Synthesis Of Conjugated Oligomeric Optoelectronic Materials Via Direct C–H Arylation Reactions

Organic functional ?-conjugated semiconductor materials are low-cost,and then can large-scale product flexible optoelectronic devices and wearable electronic devices by roll-to-roll technology,so that those materials have been popular with people.Those materials have been widely used in the fields of organic light-emitting diode(OLED),field effect transistor(OFET),organic solar cell(OPV),dye-sensitized solar cell(DSSC)and perovskite solar cell(PSC),which can be divided into polymers(MW>10,000),small molecules(MW<1,000)and oligomers(1,000?MW?10,000).Therein,the small molecule with the definited structure,but limited ?-electron conjugation and molecular weight,which restrained the improvement of corresponding device;polymers have high average molecular weight,but mixtures with different degrees of polymerization;However,high molecular weight oligomers combined with the characteristics of a small molecule with a single component and monodispersed polymer(PDI=1).Therefore,photoelectric oligomers with a defined structure and high molecular weight combine with the advantages of small molecules and polymers in terms of charge mobility,film formation characteristics,material purity,phase separation,and morphology,etc,which is expected to be an ideal candidate for organic optoelectronic devices.In recent years,research has been already aroused significant concern to find simple and convenient synthetic methods with the rapid development of organic electronics and the emergence of its commercialization.Direct Arylation of C–H Bonds(referred to as direct C–H arylation)prepare conjugated compounds in a high atomic economy.The aim of this paper is to synthesize new and long-chain conjugated oligomers via direct C–H arylation.The main research contents are as follows:(1)A series of novel phenyl-cored DPP molecules,including five meta-phenyl-cored molecules and four para-phenyl-cored molecules,have been synthesized in moderate to good yields,in a facile manner,through the Pd-catalyzed direct arylation of C–H bonds,and their optoelectrical properties have been investigated in detail.All new molecules have been fully characterized by NMR,MALDI-TOF MS,elemental analysis,UV-visible spectroscopy,and cyclic voltammetry.This synthetic strategy has evident advantages of atom-and step-economy,compared with traditional cross-coupling reactions.(2)A new synthetic concept for ?-conjugated oligomers has been developed by simply tuning the molar ratio between two co-monomers to switch the standard polymerization to one-step oligomerization.Three diketopyrrolopyrrole(DPP)-based conjugated oligomers sequentially consisting of 3,5 and 7 monomers and molecular weights of several thousand can be simultaneously produced in a single pot by C–H activated oligomerization and readily separated by a single chromatographic column with acceptable yields,demonstrating that the present synthetic strategy for large conjugated oligomers is atom-,and step-economic.(3)A series of monodisperse oligo[cyclopentadithiophene(CPDT)-co-difluorobenzene(DFB)]s with the stepwise increasing molecular length containing 3 to 15 novel units were synthesized via one-pot C-H direct arylation reaction,and chain-length-dependent photophysical properties was studied in details.All these new oligomers have been characterized and verified by NMR,MALDI-TOF MS,CV,DFT,photoluminescence(PL)spectra and UV-vis absorption spectra.Design artificial oligomer mixtures with precise composition and monomer sequence by controlling mixing ratio will lead to unique and tunable optical properties.This study confirmed that using mixtures of discrete oligomers is a good strategy to tune photophysical properties,exhibiting promising potential in light-emitting diode application.