Spectral Properties Of Molecules Research Articles

Forgotten Topological and Wiener Indices of Prime Ideal Sum Graph of Zn.

Chemical graph theory is a sub-branch of mathematical chemistry, assuming each atom of a molecule is a vertex and each bond between atoms as an edge. Owing to this theory, it is possible to avoid the difficulties of chemical analysis because many of the chemical properties of molecules can be determined and analyzed via topological indices. Due to these parameters, it is possible to determine the physicochemical properties, biological activities, environmental behaviours and spectral properties of molecules. Nowadays, studies on the zero divisor graph of Z_n via topological indices is a trending field in spectral graph theory. For a commutative ring R with identity, the prime ideal sum graph of R is a graph whose vertices are nonzero proper ideals of R and two distinctvertices I and J are adjacent if and only if I+J is a prime ideal of R. In this study the forgotten topological index and Wiener index of the prime ideal sum graph of Z_n are calculated for n=p^α,pq,p^2 q,p^2 q^2,pqr,p^3 q,p^2 qr,pqrs where p,q,r and s are distinct primes and a Sage math code is developed for designing graph and computing the indices. In the light of this study, it is possible to handle the other topological descriptors for computing and developing new algorithms for next studies and to study some spectrum and graph energies of certain finite rings with respect to PIS-graph easily.

Fluorescence of molecular composites that consist of nematic liquid crystal and merocyanins

Background: Considered merocyanine molecules have donor D and acceptor A moieties connected by polymer chain. The conjugated donor D and acceptor A parts of merocyanine molecules are planar in the ground state. The D-π-A molecular complexes can change their conformations in an excited state due to cis-trans-conformational transitions. The viscosity of the solvent affects conformational changes, photoluminescence (PL) decay and PL lifetime. Therefore the PL of merocyanine molecules strongly depends on medium in excited and ground states. A nematic liquid crystal was utilized as a solvent for merocyanine molecules since it is characterized by long range order, orientates merocyanine molecules along its axis and is sensitive to external electro-magnetic field. The molecules with conjugated donor D and acceptor A parts are promising for molecular electronics (instruments for recording and processing information), optoelectronics (laser technologies) and biological research (fluorescent probes like prominent thioflavin T), since their PL essentially depends on the nature of the environment. Objectives: The main objective of this paper is to investigate and explain impact of liquid crystal medium on considered molecules. Also influence of molecular conformational changes on their spectral properties is considered. Materials and Methods: Two types of merocyanine molecules M-1 and M-2 were investigated. The spectral properties of molecules in different organic solvents such as acetonitrile, toluene, glycerol, and in 4-pentyl-4′-cyanobiphenyl (5CB) liquid crystal were compared. Stationary and time-resolved emission spectra of molecular merocyanine solutions were used to investigate conformational changes of molecules. To determine a lifetime of molecular excited states, a technique of Time Correlated Single Photon Counting with picosecond resolution in time was used. Results: The results indicate that optical properties strongly depend on conformation of conjugated donor-π-acceptor compounds. A relaxation of dye molecules to the ground state is accompanied by conformational changes. The quantum yield and lifetime of PL increase in more viscous solvents. The liquid crystal made conformational changes of considered molecules in ground and excited states. Conclusions: Analysis of the results serves as a basis for constructing a theory that explains properties of D-π-A molecular compounds under optical excitation. The molecular pairs are formed by merocyanine and liquid crystal molecules. The liquid crystal molecule defines conformation of merocyanine molecule in a pair. Moreover, both types of merocyanine molecules in liquid crystal have the same conformation. This hypothesis explains similarities of optical properties of M-1 and M-2 molecules in liquid crystal.

Photoelectrochemistry of molecules in zeolites and clays

While zeolites (aluminosilicates) with supercages and window openings of molecular dimensions encapsulate molecules inside the supercages based on their size- and shape-selective properties, clays exchange cations across their aluminosilicate layers. The important aspects of the photochemistry of molecules in zeolite and clay are reduced mobility of the trapped molecules (compared with solution mobility), the stabilization of positively charged molecules and an increase in the selectivity of reactions. The present study is concerned with the absorption and emission spectral properties of tris(2,2′-bipyridine)ruthenium(II) in zeolite and clay. The nature of zeolite or clay does not appear to influence the spectral properties of molecules in these organized assemblies. The ruthenium(II) encapsulated into the supercages of zeolite-Y is electroinactive and cannot be used for photoelectrocatalytic applications. However, the sensitizer molecules incorporated into clay coated electrodes are electroactive and are capable of carrying out multi-step one-electron transfer photoelectrocatalytic reduction of oxygen to hydrogen peroxide.

“Proximity effects” in radiative transitions: a model study of the role of vibronic coupling and static crystal field interactions

We report the results of a model study of the influence of vibronic coupling involving non-totally symmetric vibrations and static crystal field interactions on the spectral properties of molecules with close-lying excited electronic states. The presented results suggests that “proximity effects” brought about by solvent perturbation arise from two sources: (i) alterations in the energy separation between vibronically coupled electronic states and (ii) crystal field mixing of the isolated molecular electronic states. It is shown that crystal field mixing leads to the breakdown of the vibronic coupling scheme for non-totally symmetric vibrations in isolated molecules. This breakdown is shown to have a very pronounced effect on the spectral properties of molecules with close-lying excited electronic states. The effect of environmental perturbations on excited state frequencies, the breakdown of symmetry and polarization selection rules, and vibrational intensity distributions is discussed.