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Carbon dots (CDots) are small carbon nanoparticles with effective surface passivation accomplished mostly via organic functionalization. In this study, the largely amorphous carbon nanoparticles were copolymerized with N-vinylcarbazole in microwave-assisted radical reactions. The copolymers thus formed are structurally equivalent to the individual carbon nanoparticles each surface-functionalized by multiple poly-(N-vinylcarbazole) (PVK) segments, thus denoted as PVK-CDots. Their electronic transitions and photoexcited state properties, including especially the characteristic excitation wavelength dependencies of fluorescence parameters, were found to be essentially the same as those commonly observed in CDots of small organic molecules for surface functionalization. The PVK-CDots were dispersed in neat PVK for polymeric nanocomposite films free from any other foreign materials. The optical absorptions and fluorescence emission properties of PVK-CDots in the solid-state film matrix environment were found to be little changed from those in solution. The significance of the findings and implications to various uses of these nanomaterials in optoelectronics and related fields are highlighted and discussed. [ABSTRACT FROM AUTHOR]

A systematic investigation of the absorption and emission properties of a series of C60 derivatives with mono- and multiple-functionalized fullerene cages is presented. The fluorescence lifetimes of the C60 derivatives were all between 1 ns and 3 ns.

Fullerene molecules were found to undergo efficient photochemical reactions with tertiary amines to produce complex mixtures of addition products. The separation and identification of several monoadducts from photochemical reactions of C60 with triethylamine under various experimental conditions were conducted. According to molecular spectroscopic results, the photoaddition of triethylamine to C60 is initiated through photoinduced electron transfer between the excited singlet C60 and the amine, similar to photochemical reactions of common aromatic compounds with tertiary amines. However, the reaction products with fullerene were completely different.

Research was conducted to examine the strong optical limiting of silver-containing nanocrystalline particles in stable suspensions. A versatile approach for the preparation of a series of polymer-protected metal and metal sulfide nanoparticles, which was based on the expansion of supercritical fluid solution into a liquid solution, was developed. Results reveal that optical limiting characteristics are unique to the silver-containing nanocrystalline particles.

A study was conducted relating to research on the electronic transitions and excited state properties of fullerenes and especially [60]fullerene (C60). The study reports a systematic spectroscopic investigation of a series of C60 derivatives with different cage functionalizations. Among other results, it was found that both fluorescence quantum yields and lifetimes are somewhat similar for the different classes of C60 derivatives.

A facile method for photochemically preparing high molecular weight polyfullerenes has been developed. The method involves subjecting polyfullerenes to a room-temperature solution under oxygen-free conditions. The polyfullerenes and the clusters from which polymers were prepared exhibited comparable sizes. The potential use of polyfullerenes in molecular conduction, nonlinear optics and hydrogen storage was examined.

The fluorescence quenching of polyaromatic molecules by carbon tetrabromide (CBr4) is studied. Specifically, the fluorescence lifetimes of 9,10-bis(phenylethynyl)anthracene (BPEA) in supercritical carbon dioxide (CO2) was estimated as a function of CBr4 densities via time-correlated, single-photon counting. The results confirmed the enhancement of bimolecular reactions leading to fluorescence quenching in supercritical CO2 at near-critical densities. The results suggest a solute-solute clustering mechanism from higher local quencher concentration.

A chemometrics spectral method helps determine pure absorption and fluorescence spectra of ground state charge transfer complexes and exciplexes of C60 and C70 with N, N-diethylaniline (DEA) and N,N-dimethylaniline (DMA). Solvents exhibit strong influence on exciplex emission, and both dynamic and static process participate in the quenching of monomer fluorescence. A mechanism of prompt and delayed monomer emissions explains the observation of dual fluorescence for C60/C70-DEA/DMA in hexane.

Analyses performed in near-critical liquid ethane, CO2 and their mixtures with hexane, established at room temperature, fluorescence spectra and quantum yields for tetraphenylethylene (TPE). The delayed fluorescence spectrum of TPE is obtained. The twisted excited state is zwitterionic in nature.

The characteristics of the twisted excited state of tetraphenylethylene in supercitical fluids are studied. Picosecond transient absorption measurements are performed on unpurified tetraphenylethylene with an Nd:YAG laser acting as the excitation source. Tetrahydrofuran amd n-hexane are used as received. Results reveal that the twisted excited state lifetime of tetraphenylethylene in supercritical fluid-cosolvent mixtures is very sensitive to changes of medium properties.

The photophysical properties of permethylhexasilane (Si6Me14) was determined using ultraviolet spectroscopy and Si6Me14 was found to be different from other longer oligosilanes. However, its fluorescence is not what is expected from an extrapolation from longer chains. It is proposed that the lowest singlet state nature changes between Si10Me22 and Si6Me14. It also favors one of the three possible tentative assignments for the emitting state of Si6Me14. Moreover, thetemperature-dependence of the Si6Me14 fluorescence quantum yield suggests the existence of a thermally activated radiationless decay channel.

The equilibrium observed between the locally excited and the twisted intramolecular charge-transfer states of p-(dimethylamino)benzonitrile (DMABN) and ethyl p-(dimethylamino)benzoate (DMAEB) could serve as molecular probes for analyzing supercritical fluid and mixture reactions. The emissions of both DMABN and DMAEB were monitored using fluorescence spectroscopy. Moreover, characterization of the supercritical reactions involved principal component analysis-self modeling and nonlinear least squares method.

Fluorescence measurements were conducted on all-trans-1,6-diphenyl-1,3,5-hexatriene in methylcyclohexane. Resolution of the compound's spectra featured a mixture of 2(super 1) A(sub g)/1(super 1) B(sub u) and red-shifted fluorescence spectra from all-s-trans and s-cis conformers, respectively. Principal-component analysis with self-modeling calculations confirmed the temperature dependence of the compound's s-cis conformers.

The solute-solvent interactions of p-(N,N-dimethylamino)benzonitrile and ethyl p-(N,N-dimethylamino)benzoate in supercritical trifluomethane, carbon dioxide and ethane solutions were examined using absorption and emission spectral measurements. The results indicated that varying densities affected the spectral shifts exhibited by the two compounds. The spectral shifts were were further categorized in three intermolecular interactions characterized as gaslike, near-critical and liquidlike densities.

The development of carbon materials as highly efficient and durable substrates for surface-enhanced Raman scattering (SERS) is of great importance for realizing practical application of molecular sensing through Raman spectroscopy. In this report, we demonstrate the fabrication, by low-temperature pyrolysis, of high-quality, iron–nitrogen-doped carbon nanosheets and nanorods from spin-coated poly-(4-vinylpyridine) (P4VP) polymer thin films and electrospun polymer nanofibers, respectively. As P4VP chains have functional pyridine rings available to bind with metal precursor ions through favorable interactions, iron (Fe) atoms can be incorporated into the carbon nanostructures with the aid of Fe-(II) acetate during the synthesis. The incorporation of a metal salt can decrease the thermal stability of pyridinic groups so that the pyrolysis produces carbon nanostructures with high degree of graphitization and with iron- and nitrogen-doped species. The codopants in these carbon nanostructures introduce surface dipole moments, affect the DOS of valence bands, and decrease the work function. The electronic structure of carbon nanomaterials can be finely tuned to enable the vibronic coupling of the conduction band and valence band states of carbon nanostructures with the excited and ground states of the probed molecules of Rhodamine 6G and crystal violet. The vibronic coupling enables a superior enhancement in SERS with the detection limit concentration being as low as 10–7 M and the maximum enhancement factor being 3.8 × 104 through a charge transfer (CT) process. The polymer-templated carbon nanostructures offer great promise for the implementation of this system in a next-generation SERS substrate for molecular sensing. [ABSTRACT FROM AUTHOR]

The derivative porphyrin tetrakis-21H, 23H-prophine (THPP) selectively interacts with and solubilizes semiconducting single-walled porphyrin tetrakis(SWNT), resulting in the 'extraction' of most of the semiconducting SWNTs from the starting purified nanotube sample.

Research demonstrates the functionalization or carbon nanotubes by amidation and esterification of the bound carboxylic acids and characterization of the modified nanotubes by solution-based echniques. Data discuss the solubility, dispersion, and optical properties of the functionalized carbon nanotubes and their deployment in the fabrication of different types of nanomaterials.