Design,Synthesis,Assembly Of N-Type Small Molecular Semiconductors And Their Applications In Organic Field-Effect Transistors

Organic semiconductors have attracted great attention due to their advantages such as structural tunability,flexibility,solution processbility and low cost.They are widely used in organic light-emitting diodes（OLEDs）,organic photovoltaic（OPVs）and organic field-effect transistor（OFETs）.According to the charge types,they are mainly divided into two categories:p-type semiconductors with holes as carriers and n-type semiconductor materials with electrons as carriers.However,due to the fact that n-type semiconductors are easily captured by O₂,H₂O,and hydroxyl groups on the surface of the insulation layer during electron transport,their air stability is relatively poor,resulting in their device performance being relatively backward compared to p-type semiconductors.On the other hand,TCNQ,naphthalene diimides perylene diimides and fullerene derivatives are commonly used to build n-type semiconductor,which are relatively limited.Against this background,the thesis focused on the design,synthesis,assembly,and device optoelectronic performance of novel n-type organic small molecule semiconductors.The specific research has the following three aspects:（1）The lowest unoccupied molecular orbital（LUMO）energy level of the compound is the key to determine the material performance.The introduction of chlorine atom in the strong electron withdrawing unit into the chemical structure can reduce the LUMO energy level and achieve electron transporting.We developed a series of chlorine substituted N-heteroacene analogues:O4Cl,S4Cl,8Cl,and 12Cl.Among them,the electron mobility of O4Cl single crystal organic field-effect transistor can reach 0.04 cm² V^-1 s^-1 under ambient atmosphere,and the effectiveπ-πoverlap in the crystal structure ensures the electron transporting.This study indicates that the chlorine atom substitution design strategy is an effective method for developing n-type organic semiconductors.（2）Westudiedtheoptoelectronicpropertiesof4,13-bis（（triisopropylsilyl）ethynyl）benzo[b][1,2,5]thiadiazolo[3,4-i]phenazine-6,11-dione.The nitrogen atom and strong electron withdrawing carbonyl group reduce the LUMO energy level of the compound to-3.94 e V.Single crystal XRD diffraction indicated the presence of strongπ-πinteractions and abundant intermolecular short-contacts interaction in DITQ single crystals.DITQ ribbon like microcrystals were prepared by drop-casting method,and the growth direction was proved to beπ-πstacking direction（a-axis）.The single crystal devices exhibited excellent electron transfer performance,with a maximum of 2.55 cm² V^-1 s^-1.After being placed in air condition for one week,the mobility remained as high as 1.74 cm² V^-1 s^-1,showing good air stability.（3）A novel A-D-A organic semiconductor（FIMIC）was designed and synthesized by introducing D-A type terminal group to expand theπ-conjugated structure of lactam:2,2’-（（2Z,2’Z）-（（6-（2-ethylhexyl）-5,7-dioxo-3,9-diundecyl-6,7-dihydro-5H-thieno[2’,3’:4,5]thieno[2,3-e]thieno[2’,3’:4,5]thieno[3,2-g]isoindole-2,10-diyl）bis（methaneylylidene））bis（3-oxo-2,3-dihydro-1H-indene-2,1-diylidene））dimalononitrile.Theoretical calculations revealed that the LUMO orbital of the compound is highly delocalized along theπ-conjugated core,and the LUMO energy level was-3.88 e V.OFET based on FIMIC thin-films prepared by spin-coating method showed unipolar electron transport at room temperature,and the highest electron mobility after annealing was 3.5×10^-4 cm² V^-1 s^-1.The light response performance of FIMIC thin film transistors was further investigated by introducing light at 510 nm and 610 nm wavelengths,proving that the A-D-A material has good application prospects in the field of photodetectors.