Determination of optical properties of pentacoordinated silicon complexes using DFT method

Relevance
Aims and objectives of the study
Aim - To define the optical properties of pentacoordinated silicon complexes using DFT method.
Objectives - To conduct quantum chemical calculation using DFT method; to investigate of the optical properties of the complex Si(pincer)2 ; to determine the charge dependence of the Si complex(ttpy)2 from its electrochromic response; to compare the obtained results with known experimental data, which were got by American scientists.
In recent years, there has been a steady interest in the development of new materials for organic electronic devices. Accordingly, the study of electron transfer processes in organic molecules and coordination complexes with organic ligands meets the modern needs of microelectronics development in Kazakhstan.

Theoretical significance
Practical significance
The research uses a method DFT that allows to get more reliable data.
The results of the research show that silicon pentacoordination complexes represent a promising new class of metallochelates for organic electronic devices in Kazakhstan. That means, they can be used as candidates for transporting charge and/or electroluminescent materials in organic electronic devices.

The object and subject of the study
Chemical structure of the pentacoordinate complex Si[(ttpy)2]+n
Chemical structure of the pentacoordinate complex Si[(pincer)2]0
Object - Pentacoordinated silicon complexes.
Subject - A study of optical properties and quantum-chemical calculations of silicon pentacoordinated complexes with ligands by the DFT method.

Optimised structure of Si(pincer)2 molecule by the B3LYP method
Theoretical modelling of the Si(pincer)2 structure has been performed using a functional and basis set based on a combination of the Hartree-Fock method and density functional theory using the Becke-Lee-Yang-Parr exchange-correlation potential.

Electron absorption spectrum graph for [Si(pincer)2]0 structure
TD-DFT calculations reproduce the observed electron spectrum

Molecular orbitals involved in intensive transitions of the [Si(pincer)2]0 structure
HOMO - Highest occupied MO
LUMO – Lower unoccupied MO

Finite fully optimised structures Si[(ttpy)2]+n

Electronic absorption spectra of the complex [Si(ttpy)2]+n :
blue line, n = 4 ;
red line, n = 2 ;
green line, n = 0

Molecular orbitals involved in intensive transitions of the [Si(ttpy)2]+4 structure

Molecular orbitals involved in intense transitions of the [Si(ttpy)2]+2 structure

Molecular orbitals involved in intensive transitions of the [Si(ttpy)2]0 structure

The spectra of the [Si(ttpy)2]+n states are electrochemically generated
at -0.245 V (blue line, n = 4),
-0.520 V (red line, n = 3),
-0.945 V (grey line, n = 2),
-1.370 V (yellow line, n = 1),
and -1.695 V (green line, n = 0)

Quantum-chemical calculation of the structural parameters of [Si(pincer)2]0 ; [Si(ttpy)2]+4 ; [Si(ttpy)2] +2 ; [Si(ttpy)2] 0 complexes has been performed by the DFT method and their electro-optical properties have been studied. The results obtained were compared with known experimental data.
Manipulation with the charge substituents of the Si(ttpy)2 complex can provide the desired electro-optical properties of the material. It is shown how the change in the charge of the complex with ttpy ligand affects the electronic absorption spectrum.
The probabilities of electronic transitions and the nature of the molecular orbitals involved in them are determined. From the visualized MOs we can say that all of them have the nature of π-orbitals and are localized on pyridine ligands.
Conclusion