Study Of Oxygen-embedded Linear Conjugated Molecule And Five-membered Ring Incorparated Nono-conjugated System

Conjugated molecules are relatively inexpensive,easy to chemically modify and process,and they can realize the control of electronic structures and electron motions in the region and the regulation of molecular aggregation states,leading to rich optical,electronic and magnetic properties with great prospects for application in the field of optoelectronic and magnetic functional materials.Among them,a typical conjugation system is graphene-like fragments,consisting of benzene ring as the basic structural unit.The successive fusion of multiple benzene rings and the corresponding fusion directions can form unique topological structures.For example,acenes,a family of linear conjugation system,featuring long zigzag edges,have been widely investigated in organic semiconductor due to their effective charge injection and favorable carrier mobility.Electronic structure of conjugated molecules plays an essential role in controlling of optoelectronic and magnetic properties of molecule-based material,which is viewed as the source of functions of these systems.Therefore,researchers normally think about how to regulate electronic structures of conjugated molecules.Our study in this thesis has developed two strategies to fine-tuning of electronic structure of conjugated systems: 1)the oxygen-doped strategy,that is,precisely introduced oxygen atoms into the conjugated framework,resulting in control of the?-electron distribution,dipole moments and molecular energy gap;2)the non-benzene units,such as electron-withdrawing five-membered ring viewed as "defects",were introduced into the molecular framework to form a defect-type structure and achieve the purpose of electronic structure control.In addition,this paper is also devoted to the development of new synthetic methods and techniques,as well as the exploration of the evolution of novel molecular structures and their physical properties,aiming to provide references for the design and preparation of functional molecular materials and their applications.The main contents are as following:(1)The intrinsic high instability of higher order acene causes its practical synthesis very difficult,so we have developed a way to construct oxygen-doped acenes with oxygen-atoms precisely doped at specific positions,and thus obtained oxygen-embedded quinoidal pentacenes and nonabenzenes with zigzag O-embedding at the edges,which overcame the hindrance of ?-electron communication by O-embedment.Besides,we have characterized their physical properties and fabricated OFET devices based on molecular material.Furthermore,we have investigated the oxidation state of acene compounds by chemical approaches,revealing their high stability and the characteristics of their electronic structure.(2)On the basis of the non-planar perylene building block,we have designed and synthesized a series of ?-extended molecules with fused five-membered rings,named as G1,G2 and G3 which have visible and infrared electronic absorptions.Experiments also demonstrated that the incorporated five-membered rings are favorable to delocalization of ?-electrons especially in non-planar systems.Interestingly,large-size molecule G3 exhibit a new absorption band in the near-infrared region as increasing concentration.This new band could be attributable to newly-formed dimer at excited state.(3)By using the perylene unit as the molecular building block,a series of nano-size conjugated molecules with continuously fused five-membered ring(DIP,D-DIP and T-DIP)were successfully prepared by wet synthesis through developing mature reaction conditions and cyclization methods.The chemical structures of these compounds were then characterized by NMR and mass spectrometry as well as single-crystal XRD analysis to reveal their ground state molecular conformation and conjugation characteristics.(4)Taking the above-mentioned nano-sized molecules as a model,we have systematically explored their optoelectronic properties,and revealed the correlation law between their electronic structures and properties.It is shown that with the increase of molecular size,the conjugated system has an enhanced ability to absorb photons,and on the other hand,multiple redox properties appear.We have characterized their physical properties and fabricated OFET devices based on nano-sized molecules.