Design,Synthesis And Study Of Optical,Electrical And Magnetic Properties Based On Functional Narrow Band Gap Conjugated Small Molecules

Due to their flexible spectral selectivity,mechanical flexibility,and structural diversity,organic semiconductor materials have found diverse applications in fields such as organic solar cells,organic field-effect transistors,and organic light-emitting diodes.Typical organic semiconductor materials include organic polymers and small molecules.Organic semiconducting molecular materials with narrow band gaps possess superior conductive properties compared to their wider band gap counterparts,as they are more susceptible to charge transfer.In addition,narrow bandgap organic conjugated small molecule materials exhibit exceptional optical,electrical,and magnetic properties.This thesis focuses on investigating these materials in three directions,namely quinonetype oligomers based on thieno-thiophene,D-A-D type small molecules with benzothiadiazole as the acceptor,and D-A type diradical small molecules.Its main aim is to examine the optical,electrical,and magnetic characteristics of these narrow bandgap organic conjugated small molecules in organic semiconductors through the following research aspects:(1)A series of quinone oligomers(OTTO,O2 TTO,and O4TTO)with varying quantities of thienothiophene(TT)units were synthesized and designed for the purpose of studying their optical,electrochemical,and electrical properties.Our findings indicate that as the conjugation length of the molecules increased,a significant redshift in the absorption spectrum was observed.O4 TTO exhibited absorption in the near infrared(NIR)region of 750-1000 nm with a narrow absorption peak in solution,while almost no absorption was observed in the visible region of 400-750 nm,resulting in close to transparency.These results suggest that by altering the conjugation length of quinone small molecules,we can produce small molecules capable of selectively absorbing light.This finding provides valuable guidance for the design of near-infrared dyes and plays a crucial role in the development of optical devices such as filters or light detectors.(2)Two D-A-D small-molecule wires with narrow band gap were synthesized by utilizing benzothiadiazole as the acceptor unit and benzene as the donor unit.The two molecules were named PTA,which has a unilateral anchoring group,and BTD,which has a bilateral anchoring group,respectively.The ability of the two polar molecules with narrow band gap to undergo π-πstacking interactions was analyzed using scanning tunneling microscopy break junction(STM-BJ)technology.Single molecule conductance tests were carried out,successfully demonstrating the conductance across the molecules.The results indicated effective charge transfer through the interaction between molecules and confirmed that the polar molecules in solution undergo π-π stacking interaction.This study not only introduces a novel method for achieving supramolecular interaction,but also intends to serve as a basis for the design and application of large-scale semiconductor materials.(3)Two small molecules containing stable nitronyl nitroxide diradicals were designed and synthesized.Molecule D1 contained only trianiline as the coupling unit,while molecule DA1 contained trianiline-benzothiadiazole as the coupling unit.By comparing optical,electrochemical,and spin properties,it was found that D1 exhibited a ground state singlet,while DA1 exhibited a ground state triplet.This was attributed to the D-A structure in DA1 promoting intramolecular charge polarization,resulting in partial spin on the coupling unit,which in turn affected the spin interaction between the two radicals in the side chain through superexchange interaction.These findings offer a novel approach for developing ground-state three-wire organic spin materials and provide a theoretical foundation for investigating the intrinsic relationship between coupling elements and spin interactions.