Preparation And Study Of Photo-responding Supramolecular Materials

Supramolecular chemistry, defined as “chemistry beyond the molecule”, was studied on theassembled entities of higher complexity that resulted from the association of two or more moleculesheld together through the non-covalent-bond (secondary bond). It is an important method to explorenovel functional supramolecular complexes by constructing functional small molecules to the polymersby non-covalent-bond interactions. This method is simple and the structure of supramolecular complexis easy to control. More importantly, the weak interactions and reversibility of non-covalent bondsendow the supramolecular materials with some special properties. This dissertation mainly consists oftwo parts: The first part focuses on the photosensitive ionic complexes including azobenzene by theionic self-assembly technique. The relationship between the azobenzene structure and materialproperties was discussed. Anisotropic fluorescence emission materials were prepared by thecooperative orientation of fluorescent molecules during the orientation process of azobenzene. Thesecond part researches on the hydrogen-bond supramolecular electrospun fibers, including fluorescentelectrospun fibers and colorimetric response electrospun fibers. The detailed contents are shown asfollows:(1) A series of photoresponding ionic complexes was prepared by the ionic self-assembly (ISA) ofsodium polyacrylate (PANa) and azobenzene chromophores (RAZO) bearing different terminal groups(-CN,-OMe,-N(CH3)2, and-CF3), which are designated as PACNAZO, PAMAZO, PANDAZO, andPACFAZO, respectively.1H NMR, IR and EDS show that the ionic self-assembly of PANa and RAZOis according to the stoichiometric1:1charge ratio. The ionic complexes are stable up to165°C。 Thelamellar microstructures of the complexes are confirmed by X-ray diffraction. By comparing the Braggspacing “d” of the complexes with the calculated lengths of the side chains, two kinds of layeredarchitectures are proposed. The ionic complexes with an electron-donating terminal substituent (σp-R <0) form an interdigitated lamellar structure with full overlap of the side chains, while the complexeswith an electron-withdrawing terminal substituent (σp-R>0) form an interdigitated packing structurewith partial overlap of the side chains. The PARAZO films can be oriented under the irradiation with 355nm linear pulsed laser. The orientation direction is perpendicular to the laser polarization. Thein-plane orientation order parameter (S) of PANDAZO film is up to0.59. For the weak absorption at355nm, the photoinduced orientation of PACFAZO film is not obvious. Finally, the photoinducedbirefringence properties of the complex films are investigated. The PANDAZO film shows extremelyhigh birefringence (n=0.365) by using488nm continuous laser as the pump light. The other ioniccomplexes have no obvious photoinduced birefringence for the weak absorption at488nm. Therefore,a continuous laser with short wavelength (405nm) is used as the pump light. The complex films ofPACNAZO and PAMAZO produce certain birefringence. The results show that the wavelength of thepump light is closely related to the orientation behavior of the ionic complexes containing azobenzene.This provides a theoretical guidance to design novel photosensitive materials.(2) Based on the design of the materials which contain a photoinduced orientation unit and thefluorescent unit, a series of fluorescent ionic complexes (PMmNn) are prepared based on ionicself-assembly of azobenzene unit (MAZO) and stilbene unit (Nstil) with sodium polyacrylate (PANa)according to the1:1charge ratio, in which the ratio of Nstil unit to MAZO unit is m: n.1H NMR, IRand UV-vis spectra confirm that the ionic complexes are composed of MAZO unit, Nstil unit andPANa main chain, which also confirm that the MAZO unit and Nstil unit attached to PANa backboneaccording to the initial calculated proportion. The ionic complexes exhibit high thermal stability andsmectic liquid crystalline behavior. The long-range lamellar microstructures are also confirmed bysmall angle X-ray scattering (SAXS). And layer spacing (d) of the complexes increases with theincrease of the content of the fluorescent unit. Both the MAZO unit and Nstil unit are oriented underthe irradiation with linear polarization pulsed laser. And the orientation direction is perpendicular to thelaser polarization. Polarized UV-vis spectra of the oriented PMmNn films indicate that the orientationof fluorescent unit is driven by azobenzene unit. The oriented PMmNn films exhibit anisotropicfluorescence emission. The fluorescent dichroic Rexis up to4.6. Moreover, the in-plane orderparameter S, fluorescent intensity I and dichroic Rexof the PMmNn films increase with the decreasingthe content of Nstil unit in the films.(3) The fluorescent supramolecular electrospun fibers PSVP(ST)xcontaining stilbene are prepared by electrospinning from the DMF solution of stilbene unit (ST) and polystyrene-co-poly(4-vinylpyridine)(PS-co-P4VP), where stilbene unit with hydroxy group is the hydrogen-bond donor while thehydrogen-bond acceptor is PS-co-P4VP. The electrospun conditions are optimized from workingvoltage, working distance, the concentration of PS-co-P4VP and ST. Working voltage is15kV.Working distance is20cm. The electrospun temperature is40°C. The concentration of PS-co-P4VP is120mg mL-1. The hydrogen bond between the ST unit and PS-co-P4VP is confirmed by attenuatedtotal reflectance (ATR) FT-IR spectra. The supramolecular complexes show strong fluorescenceemission in DMF solution or their electrospun fibers. The hydrogen bond between the ST unit andPS-co-P4VP accelerate fluorescence emission of ST molecule in DMF solution. The fluorescence ofthe electrospun fibers is also investigated. The red shift is observed in the fiber with respect to that inDMF solution due to the dimer emission in the electrospun fibers. Furthermore, the fluorescenceintensity of the electrospun fibers increases with decreasing the content of ST in the fibers. At last, theuniaxially oriented PSVP (ST)0.04fluorescent fiber is prepared by using an aluminium U-shaped groovewith gap of1cm as receptor.(4) A series of polydiacetylene acid (PDA)-embedded supramolecular electrospun fibers areprepared and applied as colorimetric sensor of detection of temperature, organic amines and theirvapors. The PSVP(DA)xsupramolecular electrospun fiber is first prepared by electrospinning the DMFsolution of10,12-pentacosadiynoic acid (DA) and polystyrene-co-poly(4-vinylprydine)(PS-co-P4VP)(“x” in the abbreviation represented the molar ratio of DA molecular to the pyridyl group inPS-co-P4VP). The uniform-dimeter and continuous fibers are obtained when the concentration ofPS-co-P4VP is100mg mL-1. The hydrogen bond between the carboxyl groups of DA monomers andthe pyridyl groups in PS-co-P4VP is confirmed by ATR FT-IR spectra. The self-assembly of DAmonomers occurs during the evaporation of solvent in the process of electrospinning for the attractiveforce between the DA monomers (i.e. hydrophobic interaction and π-π stacking interaction). Theassembled DA monomers in fibres are further polymerized to form PDA with alternating ene-yne mainchain under the254nm UV light irradiation. The color of the fiber mats charges from white to blue.The blue color of the fibre mat becomes deeper gradually with the content of DA monomer increasing. After UV-irradiation and following annealing at90°C, no change in the morphology of the electrospunfibres is found though the color of fibre mats presented white-blue-red transition. The hydrogen bondsbetween PDA and PS-co-P4VP are not destroyed after these treatments. The colorimetric response ofthe electrospun fibers to temperature is first investigated. Take PSVP(PDA)0.12as an example, the colorchange from blue-purple-red is observed while heating the fiber mats from room temperature to90°C.Colorimetric response (CR) value is used to evaluate the degree of converting from the blue phase intored phase, which can be calculated by UV-vis spectra. The relationship between CR value and thetemperature is discussed. The colorimetric response of the supramolecular fiber mats to organic amineor their vapors is also investigated. The color change from blue to red is observed when the fiber matsexposed to100ppb concentration organic amine vapors. The selectivity of the colorimetric sensor isinvestigated. No color change is observed while exposure to common organic solvents and acidic gases.These results indicate that the PDA-embedded supramolecular fiber mats are high sensitive andselective sensors for the detection of temperature, organic amine and their vapors by simple colortransition.