Design And Synthesis Of Organic Luminescent Materials Based On THTBT Derivatives And Evaluation Of Their Photophysial Properties

Organic materials,which are based on the aggregation of organic molecules,have been fairly applied in the electronic devices such as light-emitting diodes,solar cells,thin film transistor and molecular switches.Howerver,the performance of organic device is far from that of inorganic one,thus the development of organic materials with extraordinary optical and/or electronic properties is the key issue in this field.Especially,organic materials originated from the "donor-acceptor(D-A)" type molecules have currently attracted widespread interests.In this thesis,we have designed and synthesized a series of organic molecules with D-A type structures.The electron-rich conjugated heterocycles are employed as the key skeleton,and followed by introducing the electron-withdrawing substituents to constructure the D-A structures.Based on the thorough investigation of their photophysical and electrochemical properties,we have clarified the structure-property relationship of these systems.The main content of each chapter is as followings,In Chapter 1,we firstly made the brief introduction about the features of organic molecules with D-A structure.Then,we focus on their applications in organic light-emitting diodes,solar cells,thin film transistor and molecular switches.Finally,our strategies on molecular design and synthesis were outlined.In Chapter 2,we report the synthesis of the title D-A type molecules.The electron rich heterocycle THTBT,which contains S and N atoms,was employed as the key skeleton(THTBT = 2,3,4-Tetrahydro[1,4]thiazino[4,3,2-de][1,4]benzothiaxine).The D-A type molecules were firstly achieved by Friedel-Crafts(FC)reaction of THTBT with a series of RCOCl to form the benzophenone derivatives,which were then transformed to the corresponding D-A type styrene analogues through the McMurry reaction.It should be noted that THTBT has two active sites for FC reaction,say,the para-and ortho-positions of N and S atoms respectively.By carefully modulating the reaction temperature and the amount of Lewis acid,we have selectively synthesized each isomer of the FC reaction product.Because it was difficult to isolate the cis-and trans-isomers of styrene derivatives,we only got the mixed products.Morover,we found that benzophenones bearing strong electron-withdrawing substituents(C6F5,4-NO2-C6H4)could not afford the desired styrenes through the McMurry reaction.The solid state structures of several styrene derivatives were analyzed via the X-ray single crystal diffraction.In Chapter 3,we report the photophysical and electrochemical properties of the above benzophenones derivatives.The absorption spectra demonstrate that,(i)when the substituent is at the para-position of N in THTBT,the absorption band shows red-shift as the electron-withdrawing ability of substituent increases;(ii)when the substituents is at the ortho-position of S in THTBT,there is no clear relationship between the absorption band and electronic nature of substituent.These compounds show the positive solvatochromism as proved by the red-shift of emission band with increasing solvent polarity.In the case of compound with strong electron-withdrawing substituent(CF3,C6F5,4-NO2-C6H4),the emission was completely quenched in polar solvent such as DMF,suggesting that the intramolecular charge-transfer occurs in the excited state.Moreover,these compounds can be employed to recognize Pd2+,as proved by the formation of new absorption band in the visible region(400-600 nm)as well as the quench and/or blue shift of the emission.These benzophenones derivatives possess a quasi-reversible redox waves,which corresponds to the redox wave of THTBT framework.