Synthesis And Characterization Of D-A Type Organic Electroluminescent Materials

Organic light-emitting diodes(OLEDs),as a new generation of display technology,have been recovered wildly attentions due to the advantages of self-emission,wide color gamut,and flexible preparation.Although OLEDs have been successfully commercialized,the development of high-efficiency,long-life red and blue light emitting materials are still a challenge due to the energy gap rules for red light emitting materials,and carrier injection and transmission balance for blue light emitting materials.Organic molecules with a Donor-Acceptor(D-A)type structure can balance the injection of carriers,which is attributed to the ability of transporting electrons and holes simultaneously and further improve the efficiency of the device.Therefore,emitters with D-A type are considered as an ideal architecture for building high-efficiency emitting materials.Based above emtioned,in this paper,three kinds of high-efficiency red and blue light emitting materials are constructed with D-A type are discussed:1.Six naphthalimide derivatives with D-A structure were synthesized and characterized.These derivatives employed naphthalimide group as the core.The effects of different donor units on the photoelectric properties of these materials were systematically discussed.Among them,the non-doped OLEDs constructed by MeOPA-NAI-Czet and PXZ-NAI-Czet as emitting layers(EML)exhibited red emission with a Commission Internationale de I?Eclairage(CIE)color coordinates of(0.66,0.33),which was very close to the requirements of the National Television Standards Committee(NTSC)Standard red of(0.67,0.33).The devices had a low turn-on voltage of 3.4 V.The maximum current efficiency(CE)of the devices based on MeOPA-NAI-Czet and PXZ-NAI-Czet were 0.22 cd A^-1 and 0.20 cd A^-1,respectively.The maximum power efficiencies(PE)were 0.22 lm W^-1 and 0.20 lm W^-1,respectively.The maximum external quantum efficiencies(EQE)were 0.32%and 0.33%,respectively.2.Two dibenzoquinoxaline derivatives with D-A structure were synthesized and characterized.Dibenzoquinoxaline and carbazole were used as core and donor unit,respectively.The relationship between the number of fluorines substituted on the dibenzoquinoxaline and the optoelectronic properties of the materials was discussed.Among them,non-doped OLEDs employed CzP-FPhe and CzP-DFPhe as EML achieved green-yellow emission and low turn-on voltage below 5.0 V.CzP-FPhe modified by one fluorine atom and CzP-DFPhe modified by two fluorine atoms had maximum CE of 1.65 cd A^-1 and 2.46 cd A^-1,respectively.The maximum PE were 0.89 lm W^-1 and 1.84 lm W^-1,respectively.The maximum EQE were 0.59%and 1.00%,respectively.3.Three D-A structure carbazole derivatives CzDP-BZ,CzNap1-Bz,and CzNap2-Bz were builded with carbazole as the donor unit and benzonitrile as the acceptor unit.The highest occupied molecular orbitals(HOMO)of CzDP-BZ,CzNap1-Bz,and CzNap2-Bz were 5.57 eV,5.53 eV,and 5.50 eV,respectively,which proved that the number of benzene rings connected at the 3 and 6 positions of the carbazole group and the difference in the bonding position had affected the HOMO energy levels and the properties of molecules,which could provide theoretical and experimental guidance for the design of blue light emitting materials with wide band gap.