Theoretical Study On The Switching Properties Of Azobenzene Derivatives

Azobenzene containing compounds have the aromatic rings connected by nitrogennitrogen double bonds(-N=N-).Azobenzene and its derivatives have two isomers,trans and cis.The reversible trans-cis isomerization process occurs when the external conditions such as light illumination and temperature change with the change of color and geometric structure.The relative energy between the trans and cis isomers will also change.Such characteristics are applied to many aspects such as molecular motors,molecular switches and energy storage.At the same time,azo dyes are also used as colorants in daily life.In the process of long-term contact with the human body,reduction reactions may occur,leading to the breaking of azo groups and the release of toxic aromatic amine compounds.It is of importance to find some important features to correleate with experimental results of amine detection.In this thesis,some molecular switches are designed to be capable of trapping metal ions.The binding energy between azobenzene derivatives and metal ions was calculated to evaluate its performance.Density functional theory(DFT)was used to calculate the free energy changes of azo reduction in different azo-containing molecules,and correlation analysis was carried out by comparing with experimental data to explore the indirect detection method of azobenzene.The main research contents are outlined as follows:Molecular switch is a kind of molecule which changes its conformation or structure under the stimulation of light,electric field and other external conditions.Among these molecular switches,there is a kind of interesing "scissor molecule" in which the azobenzene structural unit is used as the "axis".When photoisomerization occurs,the substituent part undergos changes between the ‘on' and ‘off' states.By introducing different metal ligands,we design a series of molecular switches that may capture various metal ions and calculate the binding ability of azobenzene molecular switches with metal ions by DFT.In most cases,azo dyes are not toxic,but those aromatic amine intermediates are dangerous.The common way of amine detection is to directly reduce azo molelules to the aromatic amines and to detect the resultant products.We select 10 common forbidden azobenzenes,and correlate the descriptors of the atomic number,the change in Gibbs free energy,the nitrogen-nitrogen bond length,and the atomic charges with the experimental data of recovery,relative standard deviation,retention time,maximum absorption wavelength with the Pearson correlation coefficient.The important descriptors are then found to predict the reduction of azobenzene derivatives to arometic amines.