Bay-functionalized And Nano-hybrid Amphiphilic Perylene Diimides: Synthesis And Self-assembly Behaviors

Perylene dimide (PDI), which has polycyclic aromatic hydrocarbon in structure withoutstanding stability, intense pi-pi interaction, spontaneously formation and strong photophysicalproperties, is a kind of unique molecular electronic materials and has wide applications in solarcell, biological probes, chemical inductor and so on. The photophysical properties andapplications of PDIs are largely depend on the molecular structures and condensed structures insolid state. To regulate and control the condensed structures of PDIs by hydrophobic/hydrophilicinteractions has drawn increasing research focus nowdays.Polyhedral oligosilsesquioxane (POSS) containing alkyl chains is a hydrophobic unorganicnanoparticle with diameter about0.78nm, which can conduct as a large substituent to modifysolubility and limit pi-pi packing; Triethylene glycol(TEG) having hydrophilic units with linearstructure and the end hyxyol group can form hydrogen bond with others, or be used as reactivegroup for further modification. Incorporation both of them into PDIs, what its self-assemblybehaviors will be like under the effects of multi-interactions? In this work, we design andsynthesis three POSS-PDI-POSS molecules with POSS as side chains and functionalized withH(unsubstituted), Br and triethylene glycol(TEG): POSS-PDIH-POSS, POSS-PDIBr-POSS andPOSS-PDITEG-POSS, respectively. And the main contents including their self-assembly behaviors,the structures in condensed state by self-assembly and photophysical properties in solid state wereinvestigated so that we can observe and understand their self-assembly behaviors undermulti-interactions. The main results are listed as follows.1. The1,6and1,7Isomers of POSS-PDIBr-POSS at bay position (with the same Rfvalue)was achieved by brominating PTCDA followed by reacting with amino POSS and then purified bycolumn chromatography. Then purified clean crystals of POSS-PDIBr-POSS substituted at1,7positions were achieved by recrystallizations. POSS-PDITEG-POSS was synthesized by introducing triethylene glycol into POSS-PDIBr-POSS with K2CO3and18-crown6-ether ascatalysts and purified by column chromatography and recrystallizations. The molecular structuresand high purities were clearly showed by means of FT-IR, NMR and MALDI-TOF, which laysfoundation for further self-assembly studies.2. UV-Vis absorption spectrum and fluorescence spectrum are general means reflectingself-assembly behaviors of PDIs in solutions. The accuracy, reliability and acquisition of testedresults are largely depending on molecular structures and solvents. In this work, the effects ofsolvents, concentrations and variety in bisolvents on self-assembly behaviors of POSS-PDI-POSSwere studied systematically and then a method including sample processing, valuation ofsolubility, solvent choosing and titration experiment used for locating key factors like solvent,concentration of PDIs was established for further study of the three molecules in self-assemblybehaviors. The results show that the absorption peak of POSS-PDITEG-POSS at567nmrepresenting0-0electron transition red shifts compared to those of POSS-PDIH-POSS andPOSS-PDIBr-POSS(524nm,522nm) and the fluorescent emissions locate at589nm,543nm and550nm respectively. It indicates that perylene was distorted and pi-pi interaction was disrupted bythe introduction of bromine and triethylene glycol, which was confirmed by molecular simulationsusing geometries optimized and energy calculations. All molecules can self-assembly in hexanoland the critical concentrations are1.24E-6M,1.8E-4M and4.8E-4M. The ideal bisolvents systemfor POSS-PDIH-POSS and POSS-PDIBr-POSS is n-propanol/1,4-dioxane while forPOSS-PDITEG-POSS is THF/water. The UV-Vis spectra of three molecules all showcharacteristics of dimer like broadening and ε0-0/ε0-1decreasing. But the aggregates formed byPOSS-PDIH-POSS exhibit fluorescent emission while others quenching indicating the differencesin configurations of dimer formed by these molecules.3. All the three molecules could form aggregates with specific morphology. And it wasshowed that both of POSS-PDIH-POSS and POSS-PDIBr-POSS form needle-like crystals whichwere discretely packed by dimers as units. There is so large longitudinal offset that thenaphthalene moieties form H-type dimers, which can explain the unique photophysical propertiesin POSS-PDIBr-POSS crystals: the crystal formed by POSS-PDIBr-POSS blue shift in fluorescentemission, which differs from red shift in PDI with linear alkyl at N-imides and substituted bybromine at bay areas, and low fluorescent quantum yield. The sphere particles formed byPOSS-PDITEG-POSS consist of flake-like aggregates and it was found that the flake aggregateswas packed regularly by dark color belts with inter-distance about2.7nm observed under highresolution TEM. The formation mechanism, deduced by temperature-dependent FT-IR, analysis ofmetastable ordered structures and the characteristics that dimer acting as packing unit inPOSS-PDI-POSS, was that dimers formed pack into layers followed by packing layer by layer and then aggregated into sphere crystals under the combined actions of hydrophobic/hydrophilic andhydrogen bonds.