Synthesis And Self-assembly Of Perylene Bisimides With Tertiary Amine Groups And Their Photophysical Properties

Since organic semiconductor materials can overcome the disadvantages such as poor ductility of inorganic semiconductor materials,they have attracted much attention in the field of optoelectronic functional materials.The strong conjugation between the electron-rich perylene core and the electron-withdrawing imide groups gives perylene bismide?PBI?the capability of transfering charge.PBI has excellent fluorescence properties,so PBI and its derivates have great potential and application prospects in the field of organic n-type semiconductors,fluorescent probes,etc.The large?-conjugated planar structure of PBI makes it easy for molecules to self-assemble into micro/nano aggregates,which can effectively realize the construction of material structure in molecular size.Besides,the performance of the PBI functional materials mainly depends on the morphology of the aggregates formed via self-assembly.Therefore,changing self-assembly driving forces by designing molecular structure and self-assembly environment appropriately,then adjusting the morphology and structure of aggregates to obtain new PBI functional materials is the research focus of PBI self-assembly.In this paper,four kinds of PBI derivatives containing tertiary amine groups were designed and synthesized.The morphology of aggregates formed in different self-assembly environments was investigated.The effects of molecular structure and self-assembly environment on the morphology and photophysical properties of aggregates were discussed.The contents and results are as follow:1.Four PBI derivates substituted by tertiary amino groups with different alkyl chain lengths?MDI-PBI,EDI-PBI,MPI-PBI and AEP-PBI?were synthesized.The successful synthesis of the target compounds was confirmed by nuclear magnetic resonance spectroscopy and infrared spectroscopy.2.These four molecules self-assembled in HCl_aq/THF containing hydrochloric with different acid concentration.The morphology and photophysical properties of the aggregates were characterized,and the structure of the four molecules was optimized.It was found that the aggregates formed by MDI-PBI,EDI-PBI and AEP-PBI have red-to-blue color change when the ratios?r?of the concentrations of H⁺to tertiary amine group were 3:1,5:1 and 20:1,respectively.And these molecules formed fiberous aggregates when r were in the range of 3:1-2500:1,5:1-15000:1 and7:1-2500:1.In additionally,the curvature of the fiberous aggregates increased with r.MPI-PBI also formed fibrous aggregates in the range of 3:1-7:1,but the aggregates did not have color change and bend.Four molecules formed J-type aggregates,and the fluorescence of all aggregates didn't quench.The maximum absorption peaks of blue MDI-PBI,EDI-PBI and AEP-PBI aggregates red-shifted from 570 nm to about620 nm,and the characteristic absorption peaks of emission spectrum had a Stokes shifts of approximately 30 nm.However,the maximum absorption peaks of the red aggregates formed by MPI-PBI only red-shifted to about 580 nm,and the emission spectra had a Stokes shift of about 60 nm.The optimized results of molecular structure indicated that the dihedral angles of EDI-PBI and AEP-PBI were close to 0°,while the other two molecules were about 13°.The optimized results of molecular structure were consistent with the results of morphology change.In addition,the bandgaps of four molecules were about 1.28eV,which meet the requirements of organic solar cell materials.The results of X-ray diffraction indicated that there were two different molecular stacking between blue aggregates formed by molecules such as MDI-PBI and red aggregates formed by MPI-PBI.A reasonable explanation of aggregates with different color was made based on the morphology and spectral data.3.MDI-PBI and MPI-PBI self-assembled in two organic solvent phase systems:methanol/THF,n-hexane/THF by phase transfer and rapid solution dispersion.The morphology,photophysical properties and molecular packing patterns of aggregates obtained by rapid solvent diffusion were mainly discussed.In organic solvent phase,the morpgology of MDI-PBI and MPI-PBI aggregates transferred from nanospheres to long nanowires or nanobelts under increasing solvophobic effect.MDI-PBI and MPI-PBI formed J-type aggregates in two self-assembly systems.The results of polarized light interference experiments showed that the driving forces in different directions of growing aggregates are different.In the case of V_methanol:V_THF=5:1,the?-?stacking was responsible for the elongation of nanobelts formed by MDI-PBI with respect to their long axis,while elongation in short axis direction was caused by solvophobic,which was just contrary to MPI-PBI.4.The?-?stacking,hydrogen bonding and charge interaction between sulfonated graphene?SGO?and R-PBI were utilized to obtain aggregates R-PBI/SGO-1 successfully.