Photochromic, Aggregation-induced Emission And Self-assembly Behavior Of Pyrazolone Derivatives

Organic light-emitting materials have attracted much attention on account oftheir potential applications in organic light-emitting diodes, field-effect transistors,solar cells, chemistry and biological sensors, etc. In2001, Tang and co-workersobserved a phenomenon of aggregation-induced emission (AIE) which overcomes theaggregation-caused quenching (ACQ) effect in solution, and makes them easily applyto practical life. Pyrazolones derivates exhibit reversible photochromic properties andhigh fatigue resistance in the solid state. However, the fluorescence emission ofpyrazolone compounds is weak in solution, which limits the application in the real life.When they form aggregations, the fluorescence emission can be significantlyenhanced, which indicates that pyrazolones exhibit AIE characteristic. These resultsnot only expand the range of application on opyrazolone compounds, but also enrichthe system about aggregation-induced emission.In this paper, four kinds of pyrazolone phenylsemicarbazones [1,3-diphenyl-4-benzal/3-fluorinebenzal/3-chlorobenzene/3-bromobenzene-5-hydroxypyrazole4-phenylsemicarbazones，DPBP/DP3FBP/DP3ClBP/DP3BrBP-PSC] are choosed asthe research objects.Aggregation-induce emission properties, mechanism andself-assembling process about pyrazolone phenylsemicarbazones were systematicallyinvestigated. The effects of different substituents of pyrazolone derivatives onaggregation-induced emission properties, and water content and aging time on themorphologies of aggregates were discussed in detail. The relationship betweenstructure and AIE properties was obtained. The main results were as follows:First, one novel compound on1,3-diphenyl-4-(3-fluorinebenzal)-5-hydroxypyrazole4-phenylsemicarbazide(DP3FBP-PSC) was synthesized. Itscomposition and structure of the compound were characterized by MS spectra,1HNMR and IR spectra etal. It has found that DP3FBP-PSC has good photochromic properties and high fatigue resistance. The photochromic properties andphotochemical kinetics were studied by solid-state UV-vis absorption spectra andfluorescence emission spectra. Moreover, we have also found that the compound hasaggregation-induced emission effect in solution. Based on fluorescence spectra at lowtemperature and UV-vis absorbance spectra, the synergistic actions of the restrictionof intramolecular rotation (RIR) and J-aggregate formation were speculated to resultin AIE behaviors.Second, the effects of different substituents on the pyrazolone derivatives onaggregation-induced emission properties were investigated. For1-phenyl-3-substituent-5-pyrazolones, the compound introducing benzene ring at the3-position has excellent AIE properties due to the increase of conjugacy. For1,3-diphenyl-4-acyl-5-hydroxypyrazole4-phenylsemicarbazones, fluorescence wasquenched when the benzal group is at the4-position. It may be coplanar between thecarbonyl and benzene at the4-position. However,1,3-diphenyl-4-substituentl-5-hydroxypyrazole4-phenylsemicarbazones have goodAIE behaviors due to the increase of conjugacy in comparison with the4-acylpyrazolones phenylsemicarbazones. When halogen atoms were introduced into thephenyl at the4-position of pyrazolone phenylsemicarbazones, the fluorescenceintensity decreased, and the maximum emission is obviously blue shift due to theheavy atom effect and the electron spin-orbit coupling function of phosphor. For1,3-diphenyl-4-benzal-5-hydroxypyrazole thiosemicarbazones, the fluorescenceemission enhanced with the growth of the side carbon chains.Third, self-assembly behaviors for four kinds of pyrazolone4-phenylsemicarbazones in the aggregation state were studies. Effects of watercontent and the aging time on the morphologies of aggregates were discussed. Wefound that zero dimensional nano-structures were self-assembled to one dimensional nanostructures in the ethanol-water mixing system of pyrazolone4-phenylsemicarbazones with the increase of water content and aging time during theformation of aggtegates. Furthermore, the fluorescence emission intensity of1Dnano-aggregates is higher than that of nanoballs, which indicates that morphologies ofaggregates play an important role in controlling the aggregation induced emissionproperties.