Inorganic aromatic compounds - theoretical study of structure, bonding, spectral and optical properties

Master's Thesis/Inorganic Chemistry

Abstract

Regarding the application of nonlinear optical properties (NLO) in technologies such as lasers, telecommunications, photovoltaic cells, information processing and holography, and the mineral diversity of these materials, we started a research in this field And we focused on dyes with borazine.

Our main goal in this research is to achieve the use of borazine part to design NLO molecular dyes and to obtain structure-function relationships within this system. We studied stability, dipole moment, polarization, frontal orbital, structure, most intense electron jump and superpolarizability. Also, good linear relationships were obtained between some of the studied properties.

The study was conducted using the density function theory (DFT) calculation method on the nonlinear optical properties of borazine-containing dyes.

We studied two isomers, B and N. All studied molecules are non-planar.

Theoretical studies showed that the acceptor substitutions increase the values ??of the first superpolarizability in the N isomer compared to the B isomer, although these values ??are lower in the N isomer than the B isomer despite the donor substitutions.

Key words: nonlinear optical materials, dyes with borazine

Chapter One

1-1 Aromatic cyclic compounds

Benzene is the first example [1] of a molecule that has remarkable physical properties due to the lack of electrons. p is Historically, chemists have done a lot of research on other molecules similar to benzene. Borazine (B3N3H6), boroxine (B3O3H3) and bortine (B3S3H3) are examples of these compounds. These compounds have a structure similar to benzene and the topology of their molecular orbitals is similar. The question of whether their pi electrons are unstable like benzene (resonance between Kekule structures) is not so clear.

1-2 Aromatics

Since the introduction of aromatics by August Kekule in 1865, it has continuously conquered[2]new territories[3] in chemistry. Initially, aromaticity was extended to the following organic compounds:

planar conjugated monocyclic hydrocarbons and their ions having 4n+2 p electrons.

polycyclic conjugated hydrocarbons - benzoic hydrocarbons made of fused benzene rings.

Hydrocarbons Polycyclic conjugated carboxylic based on non-benzoic systems such as azulene and other conjugated hydrocarbons with four, five, seven and eight membered rings.

Compounds with metal atoms can also be aromatic. In 1979, Thorn and Hoffmann predicted that some hypothetical metallocycles should exhibit labile bond character and some aromatic character. In the following years, about 25 metallobenzenes were isolated and identified. The first example of a stable and separable metallobenzene was isobenzene, which was reported in 1982. A large family of metallobenzenes (iridabenzenes) were also prepared later, while a series of dimetallobenzenes with two metal atoms in the benzene ring were reported. The first organic metal compound with an aromatic ring composed of metal atoms was prepared in 1995. Na2[(Mes2C6H3)Ga]3 which contains a triangular aromatic ring with two p electrons. The first aromatic organometallic compound consisting of four gallium atoms had a square structure K2[Ga4(C6H3-2,6-Trip2)2].

Aromatic ring flow is an effect that is observed in aromatic molecules such as benzene, naphthalene.If a magnetic field is applied perpendicular to the plane of the aromatic system, a ring current is induced in the p-electrons of the aromatic ring. This is a direct consequence of Ampere's law because the included electrons are free to circulate instead of being fixed in bonds as in non-aromatic molecules, so they respond strongly to a magnetic field.

Aromatic ring currents are associated with NMR spectroscopy. So they affect the chemical shifts of 13C, 1H nuclei in aromatic rings and other organic and inorganic molecules. This effect makes it possible to detect nuclear environments and thus has a wide application in determining the molecular structure. In benzene, aromatic protons are depolarized because the induced magnetic field has the same direction as the external field.

So a diamagnetic or diaprotic loop current is associated with aromaticity, and a paratropic loop current is a sign of antiaromaticity. A similar effect is observed in three-dimensional fullerenes and it is called sphere flow.

Several attempts have been made to quantitatively express aromaticity:

1-4 Quantitative Aromaticity Expression

1-4-1 nucleus-independent chemical shift [1]:

The nucleus-independent chemical shift parameter is used to describe aromaticity from a magnetic point of view. This index is determined by P.v.R. Schleyer and his colleagues were invented based on magnetic coatings and calculated with simple methods. Even now, calculations are done with advanced initial methods (25). This index is used by calculating the negative absolute magnetic envelope of the spirit atom [2] at the center of the ring (26) or other desired points (27). The value of NICS shown as NICS (1.0) means its calculation at a distance of ?1 above the ring and is expected to determine the details of the electronic structure of p. Because the value of NICS(0.0) in the plane is affected by local contributions of s bonds and lone pairs (28). Rings with negative NICS are aromatic, rings with NICS close to zero are non-aromatic, and rings with positive NICS are anti-aromatic.

Another indicator is the "out-of-plane" component of the NICS tensor, which is calculated at a distance of ?1 above the center of the ring and is denoted by NICS(1.0)zz, which is a good measure for ring p-system characteristics (29). Since a magnetic field is applied perpendicular to the plane of the ring, this value is more directly related to the induced current densities in the ring system of the molecule. As a result, NICSzz calculated at distances away from the ring center (where NICSzz is influenced by contributions from the p system) characterizes NICS well(30).

It has been proven that for borazine derivatives, NICS(2.0)zz is a good measure of aromaticity(31).

Scrutinized values ??[3] NICS with software deMonNMR are calculated (32). Accordingly, NICS(total) is divided into shares of p bonds, NICS(p), s bonds, NICS(s), and other contributions (bonds with hydrogen, lone pairs in the plane of the molecule, brain orbitals). rtl;">

Due to their potential application in technologies such as lasers, telecommunications, photovoltaic cells, organic light emitting diodes, and semiconductor layers in field-effect transistors, information processing and holography and a variety of inorganic these materials We report here on a systematic computational investigation of the NLO properties of borazine-based chromophores. The main purpose here is to assess the use of borazine moieties for the design of molecular NLO chromophores and to obtain insight into the structure-function relationships of these systems. We studied the effects of various donor and acceptor substituents (H, F, Cl, Br, Me, NH2, OH, COOH, CHO, CN, NO2) on the stability, dipole moment, polarizability, frontier orbitals, structure, the most intense electronic transition, and hyperpolarizabilities. Also, we obtained good linear relationships between some of the studied properties