Photoisomerization Of Molecules Research Articles

Mathematical modeling of morphological changes in photochromic crystals by catastrophe theory

Photochromic diarylethene is known to exhibit reversible photoisomerization under irradiation with ultraviolet (UV) and visible light. Besides reversible optical properties upon light irradiation, a variety of discontinuous morphological changes of the crystals are reported in the literature, such as sudden crystal bending, cracking, and photosalient effects, which are caused simply by UV and visible light irradiation. These morphological phenomena with discontinuities are micro-scale changes caused by photoisomerization of molecules at the nanoscale and lead to the realization of important functions for optical devices. However, the theoretical models behind these phenomena are not well understood. In this paper, we construct a mathematical model that can treat diverse phenomena in a unified model by using swallow-tail catastrophe, a higher-order catastrophe than cusp catastrophe, from the seven elementary catastrophes that can describe discontinuities in the phenomena. By introducing hyperbolic operating curves in the model, the intrinsic properties of the photochromic crystals are represented. The induced morphogenesis, such as bending, cracking, and photosalient effects, are systematically classified by the proposed catastrophe model, which even implies the possibility of unexplored operating conditions of the crystals and explains known phenomena. The proposed catastrophe-theory-based modeling provides a foundation for understanding and discovering the versatile morphogenesis in photochromic crystals. Furthermore, the proposed approach provides a basis for understanding and discovering various morphological changes in photochromic crystals and similar systems.

Ultrafast isomerization-induced cooperative motions to higher molecular orientation in smectic liquid-crystalline azobenzene molecules

The photoisomerization of molecules is widely used to control the structure of soft matter in both natural and synthetic systems. However, the structural dynamics of the molecules during isomerization and their subsequent response are difficult to elucidate due to their complex and ultrafast nature. Herein, we describe the ultrafast formation of higher-orientation of liquid-crystalline (LC) azobenzene molecules via linearly polarized ultraviolet light (UV) using ultrafast time-resolved electron diffraction. The ultrafast orientation is caused by the trans-to-cis isomerization of the azobenzene molecules. Our observations are consistent with simplified molecular dynamics calculations that revealed that the molecules are aligned with the laser polarization axis by their cooperative motion after photoisomerization. This insight advances the fundamental chemistry of photoresponsive molecules in soft matter as well as their ultrafast photomechanical applications.

Mathematical modeling of photoisomerization with intramolecular proton transfer

A system of equations describing time changes in the matrix elements of the density operator of a seven-level model of a molecule interacting with a light pulse taking into account spontaneous (including collective) decays of molecule excited states is suggested. Model parameters were selected to allow us to perform modeling of the photoisomerization of a molecule with two isomeric states with different stable proton positions on an intramolecular H-bond by numerically solving the suggested system of equations for density operator matrix elements. An analysis of the characteristic time dependences of the population of states of the model under consideration showed that proton phototransfer in the collective decay of various isomeric states of a molecule in an excited electronic state can be one of effective mechanisms of the photoisomerization of molecules whose structure is described by the model.

Mathematical simulation of phototransfer of the proton of a hydrogen bond under irradiation of a molecule by two light pulses

The time-dependences of the populations of molecular states are determined by the numerical solution of a set of equations for the matrix elements of a density operator for the five-level model of a molecule with different values of parameters of two nonoverlapping in time irradiation pulses and of the constants governing the rates of induced radiative transitions of the molecule, as well as the radiative and nonradiative decays of molecular states. It is proposed to use the results obtained as reference points in interpreting experimental data on the spectro-temporal characteristics of secondary emission upon photoisomerization of molecules with an intramolecular hydrogen bond under irradiation by two light pulses and in determining the mechanism of phototransfer of the hydrogen-bond proton occurring in this process.

Ultrafast dynamics of neutral, ultracold plasmas

The ultrafast dynamics of a neutral, ultracold plasma following an energy landscape shift is studied theoretically and with simulation. To lowest order in time, the inertial dynamics on the new landscape can be characterized by the initial-state plasma microfield, which, for the randomly ordered case of an ultracold neutral plasma, is dominated by nearest-neighbor interactions. Formation of the pair correlation function arises after ballistic overshoot, which leads to oscillations in the effective temperature. Connections are made to similar properties of clusters, photoisomerization of molecules, and nonthermal melting in solids.

Theory of photoisomerization of impurity molecules in solids

In this paper we have presented the density matrix method to derive the master equations for describing the photoisomerization of molecules in solids that take into account the interplay of optical absorption, vibrational relaxation, and molecular isomerization. We have also calculated the isomerization rate constant induced by anharmonic coupling and Coriolis coupling, which is applicable to the whole temperature range from 0 K to the melting temperature of solids. We have shown that the mode selectivity of the photoisomerization of molecules in solids can be interpreted by using the derived master equations.

Selective action of laser radiation on matter

The review deals with the problem of selective interaction of laser radiation with atoms and molecules. Objects of selective interaction (chemical elements and compounds, isotopes, molecular bonds, etc.) are considered first. Next, possible elementary selective processes (photoionization of atoms and molecules, photodissociation and photoisomerization of molecules, photodeflection of particles, photochemical reactivity, etc.) are discussed and the available techniques are classified into photophysical and photochemical methods, atomic and molecular methods, and so on. The review is concerned mainly with the photophysical and photochemical methods of selective interaction in the specific case of laser isotope separation. The last sections of the review deal with other applications which are in the course of development, such as preparation of pure substances, selective laser biochemistry, selective detection of nuclei, atoms, and molecules, and spatial localization of molecular bonds.