| As an emerging class of organic-inorganic hybrid carbon nanomaterial,carbon dots(CDs)have garnered vast interest for their versatile photoluminescence performance,outstanding photo-stability and low toxicity,since their first discovery in 2004.To date,researches concerning the preparation and photoluminescence(PL)applications of CDs have achieved remarkable progress.In particular,CDs have shown promising prospects in a wide range of potential applications such as imaging,sensing,graphic patterning,illumination and so on.However,rational control of the structural regularity,which fundamentally determines the optical performance of CDs,is still not fully achieved due to the limitation of existing synthesis strategies and methods.Such limitation have restrained the further applications of CDs in the field of PL,to a certain degree.With the continuous deepening of relative research,practical applications have put forward higher requirements to the photo-physical performance of CDs.Specifically,the improvement of CDs are most-desired in two major aspects: For one thing,the basic optical performance of CDs—including excitation/emission performance in the longwavelength region,overall brightness and color purity—requires further optimization.For the other,smart responsive features should be introduced into the CDs materials in order to endow them with stimuli-responsive performances,toward certain chemicals compounds and/or specific photonic/acoustic/thermic/electronic signals.Since the optical properties of CDs are determined by their structural character,the requirement of improving the photo-physical performance fundamentally demands rational synthesis of CDs with predictable structure.Considering the general speculated polymerizing-carbonizing pathway in the bottom-up synthesis of CDs,herein we have designed three different photoluminescent CDs materials with advanced optical performance and smart stimuli-responding properties.By referring to the coupling and polymerizing principles of unsatruarated hexatomic rings and amine compounds,CDs with target structure and predicted functionalities were prepared from specific molecular precursors.In this thesis,the reaction between unsatuarated hexatomic rings and amines were rationally applied for the construction of CDs for the following reasons:(1)According to previous reports,the intentional use of precursors with unsatuarated hexatomic rings tends to introduce photoluminescent structure with large conjugation,which clearly benefited the luminescent efficiency of CDs,especially for materials with longer excitation/emission wavelength.(2)The use of amines in CDs synthesis not only improves the dispersion stability of the materials,but also introduced nitrogen as heteroatom dopants,which tends to improve the opotical performance of CDs.Specifically,nitrogen doping not only enhances the luminescence efficiency of CDs,but also promotes their phosphorescent emission with longer lifetime.(3)Compounds with unsatuarated hexatomic rings,such as aromatic amines and benzoquinone,are capable of reacting with amines under mild condition,which fundamentally allows rational construction of CDs materials with improved optical performance and desirable smart responsive character.The details of each design are given as followed:(1)By referring to the synthesis of polyaniline,we adopted 2,4-diaminotoluene as the precursor to synthesis a novel type of polymer carbon dots,polyaniline quantum dots(PAQDs)with internalized polyaniline backbones.The as-prepared PAQDs showed bright green PL under the irradiation of both UV light and 800 nm near infrared femtosecond pulsed laser,with a quantum yield(QY)of 32.5%.Importantly,the builtin polyaniline structure endowed the PAQDs with a unique proton doping/dedoping feature,allowing its sensitive response towards environmental p H.The variation of structure and optical characters(absorption and emission)of PAQDs during the reversible doping-dedoping process were further confirmed by spectroscopy methods.Finally,taking advantage of the excellent water solubility and low toxicity of this material,we successfully applied PAQDs as a p H indicating probe for the highlight labelling of acidic bio-targets both in vitro and in vivo.(2)Using a highly conjugated aromatic amine molecule 4,4',4''-Triaminotriphenylamine(TAPA)as the precursor,we successfully synthesized a carbon quantum dots(CQDs)material,T-CQDs,with advanced structural regularity under a mild solvothermal synthetic condition.The as-prepared T-CQDs featured a red emission(615 nm)with high brightness(QY>80%)and excellent color purity(fullwidth at half-maximum < 30 nm),which in combination represented one of the best optical performance of red CQDs reported so far,while being comparable to commercial inorganic quantum dots.What's more,T-CQDs was capable of upconversional emission under the excitation of a NIR-II(1100 nm)pulsed laser,which provided additional advantage of improved signal depth in bio-imaging applications.Based on the advanced optical performance of this material,series of bio-imaging experiments were successfully performed using T-CQDs as a PL probe.Specifically,the NIR-II-light-driven two-photon fluorescence of T-CQDs had further enabled the imaging of thick samples such as tissues or living animals with improved depth.(3)A CDs-based afterglow composite material with smart stimuli-responsive features was design and fabricated by cooperating N,O-functionalized CDs with a polymer host.Synthesized from benzoquinone and ethylenediamine,the CDs were rich in lone-pair electron structures that promoted the spin-orbit coupling and facilitated its triplet states.By blending with hydrogen-bonded polymer host like polyacrylamide(PAM)or Polyvinyl Pyrrolidone(PVP),the phosphorescent long afterglow of CDs were further enabled.Specifically,reversible photo-induced volatile afterglow with optical memory feature was realized in the CDs/PVP composite.The afterglow memory effect of the CDs/PVP composite was mediated by an in situ photodynamic oxygen removal process,which allowed precise afterglow patterning on the film by irradiation.Through optimization,the final product featured ultra-long PL lifetime(582 ms),high on-off switching ratio(50:1 by intensity and 3932:1 by lifetime),good reversibility(>70% remained intensity after 40 times on/off cycling),thermally sensitive retention time(from minutes to days)and high patterning resolution(>1280 dpi).Utilizing the unique character of this CDs composite material,we proposed an editable smart tag that can be processed by ink-free printing and applied for graphic encryption.On that basis,the potential application of this smart tag for thermal history indication in cold chain logistics was further demonstrated. |
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