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1.
Dent Mater ; 37(7): 1183-1192, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-33994202

RESUMO

OBJECTIVE: The aim of the study was to investigate the effects of methacrylate-functionalized proanthocyanidins (MAPAs) on dentin collagen's bio-stabilization against enzymatic degradation and crosslinking capability. METHODS: Three MAPAs were synthesized via varying methacrylate (MA) to proanthocyanidins (PA) feeding ratios of 1:2, 1:1, and 2:1 to obtain MAPA-1, MAPA-2, and MAPA-3, respectively. The three MAPAs were structurally characterized by proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopic methods. 5-µm-thick dentin films were microtomed from dentin slabs of third molars. Following demineralization, films or slabs were treated with 1% MAPAs or PA in ethanol for 30 s. Collagen bio-stabilization against enzymatic degradation was analyzed by weight loss (WL) and hydroxyproline release (HYP) of films, as well as scanning electron microscopy (SEM) on dentin slabs. Crosslinking capacity and interactions of MAPAs with collagen were investigated by FTIR. Data were analyzed by ANOVA and Tukey's test (α = 0.05%). RESULTS: MA:PA feeding ratios affected MAPAs' chemical structures which in turn led to different collagen stabilization efficacy against degradation and varied collagen crosslinking capabilities. Higher collagen stabilization efficacy was detected using MAPA-1 (WL 10.52%; HYP 13.53 µg/mg) and MAPA-2 (WL 5.99%; HYP 11.02 µg/mg), which was comparable to that using PA (WL 8.79%; HYP 13.17 µg/mg) (p > 0.05), while a lower collagen stability occurred in MAPA-3 (WL 38.48%; HYP 29.49 µg/mg), indicating excessive MA-functionalization would compromise its stabilization efficacy. In comparison, complete digestion was detected for untreated collagen (WL 100%; HYP 102.76 µg/mg). The above results were consistent with collagen crosslinking efficacy of the three MAPAs revealed by SEM and FTIR. SIGNIFICANCE: A new class of novel polymerizable collagen cross-linkers MAPAs was synthesized and shown that, when appropriate MA:PA ratios were applied, the resulting MAPAs could render high collagen stability and the ability to copolymerize with resin monomers, overcoming the drawbacks of PA. These new polymerizable crosslinkers, when included in adhesives, could lead to long-lasting dentin bonding.


Assuntos
Colágeno , Colagem Dentária , Proantocianidinas , Dentina , Adesivos Dentinários , Metacrilatos , Resistência à Tração
2.
Dent Mater ; 37(7): 1193-1201, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-33965250

RESUMO

OBJECTIVE: The aim of the study was to investigate the effects of a novel polymerizable collagen cross-linker methacrylate-functionalized proanthocyanidins (MAPA) on the polymerization, microhardness and leaching of a HEMA-based experimental dental adhesive system. METHODS: Three MAPAs were synthesized using different methacrylate (MA) to proanthocyanidins (PA) feeding ratios of 1:2, 1:1, and 2:1 to obtain MAPA-1, MAPA-2, and MAPA-3, respectively. The resulting three MAPAs and PA were added to an experimental adhesive formulated with HEMA and a tri-component photoinitiator system (0.5 wt% CQ/EDMAB/DPIHP) at 1%, 5% and 10% MAPA or PA concentrations (wt%). The adhesive polymerization kinetics was measured continuously in real-time for 10 min using a Fourier-transform infrared spectroscopy (FTIR) with an attenuated total reflectance (ATR) accessory. Degree of conversion (DC) and Vickers microhardness (MH) of cured adhesives were measured at 72 h post-cure. The leaching of cured adhesives in DI water was monitored using UV-vis spectrophotometer. Statistical analysis was performed using one-way and two-way ANOVA, Tukey's (p < 0.05). RESULTS: The adhesive formulations with 1%, 5% and 10% MAPAs-1, -2, -3 all generated higher rate of polymerization and 10-min DC than the formulations with PA at the same concentrations. At 72 h post-cure, the adhesive formulation with 5% MAPA-2 exhibited significantly higher DC (99.40%) and more than doubled MH (18.93) values than the formulation with 5% PA (DC = 89.47%, MH = 8.41) and the control (DC = 95.46%, MH = 9.33). Moreover, the cured adhesive with 5% MAPA-2 demonstrated significantly reduced PA leaching in comparison with cured adhesive with 5% PA. SIGNIFICANCE: Synthesized MAPA is a novel class of polymerizable collagen cross-linker that not only stabilizes dentin collagen via its PA component, but also improves polymerization, mechanical properties and stability of HEMA-based adhesives via its MA component. By inheriting the benefit while overcoming the drawback of PA, MAPA offers a revolutionary solution for improved bond-strength and longevity of dental restorations.


Assuntos
Metacrilatos , Proantocianidinas , Bis-Fenol A-Glicidil Metacrilato , Colágeno , Cimentos Dentários , Cura Luminosa de Adesivos Dentários , Teste de Materiais , Fotoiniciadores Dentários , Polimerização
3.
Ying Yong Sheng Tai Xue Bao ; 31(8): 2687-2698, 2020 Aug.
Artigo em Chinês | MEDLINE | ID: mdl-34494792

RESUMO

Green space ecological network is important for improving the fragmentation of regional ecological space, biodiversity loss, imbalance of supply and demand in ecosystem services, and ensuring regional ecology. With Dongting Lake region as an example, the ecological sources were evaluated and identified, and basic ecological resistance of grid element was calculated from the perspectives of comprehensive ecosystem service function evaluation, potential biodiversity comprehensive index evaluation and morphological spatial pattern analysis with the support of 3S technology. We corrected the basic ecological resistance by night light index, used the minimum cumulative resistance model to identify ecological corridors, and constructed a weighted evaluation model, eva-luated the degree of aggregation and dispersion of the sources, as well as the contribution of ecological connection of the corridors. Furthermore, we compared and evaluated the structural characteristic index of the integrated networks, the potential "source sink" networks and the planning networks. The results showed that the spatial distribution of the sources was uneven, with forest land, shrubland and wetland acounting for 95.9% of the total area. The Dongting Lake wetland located in the middle of the region was at high ecological risk. The closer the source was to the center of the ecological network system and the smaller the average minimum cumulative resistance was to other sources, the stronger the advantages of aggregation and dispersion. The denser the distribution of medium and high ecological quality sources was around the high ecological quality sources, the higher the aggregation and dispersion. The closer the corridor was to the high ecological quality sources, the greater contribution of ecological connection. Forest land, shrubland, especially river played an important role in connecting natural ecosystem and human social system. The "source-sink" planning greenways formed a supplement to the "source-sink" potential ecological corridors. Compared with the "source-sink" potential network, the α, ß, γ and ρ index of the integrated network was increased by 123.1%, 25.8%, 26.2% and 74.6% respectively. Compared with the "source-sink" planning network, the α, ß, γ and ρ index was increased by 190.0%, 31.1%, 32.5% and 114.6% respectively. The results could provide reference for the construction of green space ecological network and planning of land use in Dongting Lake region.


Assuntos
Conservação dos Recursos Naturais , Ecossistema , Biodiversidade , China , Ecologia , Humanos , Lagos , Parques Recreativos
4.
Biomater Sci ; 7(12): 5247-5257, 2019 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-31602445

RESUMO

Fibrous chitin dressing (FCD) prepared from a NaOH-urea aqueous solution of chitin via a physical process was used to study its effect on wound healing using a full-thickness cutaneous wound model in rats and mice. It was demonstrated that wounds in rats covered with the FCD showed faster collagen (especially type I collagen) growth and speedier healing than those with Gauze (12 days versus 16 days). The ability of FCD to promote wound healing was also observed on wild-type (WT) mice. For MyD88-knockout mice, however, FCD displayed no beneficial but an adverse effect on wound healing: the healing time for wounds treated with FCD was even longer than those treated with gauze. Importantly, in vivo studies indicated that FCD-treated mice, compared to gauze-treated ones, exhibited markedly higher expressions of MyD88, IKBα, TGF-ß, P-TßR II, TßR II and P-Smad2/3 in wild-type mice. For MyD88 knockout mice, however, the expressions of those molecules were inhibited and lowered in FCD-treated ones than those treated with gauze. In vitro studies confirmed that chitin increased the expression of TGF-ß, P-TßRII and P-Smad2/3 while the expressions of those molecules were significantly inhibited with CD14 antibody (p < 0.05). These results indicated that FCD accelerated wound healing through a MyD88-dependent pathway, followed by a TGF-ß/Smad pathway. This work not only demonstrated the superior wound healing effect of chitin-derived dressing, but also provided for the first time the underlying molecular mechanism, further establishing chitin as an important biomedical material for potential clinical applications.


Assuntos
Bandagens , Materiais Biocompatíveis/química , Materiais Biocompatíveis/farmacologia , Quitina/química , Quitina/farmacologia , Cicatrização/efeitos dos fármacos , Animais , Proliferação de Células/efeitos dos fármacos , Colágeno Tipo I/metabolismo , Fibroblastos/citologia , Fibroblastos/efeitos dos fármacos , Fibroblastos/metabolismo , Regulação da Expressão Gênica/efeitos dos fármacos , Masculino , Camundongos , Fator 88 de Diferenciação Mieloide/metabolismo , Ratos , Ratos Sprague-Dawley , Receptores de Fatores de Crescimento do Endotélio Vascular/metabolismo , Proteínas Smad/metabolismo , Hidróxido de Sódio/química , Fator de Crescimento Transformador beta/metabolismo , Ureia/química , Fator A de Crescimento do Endotélio Vascular/metabolismo , Água/química
5.
Wei Sheng Yan Jiu ; 45(6): 921-926, 2016 Nov.
Artigo em Chinês | MEDLINE | ID: mdl-29903074

RESUMO

OBJECTIVE: To describe the statue of growth and development among infants and young children aged 6-23 months in poor rural areas of Hunan Province. METHODS: A total of 15 248 rural infants and young children aged 6-23 months in 54 poor counties of Wuling Mountains and Luoxiao Mountains in Hunan Province were selected by Probability-Proportional-to-Size Sampling( PPS) between 2009 and 2015. Participants' length and weight were tested, WHZ, WAZ, HAZ and BMI Z score were calculated according to The WHO Child Growth Standards, and describe the rate of wasting, underweight, stunting and low BMI, and the physical growth level of children were evaluated according to the WHO standards. RESULTS: The average weight of girls aged 6-23 months in poor rural areas of Hunan Province were 9. 17 kg, lower than boys which were 9. 79 kg. The average length of girls aged 6-23 months were 75. 53 cm, lower than boys which were 77. 19 cm. The average BMI of girls aged 6-23 months were15. 96, lower than boys which were 16. 40( P < 0. 05). The curve of weight-for-length Z scores and weight-for-age Z scores and length-for-age Z scores of infants and young children aged 6-23 months were lower than the WHO standards( P < 0. 05). The rate of wasting, underweight, stunting and low BMI of infants and young children aged 6-23 months were 3. 9%, 5. 1%, 7. 2% and 3. 9%, and boys were higher than girls in the rate of underweight and stunting, the rate of underweight and stunting were increased with the growth of age( P < 0. 05). CONCLUSION: The problem of growth and development of infants and young children aged 6-23 months in poor rural areas of Hunan Province are serious, and there are lower than the WHO standards. To improve the nutrition and health of infants and young children in poor rural areas, the ability of child health care and the feeding knowledge of caregivers are need to be improved.


Assuntos
Transtornos do Crescimento/epidemiologia , Estado Nutricional , População Rural , Peso Corporal , China/epidemiologia , Feminino , Transtornos do Crescimento/etnologia , Humanos , Lactente , Masculino , Prevalência
6.
ACS Appl Mater Interfaces ; 7(18): 9372-84, 2015 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-25915005

RESUMO

Charge carrier mobility and its optimization play a critical role in the development of cutting-edge organic electronic and optoelectronic devices. Even though space-charge-limited current (SCLC) hole mobilities as high as 1.4 cm(2) V(-1) s(-1) have been reported for microscopically sized highly ordered liquid-crystalline conjugated small molecules, the SCLC hole mobility of device-sized thin films of conjugated polymers is still much lower, ranging from 10(-6) to 10(-3) cm(2) V(-1) s(-1). Herein, we report the synthesis, characterizations, and thin-film SCLC mobility of three discotic conjugated polymers, INDT-TT, INDT-BT, and INDT-NDT. Optical studies indicate that polymer INDT-NDT adopts a folded conformation in solutions of good or poor solvents, whereas polymer INDT-TT stays as random monomeric chains in good solvents and interchain aggregates in poor solvents. INDT-BT polymer chains, however, stay as foldamers in dilute solutions of good solvents but interchain aggregates in concentrated solutions or poor solvents. Circular dichroism spectroscopy provides clear evidence for the helical folding of INDT-NDT in solutions. Thin films spin-coated from 1,2-dichlorobenzene solutions of the polymers show SCLC hole mobility of 2.20 × 10(-6), 8.79 × 10(-5), and 2.77 × 10(-2) cm(2) V(-1) s(-1) for INDT-TT, INDT-BT, and INDT-NDT, respectively. HRTEM and powder XRD measurements show that INDT-NDT pristine thin films contain nanocrystalline domains, whereas the INDT-TT and INDT-BT films are amorphous. Thin films of INDT-NDT:PC71BM blends show increased crystallinity and further improved SCLC hole mobility up to 1.29 × 10(-1) cm(2) V(-1) s(-1), one of the highest SCLC mobility values ever recorded on solution-processed organic semiconducting thin films. The persistent folding conformation of INDT-NDT is believed to be responsible for the high crystallinity of its thin films and its high SCLC mobilities.

7.
Pharm Res ; 31(3): 706-19, 2014 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24072263

RESUMO

PURPOSE: Rapamycin has demonstrated potent anti-tumor activity in preclinical and clinical studies. However, the clinical development of its formulations was hampered due to its poor solubility and undesirable distribution in vivo. Chemical modification of rapamycin presents an opportunity for overcoming the obstacles and improving its therapeutic index. The objective of this study is to develop a drug-polymer conjugate to increase the solubility and cellular uptake of rapamycin. METHODS: We developed the rapamycin-polymer conjugate using a novel, linear, poly(ethylene glycol) (PEG) based multiblock copolymer. Cytotoxicity and cellular uptake of the rapamycin-polymer conjugate were evaluated in various cancer cells. RESULTS: The rapamycin-polymer conjugate provides enhanced solubility in water compared with free rapamycin and shows profound activity against a panel of human cancer cell lines. The rapamycin-polymer conjugate also presents high drug loading capacity (wt% ~ 26%) when GlyGlyGly is used as a linker. Cellular uptake of the conjugate was confirmed by confocal microscopic examination of PC-3 cells that were cultured in the presence of FITC-labled polymer (FITC-polymer). CONCLUSION: This study suggests that the rapamycin-polymer conjugate is a novel anti-cancer agent that may provide an attractive strategy for treatment of a wide variety of tumors.


Assuntos
Antibióticos Antineoplásicos/administração & dosagem , Portadores de Fármacos/química , Polietilenoglicóis/química , Polímeros/química , Sirolimo/administração & dosagem , Antibióticos Antineoplásicos/química , Antibióticos Antineoplásicos/farmacocinética , Antibióticos Antineoplásicos/farmacologia , Linhagem Celular Tumoral , Humanos , Neoplasias/tratamento farmacológico , Sirolimo/química , Sirolimo/farmacocinética , Sirolimo/farmacologia , Solubilidade
8.
J Am Chem Soc ; 135(44): 16490-6, 2013 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-24094119

RESUMO

Donor-acceptor nanofibril composites have been fabricated, and the dependence of their photocurrent response on the structure and morphology of the donor part has been systematically investigated. The nanofibril composites were composed of template nanofibers, assembled from an electron acceptor molecule, perylene tetracarboxylic diimide (PTCDI), onto which (through drop-casting) various electron donor molecules (D1-D4) were coated. The donor molecules have the same π-conjugated core, but different side groups. Due to the different side groups, the four donor molecules showed distinctly different propensity for intermolecular aggregation, with D1-D3 forming segregated phases, while D4 prefers homogeneous molecular distribution within the film. It was found that the nanofibril composites with D4 exhibit the highest photocurrent, whereas those with aggregation-prone D1-D3 exhibited much lower photocurrent under the same illumination condition. Solvent annealing is found to further enhance the aggregation of D1-D3 but facilitate more uniform molecular distribution of D4 molecules. As a result, the photocurrent response of PTCDI fibers coated with D1-D3 decreased after vapor annealing, whereas those coated with D4 further increased. The detrimental effect of the aggregation of donor molecules on the PTCDI fiber is likely due to the enhanced local electrical field built up by the high charge density around the aggregate-nanofiber interface, which hinders the charge separation of the photogenerated electron-hole pair. The results reported in this study give further insight into the molecular structural effect on photoconductivity of hybrid materials, particularly those based on donor-acceptor composites or interfaces, and provide new molecular design rules and material processing guidelines to achieve high photoconductivity.

10.
J Phys Chem A ; 115(9): 1579-92, 2011 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-21309552

RESUMO

A donor-acceptor charge transfer system based on two discotic mesogens has been synthesized. The donor is either a triphenylene (POG0) or a triphenylene-based conjugated dendron (POG1), while the acceptor is a perylene diimide (PDI) core. The donors are covalently linked to the bay positions of the PDI core through an ether linkage. In chloroform, due to the short donor-acceptor distance and the matching frontier orbital levels, photoinduced charge transfer from either the donor excitation or the acceptor excitation are both thermodynamically and kinetically favored, resulting in efficient quenching of both donor and acceptor fluorescence. In a less polar solvent, hexane, while charge transfer is still the dominant mechanism for decay of the excited electronic state of POG1, photoinduced charge transfer is no longer energetically favorable for POG0 when the acceptor PDI core is excited, making the PDI core of POG0 weakly fluorescent in chloroform but strongly so in hexane. In solid film, POG0 is highly aggregated through both PDI-PDI and triphenylene-triphenylene homotopic stacking. POG1, on the other hand, aggregates through triphenylene dendrons with limited PDI-PDI core stacking, presumably due to the steric hindrance caused by bulky triphenylene moieties which block the access to the PDI core. The efficient photoinduced charge transfer, coupled with the homotopic stacking that forms separated electron-transporting PDI-stacked columns and hole transporting triphenylene-stacked columns, suggests that the reported donor-acceptor systems based on dual-discotic mesogens are potentially new efficient photovoltaic materials.


Assuntos
Crisenos/química , Dendrímeros/química , Dendrímeros/síntese química , Imidas/química , Imidas/síntese química , Fenômenos Ópticos , Perileno/análogos & derivados , Transporte de Elétrons , Perileno/síntese química , Perileno/química
11.
Chem Commun (Camb) ; 46(43): 8171-3, 2010 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-20922261

RESUMO

The first iodinated cyclopentadienone was isolated and its structure was confirmed by single crystal X-ray analysis. Based on this intermediate, the first direct C-C bond formation on cyclopentadienone ring was achieved. The photo induced intramolecular charge transfer of alkynylated cyclopentadienones was evaluated by solvent polarity effect on their electronic absorption spectra.

12.
Science ; 326(5950): 263-7, 2009 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-19815771

RESUMO

Adaptive laser pulse shaping has enabled impressive control over photophysical processes in complex molecules. However, the optimal pulse shape that emerges rarely offers straightforward insight into the excited-state properties being manipulated. We have shown that the emission quantum yield of a donor-acceptor macromolecule (a phenylene ethynylene dendrimer tethered to perylene) can be enhanced by 15% through iterative phase modulation of the excitation pulse. Furthermore, by analyzing the pulse optimization process and optimal pulse features, we successfully isolated the dominant elements underlying the control mechanism. We demonstrated that a step function in the spectral phase directs the postexcitation dynamics of the donor moiety, thus characterizing the coherent nature of the donor excited state. An accompanying pump-probe experiment implicates a 2+1 photon control pathway, in which the optimal pulse promotes a delayed excitation to a second excited state through favorable quantum interference.

13.
J Biomed Mater Res A ; 90(4): 1120-7, 2009 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-18671261

RESUMO

This study evaluated different initiator systems in self-etching model adhesives, in which camphorquinone (CQ) or [3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-2-hydroxylpropy] trimethylammonium chloride (QTX) was employed as a photoinitiator (dye). N-phenylglycine (NPG), ethyl 4-dimethylaminobenzoate (4E) or 2-(dimethylamino) ethyl methacrylate (DMAEMA) was used as the coinitiator (CI). The role of diphenyliodonium hexafluorophosphate (DPIHP) in the polymerization process was also studied. The concentrations of dye, CI, and DPIHP in model adhesives were all maintained at 0.022 mmol per gram monomer. The model adhesive contained two monomers: (bis[2-(methacryloyloxy)ethyl] phosphate) (2MP) and 2-hydroxyethyl methacrylate (HEMA) whose mass ratio was 1:1, thus representing an acidic and hydrophilic formulation. The polymerization rate and the degree of conversion (DC) of the model adhesives with 5, 15, or 25% water content were determined using FTIR/ATR with a time-based spectrum analysis. The results indicated that with CQ as the photoinitiator, 4E appeared to be the most efficient CI, whereas the CQ-DMAEMA combination led to very low radical generation efficiency (DC < 5%). DPIHP exhibited little effect on the polymerization process. With QTX as the photoinitiator, however, DPIHP played an essential role. Without DPIHP, all three QTX-CI systems failed to initiate polymerization (DC < 5%). The QTX-DPIHP combination, on the other hand, was found to be a viable initiator system. The above results provide the critical information for the development of self-etching adhesive systems.


Assuntos
Cimentos Dentários/síntese química , Processos Fotoquímicos , Ácidos , Compostos de Bifenilo/química , Corantes , Metacrilatos/química , Oniocompostos/química , Água
14.
Photosynth Res ; 87(1): 115-31, 2006 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-16408143

RESUMO

We review the synthesis and photophysical properties of light harvesting phenylacetylene dendrimers with unsymmetrical branching. We describe the steady state and time dependent experiments that are used to characterize energy transfer properties in the conjugated dendrimers. Finally, we describe investigations of the unsymmetrical phenylacetylene dendrimers as potential materials for applications in fluorescence-based sensors, and for non-linear optics.


Assuntos
Materiais Biomiméticos/química , Materiais Biomiméticos/efeitos da radiação , Dendrímeros/química , Dendrímeros/efeitos da radiação , Luz , Fotoquímica , Fatores de Tempo
16.
Inorg Chem ; 44(22): 7711-3, 2005 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-16241119

RESUMO

The first chiral molecular hybrids based on covalently linked polyoxometalate clusters and enantiopure 1,1'-binaphthyl units have been prepared. Their structures have been confirmed by (1)H NMR, FTIR, and ESI-MS measurements. Such hybrids show moderate chiroptical behavior in solutions, and Cotton effects are observed up to 450 nm, indicating chiral extension from the binaphthyl core to the cluster-containing pi-conjugated arms.


Assuntos
Naftalenos/química , Compostos de Tungstênio/química , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Naftalenos/metabolismo , Espectrometria de Massas por Ionização por Electrospray , Espectroscopia de Infravermelho com Transformada de Fourier , Estereoisomerismo , Compostos de Tungstênio/metabolismo
17.
J Phys Chem B ; 109(28): 13553-60, 2005 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-16852696

RESUMO

We have applied the fluorescence upconversion technique to explore the electronic excitation energy transfer in unsymmetrical phenylene ethynylene dendrimers. Steady-state emission spectra show that the energy transfer from the dendrons to the core is highly efficient. Ultrafast time-resolved fluorescence measurements are performed at various excitation wavelengths to explore the possibility of assigning absorption band structures to exciton localizations. We propose a kinetic model to describe the time-resolved data. Independent of the excitation wavelength, a typical rise-time value of 500 fs is measured for the fluorescence in the dendrimer without an energy trap, indicating initial delocalized excitation. While absorption is into delocalized exciton states, emission occurs from localized states. When an energy trap such as perylene is introduced on the dendrimer, varying the excitation wavelength yields different energy-transfer rates, and the excitation energy migrates to the trap through two channels. The interaction energy between the dendrimer backbone and the trap is estimated to be 75 cm(-1). This value is small compared to the vibronic bandwidth of the dendrimer, indicating that the monodendrons and the energy trap are weakly coupled.

18.
J Fluoresc ; 14(1): 105-12, 2004 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-15622869

RESUMO

We report the absorption, photoluminescence (PL), and time-dependent PL of thin films of conjugated phenylacetylene monodendrons at both room temperature and at cryogenic temperature. We find that the PL properties of the monodendron thin films are significantly different from their fluorescence in dilute solution due to the presence of interactions between monodendrons in the thin film. These interactions lead to aggregate species in the thin films, which result in broader PL spectra and lower PL quantum yields than for monodendrons in dilute solution. Evidence for excimer-like aggregates in the monodendron thin films is found from time-resolved PL spectra.

19.
Inorg Chem ; 43(20): 6408-13, 2004 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-15446891

RESUMO

Two new charge-transfer hybrids with one or two ferrocenyl units covalently attached to a hexamolybdate cluster through an extended pi-conjugated bridge have been prepared using Pd-catalyzed coupling reactions on monoiodo- or diiodo-functionalized cluster substrates in over 60% yields. These hybrids have been characterized by (1)H NMR, FTIR, electrospray ionization mass spectrometry, and X-ray diffraction. The electronic spectra of these hybrids show a broad absorption tail extending beyond 550 nm, indicating the existence of charge-transfer transition from the ferrocenyl donor to the cluster acceptor. The observation of the clear charge-transfer transition indicates the contribution of charge-transfer resonance to the ground state in both 2a and 2b even though the donor-acceptor separation distance of 11.29 A is rather long, signaling a through-bond charge-transfer nature made possible by the organic pi-conjugated bridge. Cyclic voltammetry studies reveal a one-electron oxidation wave and a one-electron reduction wave for the hybrid with one ferrocenyl unit. For the one with two ferrocenyl units, a lower reduction potential and a two-electron oxidation wave are observed, indicating negligible electronic interactions between the two ferrocenyl units.


Assuntos
Compostos Ferrosos/química , Molibdênio/química , Compostos Organometálicos/síntese química , Catálise , Cristalografia por Raios X , Metalocenos , Modelos Moleculares , Conformação Molecular , Compostos Organometálicos/química , Platina/química
20.
Angew Chem Int Ed Engl ; 43(8): 930-5, 2004 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-14966875

RESUMO

Hybrid materials based on covalently linked inorganic polyoxometalates (POMs) and organic species containing a delocalized pi system have drawn increasing attention. These hybrids, traditionally prepared by cluster assembly approaches that lack predictability and controllability, can now be synthesized through common organic reactions by using organically functionalized POM clusters as building blocks. This minireview highlights some of the most recent advances on a particular type of hybrids where the organic and inorganic components are connected by an imido linkage.

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