Synthesis And Properties Of Organic Semiconductors Containing Pyridalthiadiazole And Isoindigo Acceptors

Organic semiconductor materials exhibit broad application prospect in organic field-effect transistors(OFETs),organic light-emitting diodes(OLED)and organic photovoltaic(OPV)due to their unique optical,electric and magnetic properties.Therefore,the exploitation of novel organic semiconductor materials become a hot topic in organic eletronics.In this dissertation,two molecular design strategies,including "regioregular dual-acceptor strategy" and "extending ?-conjugate backbone",were used to develop two kinds of donor-receptor(D-A)organic semiconductor materials,in which pyridal[2,1,3]thiadiazole and isoindigo derivatives are served as acceptor units,respectively.In addition,we also studied the relationship between the structure and performance of the as-synthesized materials.The main research contents are as follows:1)Due to highly electron-withdrawing nature and good coplanarity,pyridal[2,1,3]thiadiazole(PT)has been widely used for the development of high-mobility p-type polymer semiconductor materials.However,no ambipolar transport performance was observed in any of PT-based polymer materials.Herein,We design and synthesize a regioregular bis-pyridal[2,1,3]thiadiazole(BPT)unit by linking two PT units together,and the first PT-based ambipolar copolymer PBPTV was developed based on the developed BPT unit.Moreover,a comparative study has been performed to reveal the thermal properties,solubility,photophysical properties,electronic properties,and ordering structures of the PBPTV polymer.Compared with the PT unit(LUMO =-3.13 eV),the BPT unit displays lower LUMO level(-3.42 eV)and stronger electron affinity.Therefore,the BPT unit significantly improves the electron affinity of the PBPTV,thus endowing PBPTV with suitable HOMO and LUMO level values of-5.61 and-3.66 eV,respectively.The surface morphology and crystallinity analysis of thin films reveal that PBPTV thin films show uniform surface topography and close lamellar structure;moreover thermal annealing obviously improves the continuity and crystallinity of the PBPTV thin films.Using PBPTV thin films as acitive layer,top-gate bottom-contact(TGBC)FET devices exhibit air-stable ambipolar charge transport due to good encapsulation effect of PMMA dielectric layer.Under the 20%-40%air humidity,the best-performing FET device shows the highest hole and electron mobilities of 6.87 and 8.49 cm2 V-1 s-1,respectively.2)Due to strong electron-deficient ability,highly coplanar backbone,and versatile modular structure,isoindigo(IDG)has been widely used as an excellent building block for the development of novel organic/polymeric semiconductor materials.In this section,a series of highly 7c-extended D-A-D type tetrathienyl-fused isoindigo semiconductors(TT-IDG,including symmetric and asymmetric TTIDG derivatives)are designed and synthesize via FeCl3-catalyzed intramolecular cyclization reactions.The results reveal that this cyclization reactions can be influenced by alkyl substituted groups of IDG derivatives.When the substituted group is n-octyl,n-dodecyl,and bromine group,the intramolecular cyclization reaction of IDG derivatives can be achieved successfully,giving yields of over 72%.However,polymerization of IDG derivatives is observed when the substituted group is n-dodecylthio groups.In addition,the thermal stability,photophysical,and electrochemical properties of our developed TT-IDG are investigated.The results show that the TT-IDG derivatives have good thermal stability(Tg>375 ?),broad absorption spectra(300-700 nm),and air-stable HOMO energy levels.