The Self-Assembly Behavior Of Poss-Pdis Under Concentrated Solution And Construction Of Its Polymer Base Microspheres With High Fluorescence Efficiency

Perylene diimide dye (PDI) has a planar structure with two imines of perylene ring and a strong π-conjugation, which have very strong photonics and fluorescence properties. Those favorable properities lead to the potential applications on field effect transistor, molecular electronics, light trapping, solar cells and light emitting diodes. In dilute solution, perylene diimide has high fluorescence quantum yield (near100%) while in concentrated state, especially in solid state, the fluorescence is highly quenched due to the attraction of dipole-dipole interaction and π-π stacking between molecules.A series of perylene derivatives with nanoparticle POSS substituent at imide position were designed and synthesized by researchers in our group, and their self-assembly behavior has been investigated. It was found that the nanoparticle POSS can improve solubility of PDIs, morever, it can also give stereo-hindrance to π-π stacking and make POSS-PDIs form aggregators with discontinuous π-π interaction by using dimmer as motif. Thus, crystal with high fluorescence efficiency (48%) was obtained.In this thesis, the self-assembly behavior of POSS-PDIs, including Isobutyl-POSS-PDI-POSS (isobutyl-PPP), isobutyl-POSS-PDI-OH (isobutyl-PPOH), isooctyl-POSS-PDI-POSS (isooctyl-PPP) and isooctyl-POSS-PDI-OH (isooctyl-PPOH), during spin-coating formation from high-concentration solution were focused on. And We proposed to make a "solid-soluton" of polymer/POSS-PDIs and devoted to prepare fluorescent micorspheres with high fluorescence efficiency by means of adjusting formation process, self-assembly of POSS-PDIs and the interaction between POSS-PDIs and polymer matrix. Thus, fluorescent PHBV/isobutyl-PPP, PHBV/isobutyl-PPOH and PS/isobutyl-PPP miscrospheres were prepared by electrospraying. Here. PS was chosen as matrix because we want to examine the effect of benzene rings in PS molecular chain, which may have π-π interaction with PDI. on the self-assembly behavior and fluorescent emission. The main results are as followings:1. The absorption and emission characteristics of POSS-PDIs are all concentration-dependent. As the concentration increased, the molecules turn from non-aggregated state to aggregated state, and most of the aggregated state is dimer. As concentration increasing, the emission peaks show red-shift and its intensity decrease under higher concentation. π-π interaction and hydrogen bonding is the force, which make POSS-PDIs aggregate.2. After spin-coating at high concentration, films were formed by those POSS-PDIs and show characteristic absorbing bands of PDIs in their absorption spectra, but the red shift is observed from their fluorescence emission spectra compared with those of their precursor solution. SEM and AFM results show belt-like or acicular crystalline particles are present on the surfaces of the films. It should be noted that the films prepared by isobutyl-PPOH and isooctyl-PPOH form forest-shape protuberance structure, and the big protuberances show Maltase black cross and red and green petal shape under fluorescence-polarizaton microscope. It is proposed that the differences of self-assembly at high-concentration solution for POSS-PDI-POSS and POSS-PDI-OH are from the presence of hydrogen bonding of hydroxyl groups.3. The particles prepared by electro-spraying with long receiving distance were spherical-shape with hollowed structure, thus particles were changed to be hemocyte-shape with hollowed structure and smooth surface by shorten the receiving distance. The UV-Vis spectra of PHBV/isobutyl-PPP particles prepared by electrospraying show the characteristic absorbing bands of PDI, but the UV-vis bands were wider than the solution-state absorption bands and showed red shift at the same time. The fluorescent emission spectra of PHBV/isobutyl-PPP particles only showed a wide emission band at622nm (the same as emission peak of crystal) and a shoulder peak at560nm, which is different from those at the solution state. With the increase of POSS-PDIs solution concentration, the intensity of shoulder peak decreases and the emission band at622nm showed red shift. The absolute fluorescence quantum efficiency of "dry jet spraying" microspheres ranged from20%to30%while only15%to25%efficiency were obtained for "dry-wet jet spraying" microspheres, which is caused by the effect of poor solvent alcohol.4. The UV-Vis spectra of all PHBV/isobutyl-PPOH particles showed PDI characteristic absorbing bands whether those were prepared by "dry jet spraying" and "dry-wet jet spraying", but the bands were more wider than the solution-state absorption bands. Their fluorescent emission spectra also showed obvious solution-like emission characteristic peaks except for the red shift of emission peak position at increased concentrations. The emission peaks of micorspheres prepared by "dry jet sprying" were528-530nm,570-572nm,622-654nm, respectively, while those peaks were changed to be528-531nm,572-574nm,627-662nm, respectively for "dry-wet jet spraying" method. The absolute fluorescence quantum efficiency of "dry jet spraying" microspheres ranged from11%to29%while "dry-wet jet spraying" microspheres ranged from5%to20%which is lower than "dry jet spraying" microspheres. Besides, PHBV/isobutyl-PPOH microspheres showed more red shift and lower absolute fluorescence quantum efficiency compared with PHBV/isobutyl-PPP microspheres.5. The PS/isobutyl-PPP particles prepared by electrospraying with long receiving distance showed excellent optical properties. Both UV-Vis absorption spectra and fluorescent spectra showed PDI characteristic absorbing bands and emission bands. Moreover, the shapes of the emission bands were quite similar to that at dilute solution. It confirms that the PS/isobutyl-PPP is quite the "solid-solution" model. The absolute fluorescence quantum efficiency of the particles with different concentrations ranged from55.39%to99.73%. With the concentration increase, all three emission peaks of particles at solid state showed red shift comparing with those at solution. It is supposed that the π interaction between PS matrix and PDI caused their differences.