Fluorescence Compounds Based On Pyridine As Electron Acceptor Unit With Twisting Molecular Structure And Their Acid Discoloration Property

In this thesis,novel organic fluorescence compounds with twisted molecular structure were designed and prepared,in which pyridine and phenylamine served as electron acceptor(A)unit and electron donor(D)unit,respectively.The molecular conjugation length was adjusted by introduced 9,9-dioctylfluorene as?bridge between D and A unit.Based on these fluorescence compounds,this thesis studied the relationship between the molecular structure and fluorescence properties,discussed detailed mechanism of acidochromic,and then explored the potential application in white-light organic light emitting diode(OLED)and p H probe.The detailed experiment content is listed as follows:(1)Organic fluorescence compound with twisted D-A structure was designed and synthesized,in which triphenylamine served as D unit and pyridine acted as A unit,respectively.It was titled as TPA-PD.In TPA-PD molecule,the torsion angle between TPA and PD was 49°,resulting in a low fluorescence quantum efficiency(?_PL=24.0%).During dropping trifluoroacetic acid(TFA)into TPA-PD solution,its photoluminescence(PL)spectra exhibited double emission peaks located at 444 and 575 nm,respectively.Increasing the dropping amounts of TFA,the PL intensity of emission peak at 444 nm weakened,however,that of emission peak at 575 nm increased.Therefore,white fluorescence emission can be realized via adjusting dropping amounts of TFA.In addition,TPA-PD films also showed acidochromic fluorescence properties,which can also be reversible by adding triethylamine(TEA).The white-light OLED based on TPA-PD films treated with TFA were fabricated,and expressed color coordinates of(0.36,0.38)and the maximum external quantum efficiency of 2.8%.(2)By introducing ? bridge of 9,9-dioctylfluorene between D and A units in TPA-PD molecule,organic fluorescence compound of TPA-F-PD with twisted D-?-A structure was designed and prepared.In TPA-F-PD molecule,the torsion angle between triphenylamine and fluorene was 38°,the torsion angle between pyridine and fluorene was 33°,which smaller relative to that in afore mentioned TPA-PD molecule,which led to increase fluorescence quantum efficiency(?_PL=52.0%).It was suggested that charge transfer(CT)characteristic was enhanced with increasing molecular conjugation length,for example,the TPA-F-PD molecule was constructed by insertion of fluorene unit in TPA-PD molecule,which resulted in redshift of emission peak(460 nm)in PL spectrum of TPA-F-PD relative to that of TPA-PD(439 nm).TPA-F-PD exhibited obvious fluorescence properties of acid discoloration.During dropping TFA into TPA-F-PD solution,its PL spectra expressed dual emission peaks located at 460 and 650nm,respectively.Increasing the dropping amounts of TFA,the PL intensity of emission peak at 460 nm weakened,however,that of emission peak at 650 nm increased.Therefore,white fluorescence emission can be realized via adjusting dropping amounts of TFA.In addition,TPA-F-PD films also showed acidochromic fluorescence properties,which can also be reversible by adding TEA.Based on emission layer TPA-F-PD films treated with TFA,the white-light OLED were fabricated by controlling the content of TFA,and expressed color coordinates of(0.44,0.33)and the maximum external quantum efficiency of 2.1%.(3)Organic fluorescence compound with twisted A-?-D-?-A structure was designed and synthesized,titled as CzPA-F-PD.In CzPA-F-PD,N-(4-aminophenyl)carbazole(CzPA)and pyridine acted as D and A units,respectively,which was connected by?bridge of fluorene unit.In CzPA-F-PD molecule,the torsion angle between pyridine and fluorene was 20°,the torsion angle between fluorene and N-(4-aminophenyl)carbazole was 44°,which was the smallest among three compounds involved in this article,leading to the highest fluorescence quantum efficiency(?_PL=67.7%).It can be found that further increasing the molecular conjugation length can enhance CT characteristic of excited state of CzPA-F-PD,which resulted in the biggest redshift of emission peak(470 nm)of CzPA-F-PD among three compounds.CzPA-F-PD presented remarkable acidochromic fluorescence properties.During dropping TFA into CzPA-F-PD solution,its PL spectra expressed two emission peaks located at 470and 643 nm.Increasing the dropping amounts of TFA,the PL intensity of emission peak at 470 nm weakened,however,that of emission peak at 643 nm increased.Therefore,white fluorescence emission can be realized via adjusting dropping amounts of TFA.In addition,CzPA-F-PD films also showed acidochromic fluorescence properties,which can also be reversible by adding TEA.Based on emission layer CzPA-F-PD films treated with TFA,the white-light OLED was fabricated by controling the amounts of TFA.When the volume ratio between CzPA-F-PD and TFA was 5000/1,the best white-light OLED was acquired,which showed such excellent device performance as color coordinates of(0.36,0.37),the maximum external quantum efficiency of 4.1%that is close to theoretical limited value(5.0%)of typical fluorescence OLED.