Design, Synthesis And Optical Properties Study Of Multi-state Emission Fluorophor Based On Imidazole And Pyrrolopyrroledione

In recent years,organic small molecule fluorescent materials have become potential hot spots for researchers due to their potential applications in bioimaging,organic light-emitting diodes?OLEDs?,and chemical sensors.Since the 1970s,1,4-Diketo-pyrrolo[3,4-c]pyrrole derivatives?DPPs?was discovered,DPPs represented a class of brilliant red high-performance pigments having the exceptional light,weather and heat stability,and high light fastness and excellent optical properties,such as strong absorption and emission in the visible region,high fluorescence quantum efficiency and large two-photon absorption cross section,etc.Therefore,DPPs have become very important organic light-emitting materials.In this paper,a series of organic small molecule fluorescent materials based on1,4-Diketo-pyrrolo[3,4-c]pyrrole were designed and synthesized,and studied the relationship between their molecular structures and photophysical properties.The main contents are as follows:1.DPP is selected as electron acceptor?A?group and imidazole derivative as another electron acceptor?A'?group to design and synthesize two novel multi-acceptors organic fluorescent molecules?DPPBI and DPPPI?with A'-?-A-?-A'structure.We systematically studied the effect of changes in the conjugated structure of the electron acceptor?A'?group on the aggregation behavior and fluorescence properties of the molecules.Among them,the compound DPPBI with1,4,5-triphenyl-1H-imidazole?BI?as the second electron acceptor group,because the group has larger twisted structure and smaller conjugation than DPPPI,DPPBI powder emits orange fluorescent(?_PL=585 nm).Compound DPPPI with phenanthroimidazole?PI?as the second electron acceptor group,has larger conjugation planarity which increases its conjugation length.DPPPI solid-state powder emits near-infrared?NIR?fluorescent(?_PL=684 nm).Both compounds exhibit pronounce mechanohypsochromic luminescence,DPPPI solid displays the mechanohypsochromic shift luminescence with 73 nm of spectral shift.However DPPBI is a mechanochromic luminophor with red-shifted luminescence with 33 nm of spectral shift.Differential scanning colorimetry?DSC?and X-ray diffraction?XRD?analyses confirm that the phase transition between crystalline and amorphous states upon external stimuli is responsible for the reversible color change.2.Based on the compound DPPBI,we introduced triphenylamine?TPA?into the terminal moiety to design and synthesize TIDPP with D-A'-A-A'-D structure with BI as the adjacent acceptor-featured conjugation bridge?A'?and triphenylamine as the peripheral donor?D?.The resulting new DPP derivative TIDPP was a multi-branch molecule and exhibited unique multi-state emission properties.In molecular solutions,TIDPP was a yellow-emitting dye with the fluorescence efficiency of 70%,but the evaporated solid,spin-coated film and aqueous suspensions exhibited broad emission spectra ranging from 600-800 nm with still commendable fluorescence efficiencies of40-50%.Moreover,the aqueoussuspensionexhibitedthepromising aggregation-enhanced two-photon absorption cross section and excitation fluorescence,and TIDPP solid displayed the mechanohypsochromic shift luminescence with 50 nm of spectral shift?...