Design,Synthesis And Properties Of Fluorescent Compounds Based On Aromatic Heterocyclic Ring Extension

In recent years,research on organic luminescent materials has attracted great attentions because of their importance in the applications of light technology such as signaling,imaging and fuorescent biosensor/chemosensor materials.Among them,materials bearing the "D-A" or "push-pull" structural architectures are fascinating,whose absorption and emission spectra are much redder than those pure cabon/hyhron fluogen luminogens due to the existence of special intramolecular charge transfer.Generally,achievement of high carrier mobility is one of the major goals in the field of organic semiconductors.To fulfill this requirement,the molecule is generally designed to have a large defined length to render expected photo/electronic properties,in which strong intermolecular ?-? stacking and dipole-dipole interactions are vital to the conducting pathways.In contrast,?-? interactions are detrimental to electroluminescence materials for organic light-emitting diodes(OLEDs)because of the formation of excimers and exciplexes in their condensed state.Since the concept of aggregation-induced emission(AIE)was pioneered by Tang et al.in 2001,a new perspective to develop functional luminescence materials has been opened up.The AIE phenomenon,different from aggregation-caused quenching(ACQ),is very important and practical owing to its inherent application potential in the solid state,including high-tech applications in optoelectronics,chemosensors,and bioimaging.Mechanoresponsive luminescence(MRL)materials have attracted considerable attentions because of their interesting applications in sensors,memory chips,and smart inks.One obvious feature of MRL materials is that their absorption and/or emission of light can be modulated by mechanical forces such as grinding,smearing and hydrostatic pressure.To date,a lot of AIE/MRL materials have been explored from the highly fluorescencent AIE molecules.However,most of the known MRL molecules give only luminescence dichromic behavior,and reports on high-contrast MRL turn-on are still rare.As one of the classical AIE cores,TPE has been widely used to construct various funcational fluorescencent materials.In the field of MRL,TPE is considered as a super star to fabricate MRL molecules.However,the achievement of high-contrast MRL turn-on from TPE based MRL compounds is not easy.Fine tuning of intermolecular interactions is of great significance on rational design for ?-conjugated molecules.Herein,we design and synthesis AIE and MRL molecules by incorporating different different heterocyclic cores and chromophore to finely tune the electronic structures of fuorescent compounds.For example,two longwavelength emission AIE molecules have been achieved by combining N-phenylcarbazole and thiophene/dicyanovinyl groups in this thesis.It is noted that a high-contrast MRL turn-on(ca.1200 folds)has been realized by destroying the layered hydrogen-bonded organic framework of symmetrical N-phenylcarbazole-based thiophene/dicyanovinyl molecule.Moreover,the combination between TPE with coumarin and phenyl/dicyanovinyl is suggested to introducing two counter-acting forces and result into a metastable "off" fluorescence,but guarantee the high contrast luminescenceon-off switching in the solid state.The details of this paper are shown as the following:Chapter 1:Research background of this thesis has been described.Chapter 2:Among the classes of organic ? systems,nitrogen-containing heterocycles are very promising building blocks in synthesizing a great number of strongly emissive materials.1,10-Phenanthroline(phen),as a type of common electron-decient group,is ofen fused with electron-rich units to construct various D-A molecules.In this chapater,a series of unsymmetric phen based aromatic heterocyclic derivatives with TPA and thiophene donors(L1-L5)and their respective neutral tricarbonyl rhenium(I)complexes(6a-6e)has been described.Comparisons between isomeric compounds L1/L2 and 6a/6b as well as L3/L4/L5 and 6c/6d/6e have been made on their 1H NMR and UV/Vis spectra,single-crystal structures and density function theory(DFT)calculations.The alterations of conjugated system of the whole molecules,originating from the introduction of 2-,3-or 3,8-substituted TPA and thiophene groups of phen,are responsible for the structural and spectral discrepancy of these structural isomers.In particular,the introduction of TPA and/or thiophen donors at 2-postion of phen(L1 and L3)leads to smaller band gaps than their respective 3-substituted isomers(L2 and L4).In addition,rhenium(I)ion complexation could slightly lower the highest occupied molecular orbital(HOMO)energy levels but significantly decrease the lowest unoccupied molecular orbital(LUMO)energy levels of the molecular system.Chapter 3:This chapter probes the mechanoresponsive luminescence(MRL)and aggregation-induced emission(AIE)properties of N-phenylcarbazole based thiophene/dicyanovinyl(T-DCV)derivatives.In bis-T-DCV planar molecule 1,a layer hydrogen-bonded organic framework(HOF)structure is formed with the assistance of multiple C-H…N and strong interlayer interactions.The formation of such a layer packing HOF structure can quench the solid fluorescent emission when aggregated as nanosuspensions,but guarantee the high-contrast luminescence on-off switching(1.2×103 fold)in the solid state.Moreover,the grinding induced destruction of HOF 1 is reflected by PXRD measurements,in which the destroy of the ? and ? rings in the planar HOF stripe and the close interlayer stacking could be observed.This work achieves the successful construction of long-wavelength emission AIE molecules(2 and 3)by introducing sufficient steric hindrance rotors to disturb the intermolecular ?-? stacking and/or dipole-dipole interactions.Chapter 4:This chapter is to explore high-contrast mechanoresponsive luminescence(MRL)turn-on materials by combining the features of the coumarin and typical aggregation-induced emission enhancement(AIEE)tetraphenyethylene groups.So fluorogen C3Ph is obtained by fusing triphenylvinyl and coumarin units,which exhibits typical AIEE characteristics with high solid-state photoluminance(PL)efficiency in amorphous state.The formation of a unique 2D hydrogen-bonded organic framework(HOF)is responsible for the crystalline-state PL quenching but guarantees the luminescence turn-on to the external stimuli.Furthermore,the reversible solid-state fluorescence on-off cycle for C3Ph can be achieved by alternate grinding and melting-solidifying.This work also offers a way to construct high-contrast MRL turn-on materials by using the HOF-involved molecules.Chapter 5:A pair of TPE-based E/Z isomers(E-TPE2PD and Z-TPE2PD)has been synthesized and separated successfully.The introduction of dicyanovinyl groups will generate different molecular polarity and help the successful separation of E/Z mixtures.At the same time,both isomers exhibit remarkable solvatochromic effects.Furthermore,reversible E/Z isomerization for each isomer is achieved,in which the isomerization speed from E to Z is quicker than that from Z to E.This pair of pure E/Z isomers exhibits obvious AIEE properties.Z-TPE2PD shows highly morphology-dependent solid-state photoluminescent properties,whose solid-state emission is red-shifted from 564 to 588 nm with the enhancement of crystalline degree together with the decrease in the emission intensity.In contrast,E-TPE2PD leads to slightly blue-shifted emission of 5 nm depending on its crystalline degree.To the best of our knowledge,the discrepancy in emissive color between TPE-based E and Z isomers is much larger than most of the reported ones.The absence and presence of ?-? stacking interactions between adjacent PD units observed in their crystal packing structures are suggested to be responsible for the distinct solid fluorescence of E and Z isomers.More interestingly,Z-TPE2PD displays blue-shifted MRL turn-on behavior when suffering grinding,while E-TPE2PD shows remarkable two-color PL nature.This work offers a synthetic strategy by introducing strong polar dicyanovinyl groups into the TPE core to increase the molecular polarity difference of E and Z isomers and facilitate their separation,which makes possible the exploration of distinguishing morphology-dependent solid-state PL properties.