Theoretical And Applied Studies On The Optical Properties Of Porphyrin Derivatives With High Photoactivity

Porphyrin is a compound in which porphin is used as a parent,and is a generic term for homologues and derivatives of porphin rings plus different substituents.Porphyrin is a 16-center 18-electron large?-conjugated system with aromaticity.When two protons of the nitrogen of the porphyrin center are replaced by metal ions,a metal porphyrin complex is formed,which is widely present in nature.Due to its unique structure,low energy level difference,stable physicochemical properties and good photosensitivity,porphyrin molecules have been successfully used in many fields such as fluorescence analysis,electrochemiluminescence analysis,photovoltaic materials and solar cells.In recent years,dye-sensitized solar cells have developed rapidly and are widely used.However,its low conversion efficiency limits its practical application to varying degrees.Studies have shown that the factors that increase the efficiency of light conversion are mainly solar light,sensitizers,electrolytes and battery materials.One of the effective means to improve the efficiency of light conversion is to design sensitizer molecules with good performance.Among many different types of sensitizers,porphyrins have attracted much attention for their excellent optical properties.When selecting a specific sensitizer,the workload of designing the sensitizer molecule is large,and the quantitative calculation method helps to design the sensitizer efficiently and contributes to the evaluation of the performance of the solar device.Density functional theory?DFT?calculates the properties of the ground and excited states,analyzes the molecular orbital and charge density distribution,and characterizes the absorption spectrum of the sensitizer.By calculating the relevant parameters such as Voc and Jsc and other related parameters,D-?-A type sensitizer with excellent photoelectric properties was selected.This series of work provides theoretical support for the research on the light conversion efficiency of solar cells.As an experimental verification method,fluorescence detection technology has attracted extensive attention due to its advantages of simple operation,high sensitivity and short time-consuming.In this paper,the optical properties of porphyrins were studied by combining fluorescence detection techniques with quantitative calculations.The main work is divided into the following parts:Chapter one:This chapter reviews the structure,synthesis methods and applications of porphyrin compounds in daily life.The background and application of fluorescence analysis method are expounded,and the application research of porphyrin as a sensitizer in solar cells is introduced.At the same time,the principle,development and application of density functional theory are introduced.Chapter two:In this chapter,Time-dependent density functional theory?TD-DFT?and DFT method are used to study the novel porphyrin sensitizers in which seven donors were encapsulated by alkyl chain units and the receptors were replaced by phosphonic acids or carboxylic acids.The anchoring groups?phosphonic acid or carboxylic acid?are placed at different substitution sites,and the photoelectrochemical properties of the sensitizer are discussed based on their frontier molecular orbital energy and light absorption.And compared with known TPP.Chapter three:Based on the research of the related contents in Chapter 2,seven dye sensitizers with D-?-A sequence were designed.The structure and properties of the ground states of different substituted porphyrin dye molecules were studied by DFT method.The structure and properties of excited porphyrin dye molecules were studied by TDDFT method.The effects of different substituents on the energy and charge separation state of porphyrin sensitizer orbitals were investigated.According to the related parameters of open circuit photovoltage(J_SC)and short circuit current density(V_OC),the influence of the change of orbital energy level of different?bridge molecules on the dye performance is calculated,which makes it have a wider absorption band and easy to separate intramolecular charge.At the same time,a suitable?bridge was selected as a porphyrin sensitizer candidate,and a new porphyrin sensitizer which is both efficient and stable was designed.Chapter four:Designed a"Turn off"type of 5,10,15,20-?4-sulfonic acid phenyl?porphyrin-Fe²⁺fluorescent probe for the detection of hydrogen peroxide and glucose in actual samples.The synthesis method of TPPS₄ is improved,and the synthesis process is more environmentally friendly and the yield is higher.It was characterized by NMR,Fourier Transform Infrared Spectroscopy and Ultraviolet Absorption Spectroscopy to prove the successful preparation of TPPS₄.Then,using the high fluorescence characteristics of TPPS₄,a sensitive fluorescence sensor for detecting hydrogen peroxide?H₂O₂?and glucose(C₆H₁₂O₆)was constructed.Finally,the structural properties of iron porphyrins with different valence states were analyzed theoretically in combination with the DFT method,which further explained why ferrous iron and porphyrin were used to form probes instead of ferric iron in experiments.At the same time,the fluorescence quenching mechanism in the detection process was analyzed.