indirectly derived β values are large and increase with the extent of Ď-conjugation and electron donor strength. Extending the quaternizing alkyl linkage always increases the ICT energy and decreases the E_(1/2) values for diquat reduction, but a compensating increase in the ICT intensity prevents significant decreases in Stark-based β_0 responses. Nine single-crystal X-ray structures have also been obtained. Time-dependent density functional theory clarifies the molecular electronic/optical properties, and finite field calculations agree with polarized HRS data in that the NLO responses of the disubstituted species are dominated by âoff-diagonalâ β_(zyy) components. The most significant findings of these studies are: (i) β_0 values as much as 6 times that of the chromophore in the technologically important material (E)-4â˛-(dimethylamino)-N-methyl-4-stilbazolium tosylate; (ii) reversible electrochemistry that offers potential for redox-switching of optical properties over multiple states; (iii) strongly 2D NLO responses that may be exploited for novel practical applications; (iv) a new polar material, suitable for bulk NLO behavior
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