Aggregation-induced Emission Properties And Multi-stimuli Response Behaviors Of Aryl-substituted Pyrrolopyrrole Derivatives

Organic solid luminescent materials with stimuli-responsive emission properties considered as smart materials have drawn great attention over the past years because of their promising application in mechano-sensors,data storage,and optoelectronic devices.These fluorescent molecules usually show tunable and switchable optical properties achieved by either controlling molecular arrangement or packing modes under the external piezo-,vapo-,thermos-stimuli conditions.It means the change of optical properties can be achieved by physical methods,which is prior to chemical synthesis technology.It is well known that the luminescence of a molecular system in the condensed phase depend on the packing modes of the molecules,and significant variation has been found according to the molecular aggregation state of the stacking mode(polymorphism).The acquisition of the crystalline structure in different phases(polymorphs)provides the best opportunity to investigate the relationship between molecular packing and optical properties.So,herein,we mainly focus on the synthesis of a series of 1,4-dihydropyrrolo[3,2-b]-pyrroles derivatives to investigate the relationship between structure,aggregate packing and optical properties.The main achievements in the dissertation are listed as follows:In chapter 2,in order to understand how the substituents and their position affect the solution and solid-state optical properties,a series of 1,4-dihydropyrrolo[3,2-b]-pyrroles derivatives were designed and synthesized.The 1,4-dihydropyrrolo[3,2-b]-pyrroles derivatives with electron-withdrawing groups on the 1-aryl and electron-donating groups or hydrogen atom on the 2-aryl showed AIE property.The analysis of the X-ray crystal structure proved that the AIE behavior was associated with the twisted conformations and crystal packing modes,the intermolecular interactions(C-H … ?)account for restricted internal rotations,leading to fluorescence enhancement.The density functional theory calculations further demonstrated that the complete separation of HOMO and LUMO is conducive to AIE behavior,which elucidated the substituent effect of the organic fluorophores on their photophysical properties.In chapter 3,bis(4-cyanophenyl)-4,4'-(2,5-diphenylpyrrolo[3,2-b] pyrrole-1,-4-diyl)dibenzoate(DPPCN)was synthesized and exhibited aggregation-induced emissionproperties.DPPCN was cultivated in different solvents getting three kinds of crystals,A,B,and C.Crystals of A and B were respectively blue and cyan-blue emissive.They all displayed CIE behaviors.The different kinds of co-effects of the solvent,intermolecular forces,molecular conformations and molecular packing modes endow DPPCN polymorphisms with multi-color emissions(from blue to yellow and up to 60 nm)and different fluorescence efficiencies.The emission color of crystal of A can be reversibly tuned by grinding and exposing to chloroform vapor and show a good reversible mechano-florochromic process.Crystal of A also exhibited thermo-stimulus fluorescence switching behavior.While the yellow emission C switched to the other colors(blue and cyan-blue).Basing on XRD analysis of single-crystalline structures,multicolor fluorescence tuning and switching are attributed to the nature of polymorphs,that is,a change of intramolecular conformation and intermolecular packing modes.These results are highly valuable for the further design of relevant compounds with tunable solid-state emissions.