| Organic π-conjugated materials have attracted more and more attentions due to excellent photoelectric properties and extensive application prospect.In addition,earlier studies suggested that there were important relationships between molecular packing modes and luminous properties.For example,morst π-conjugated materials with H-aggregate dramatically decreased the luminescence quantum yield in the solid state(films and crystal).Because the inter dipole interaction along their long axis induced the nonradiative decay of exciton.The molecular packing modes have also a great effect on their ability to transport charges.X-aggregate with small intermolecular π-overlap showing the high photoluminescence efficiency,however,was deficient for charge transport.Recently,knowledge of the role of molecular packing in controlling luminous properties of π-conjugated materials have been utilized for exploring stimuli-responsive material,where the fine-tune molecular packing modes were achieved by an external stimulus including pressure,heat and solvent vapor.At present,however,the number of organic dyes exhibiting piezofluorochromism was still limited,due to lack of full understanding of the piezochromic mechanisms at the molecular-level.Moreover,the fluorescence could return to the original color by exposure to solvent vapor and high temperature(more than 40 ℃).And those noxious solvents were rarely used in our daily life,which limited the potential for practical application.Thus,It was of great significance and challenge to investgate the molecular packing modes and intermolecular interactions for obtaining the practical stimuli-responsive material.A series of novel organic π-conjugated materials containing aromatic amine were desighed and synthesized.Then the relationship among external factor(heating,pressure and solvent vapor),molecular packing modes and luminescent properties was systematically investigated.In Chapter 2,two blue-emitting oligomers,namely FDPA1 and FDPA2 containing 9,10-diphenylanthracene core end-capped with triphenylamine-substituted fluorene have been designed and synthesized by Suzuki couping and Friedel-Crafts reaction.The spiro-configuration end-capping groups imparted two compounds with pronounced morphological stability(Tg>185 ℃,Td>420 ℃),hight Φf(Φf>0.62)and excellent hole injection ability(EHOMO>-5.27 eV).Scanning electron microscope(SEM)and X-ray diffraction(XRD)revealed that the two oligomers formed excellent amorphous films and possessed good morphologicalstability after annealing.The results indicated two oligomers can be used as emitting and hole-transporting materials in OLED.The device utilizing FDPA1 as emitting layer achieved pure blue luminescence at 447 nm with turn-on voltage of 3.5 V and maximal brightness of 3400 cd/m2 at voltage of 9.6 V.In Chapter 3,intramolecular charge-transfer cyanostilbene derivatives CNS-4 with aggregation-induced emission enhancement(AIEE)activity and piezofluorochromic behaviors are desighed and prepared by Knoevenagel and Suzuki reactions.With the increase of the volume fractions of water(fw)in the THF/water from 0 to 50%,the emission profile is continuously red-shifted as well as reducing its quantum yield.However,the fluorescence intensity abruptly increases in the solvent mixture with fw>50%,achieving an intensity maximum at water content of 90%under the same processing conditions.By the fluorescence spectroscopy and Transmission electron microscopy(TEM)analysises,two factors may result in the varieties of the emission bands:solvatochromism and aggregation effect.In addition,the emission maximum blue-shift of nanoparticle suspension from the DMF-H2O mixture to the THF-H2O mixture seems to be attributed to the change of nanoparticle morphology from amorphous to crystalline.In Chapter 4,The organic luminophoric dye TPA-CO indicated the effect of aggregation-caused quenching(ACQ)in aggregate state with quantum yields(Φf)of 0.4%.The white powders were changed into relatively strong blue-emissive solids(Φf=12.3%,λem = 472 nm)after grinding by a spatula.Interestingly,these ground powders could revert to the original solids upon heating and sovent vapor treatments.The piezochromism can be understood as a phase transition process by powder X-ray diffractometry,SEM and time-resolved fluorescence spectrofluorometer analysises.Furethermore,the fluorescence was switched between bright and dark states repeatedly by simple grinding-heating or grinding-fuming cycles.Finally,we proposed that loose intermolecular packing with low energy of crystal lattice inducing piezochromic luminescence resulted from the twisted conformation and weak intermolecular interactions.In Chapter 5,Two isomers(TPA-CNa and TPA-CNb)consisting of cyano group and twisted triphenylamine were effortlessly synthetized by Knoevenagel condensation and C-N coupling reaction.The fluorescent colours of two isomers were sky-blue for TPA-CNa and green for TPA-CNb with Φf of 44.9%and 7.7%,respectively.The desired compound TPA-CNa showed multistimuli-responsive fluorescence switching behavior.This sample was changed into weaker green-emissive solid(Φf=21.2%)through grinding treatment.The ground powder could recover its original state upon heating at about 60℃ over 2 min.In addition,the fluorescent changing from green to blue was also achieved by exposure to vapor of various organic solvents.Among them,medicinal alcohol(75%)and Chinese liquor(56°)were harmless and regularly used in our daily life.The changes of molecular stacking pattern were investigated by single crystal XRD analyses,powder X-ray diffractometry,SEM and time-resolved fluorescence spectrofluorometer.The crystal-to-crystal phase transition driven by external stimuli was responsible for the piezochromic fluorescence modulation.Importantly,by comparing molecular stacking of two isomers,it was found that loose intermolecular packing was the determining factor in affecting piezofluorochromic activity.In Chapter 6,TPA-MeO and TPA-HeO showed piezo-induced and revisable solid sate phase transformation properties which are accompanied by the switehes between the different fluorescent color and luminous efficiency.The crystals with Φf less than 0.1%were changed into relatively strong green-emissive solids(Φf=24.1%)after grinding by a spatula.Moreover,the ground cystals could recover its original state upon heating by exposure to vapor of alcohol.TPA-HeO xerogel also indicated piezochromic luminescence.The piezochromism can be understood as a phase transition process by powder X-ray diffractometry,SEM,and time-resolved fluorescence spectroscopy. |
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