Synthesis,Structure And Photochemical Properties Of Pyrazolone Derivatives

The emission wavelength and intensity of compounds with aggregation induced emission(AIE)in the solid or aggregation state can be modulated by forming different twisted conformations and accumulation patterns,which endows these materials with promising applications in biological probes,sensors,and organic light-emitting diodes,etc..Pyrazolones exhibits the photochromism and high fatigue resistance in the solid state.Moreover,it also shows AIE properties.However,the AIE mechanism and the relation between structures and properties are still vague.Herein,1-phenyl-3-substituent-5-pyrazolone was studied as the main object.Through structural modification,pyrazolone anils and pyrazolone salicylaldehyde hydrazones were prepared.AIE mechanism and the effect of different substituents on AIE properties of pyrazolone derivatives were systematically investigated.Besides,the relationship between structure and photochemical properties was unravelled.The main contents and results are summarized as follows:1.Three compounds 1-phenyl-3-methyl/benzyl/phenyl-5-pyrazolone(PMP/PCPP/DPP)were synthesized,which exhibited fluorescence properties.The emission wavelength showed the bathochromic effect and the intensity was increased along with the substitution of stronger electron-withdrawing groups at 3-position(phenyl>benzyl>methyl)and the increase of the molecular conjugation.Among them,1,3-diphenyl-5-pyrazolone exhibited the strongest emission intensity.Three isomers(NH-form,OH-form,CH-form)of 1,3-diphenyl-5-pyrazolone(DPP)with different colors were obtained by the recrystallization using three different solvents(anhydrous ethanol,acetone,chloroform).Their structures were characterizeed by1 H NMR,X-ray powder diffraction analysis.The photochemical properties were studied by UV-vis spectra and fluorescence emission spectra.It was found that the isomers showed good luminous performance and AIE properties.Based on fluorescence spectra at low temperature,the AIE behaviors could be caused by the restriction ofintramolecular rotation(RIR)and J-aggregate formation.Among them,the product recrystallized from acetone showed the best performance.In addition,luminescent thin film was prepared by DPP recrystallized from chloroform with polystyrene(PS),which showed similar fluorescence properties like the powder.A series of 4-acyl pyrazolone compounds were prepared by introducing various substituents at4-position of pyrazolone ring: 1,3-diphenyl-4-acetyl/benzoy/phenyl acetyl-5-pyrazolone(DPEP/ DPBP/DPCP).The relationship between structure and performance was further researched.They showed the AIE behavior due to the restriction of intramolecular rotation(RIR).All the compounds exhibited emission intensity in order of DPEP>DPCP>DPBP.The order of the steric effect and the molecular conjugation formed between pyrazolone ring and the substituent at 4-position is benzoyl>phenylacetyl>acetyl.2.Seven pyrazolone anils,1,3-diphenyl-4-acetyl/benzoyl/benzene acetyl-5-pyra zolone aniline(DPEP-AB/DPBP-AB/DPCP-AB)were synthesized through the condensation of 4-acyl pyrazolone and aniline.All the compounds exhibited AIE properties with emission intensity in order of DPCP-AB>DPEP-AB>DPBP-AB.The order of the steric effect and the molecular conjugation formed between pyrazolone ring and the substituent at 4-position is benzal>phenethyl>ethyl.Through the contrast of the orders mentioned above,it was found that the emission intensity are affected by both the steric hindrance and the conjugation.Among them,steric effect showed greater influence on the AIE property.Compared with 4-acyl pyrazolones,the fluorescence performance and AIE properties of DPEP-AB and DPCP-AB were improvedthrough the molecule coplanar and less steric effect.Then,1,3-diphenyl-4-(4-methyl/methoxy benzoyl)-5-pyrazolone aniline(DP4MBP-AB/DP4MOBP-AB)were synthesized.The effect of different substituents on the benzene ring at 4-position of pyrazolone aniline on structure and properties were discussed.It was found that the emission intensity of the compounds was relative strong when thesubstitutions at para position of benzene ring are methyl and methoxy group.Both of them showed AIE properties.The fluorescence of 1,3-diphenyl-4-(4-nitro benzoyl)-5-pyrazolone aniline(DP4NO2BP-AB)quenched when the para position is substituted by nitryl.The compound didn't show the AIE performance.3.Pyrazolone salicylaldehyde hydrazone compounds,1,3-diphenyl-4-acetyl/benzoyl /benzene acetyl-5-pyrazol-onesalicyloyl hydrazone(DPEP-SAH/DPBPSAH/DPCP-SAH),were prepared through the condensation of 4-acyl pyrazolones and salicylaldehyde hydrazine.The three compounds showed good luminous performance and AIE properties.The emission intensity was in order of DPBP-SAH>DPCP-SAH>DPEP-SAH.It indicated that the emission intensity was affected by the conjugation.Compared with 4-acyl pyrazolone,it was found that the AIE properties of pyrazolone salicylaldehyde hydrazones had been enhanced by increasing the conjugation of the compounds,which was realized through the elongation of the carbon chain length.