In the realm of semiconductor nanomaterials, a crystal lattice heavily doped with cation/anion vacancies or ionized atomic impurities is considered to be a general prerequisite to accommodating excess free carriers that can support localized surface plasmon resonance (LSPR). Here, we demonstrate a surfactant-assisted nonaqueous route to anisotropic copper sulfide nanocrystals, selectively trapped in the covellite phase, which can exhibit intense, size-tunable LSPR at near-infrared wavelengths despite their stoichiometric, undoped structure. Experimental extinction spectra are satisfactorily reproduced by theoretical calculations performed by the discrete dipole approximation method within the framework of the Drude-Sommerfeld model. The LSPR response of the nanocrystals and its geometry dependence are interpreted as arising from the inherent metallic-like character of covellite, allowed by a significant density of lattice-constitutional valence-band free holes. As a consequence of the unique electronic properties of the nanocrystals and of their monodispersity, coherent excitation of symmetric radial breathing modes is observed for the first time in transient absorption experiments at LSPR wavelengths.

The interplay of photochromism and fluorescence was studied by attaching anthracene as chromophore to dithienylperfluorocyclopentene (1,2-bis[5-anthryl-2-methylthien-3-yl]perfluorocyclopentene, Ac-BMTFP). The blue fluorescence of the open isomer of Ac-BMTFP is suppressed by the ring-closure reaction. The spectroscopic properties and the reaction dynamics of this compound were characterized by measurements of the fluorescence yield and decay dynamics, and the quantum yields of the photochromic ring-closure and ring-opening reactions, as well as the spectra and time evolution of reaction intermediates. The data are analyzed in terms of a model potential and single-electron density matrices, which are calculated using the collective electronic oscillator (CEO) approach and the INDO/S semiempirical Hamiltonian. For the ringopening reaction, single-exponential decays with a time constant of 8 ( 0.5 ps were determined for the photoinduced bleaching and absorption transients. In contrast, because of the presence of reacting and nonreacting conformers, the dynamics measured for ring closure are more complex. Both conformers of the open isomer undergo a fast electronic-conformational relaxation on a time scale of ≈0.9 ps after excitation of the S 1 or S 3 state. Nonreacting conformers fluoresce with a distribution of lifetimes ranging from less than 100 ps to more than 400 ps. Reacting conformers reach a precursor state with a lifetime of 10 ps from which the ring-closure reaction takes place. The rates of the ring-opening and ring-closure reactions are determined as 9.5 × 10 9 and 6 × 10 10 s -1 , respectively. Rather than being a drawback, the presence of different conformers in the sample is argued to be a requirement for applications relying on efficient switching of the fluorescence.

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Superparamagnetic iron oxide nanoparticles (SPIONs) with a mixed phase composition (γ-Fe2O3)(1-x)(Fe3O4)x and sizes between 9 and 20 nm were synthesized via coprecipitation and were either left uncoated or subsequently surface-stabilized with citrate or malate anions. The sizes, morphology, surface chemistry, and magnetic properties of the nanoparticles were characterized using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, and superconducting quantum interference device measurements, respectively. Cellular uptake and intracellular distribution in normal tissue and tumor cells were verified by TEM images. X-ray-induced changes of the oxidation state and site geometries of surface iron ions of uncoated and citrate-coated SPIONs were explored by collecting Fe K-edge X-ray absorption spectroscopy data. The potential applicability of citrate- and malate-coated SPIONs as an X-ray enhancer for radiation cancer therapy was substantiated by their drastic enhancement of the concentration of reactive oxygen species (ROS) in X-ray irradiated tumor cells.

The influence of a bulky, strongly coupled substituent (benzoyl−phenyl−ethenyl, BPE) on the dynamics of the photoinduced ring-closure and ring-opening reactions of 1,2-bis[[2−methyl−thien−3−yl]]perfluorocyclopentene (BMTFP) in solution was investigated. UV/vis absorption spectroscopy in combination with chemical actinometry was employed to determine the reaction quantum yields. The relaxation and reaction dynamics were studied by transient absorption spectroscopy, exciting the S0−S2 transition of the open isomer with pump pulses at 288 nm, while 657 and 410 nm pulses were used to excite the S1 and S2 states of the closed isomer, respectively. Transient absorption spectra in the range of 350−950 nm were recorded using temporally delayed, white-light continuum probe pulses. After structural relaxation in the S1 excited state, the ring-closure reaction takes place with high quantum yield through a conical intersection. This conical intersection acts also as relaxation funnel for the S1 excited state of the closed isomer, from which it is separated by an energy barrier. The branching in the conical intersection favors the closed isomer, so that the ring-opening reaction yield is small (10-3−10-4). This yield was found to vary by a factor of 6 for different isomers obtained by rotation around the ethylene bond of the substituent.

Ž. The reaction dynamics of the photochromic ring-opening reaction of 1,2-bis 5-formyl-2-methyl-thien-3-yl perfluoro-Ž . cyclopentene CHO-BMTFP in dichloromethane solution was investigated using femtosecond transient absorption spectroscopy. The data were analyzed in terms of a model potential and single-electron density matrices, which were calculated Ž . using the collective electronic oscillator CEO approach and the INDOrS semiempirical Hamiltonian. The S -S and 0 1 S -S transitions of the closed isomer were resonantly excited using 120 fs pump pulses at 610 and 410 nm, respectively. A 0 2 temporally delayed white light continuum probe pulse monitors the decay of the S or S state as well as the recovery of the 1 2 S state. Within the first picosecond after excitation, CHO-BMTFP was observed to undergo a fast structural relaxation 0 along the S potential energy surface into a minimum constituting a precursor of the ring-opening process. The rather long 1 lifetime of the precursor, t s 13 ps, was consistent with the calculated potential barrier in front of the conical intersection 2 with the S potential energy surface, which may arise from stabilization of the nearly planar closed isomer by an efficiently 0 delocalized p-electron system. q

This paper reports spectroscopic investigations of the chromophore terrylene embedded in a matrix of crystalline p-terphenyl. While this system is particularly well suited for single molecule spectroscopy, little is known about the guest site configuration of terrylene. To shed some light on this issue, we employed absorption and fluorescence spectroscopy and compared the experimental data to the results of theoretical calculations. Based on this comparison we suggest a substitution scheme which is in agreement with all the spectroscopic evidence. The dispersed fluorescence spectra of single molecules in the wings of the inhomogeneous distribution deviate significantly from the bulk spectra. This observation is discussed in terms of a host-induced change of the structure and a possible C13 isotopic substitution of the chromophores. Finally we investigated the dynamic host–guest interactions via the temperature-dependent shift and broadening of single molecule excitation lines and found these processes dominated by coupling to characteristic pseudolocal phonon modes of the host, although chromophores in the wings of the inhomogeneous distribution exhibit additional contributions which we attribute to thermal matrix expansion.

Absorption and emission spectra of monomers and dimers of [tetramethoxytetrakis(octyloxy)phthalocyaninato]silicon have been measured as a function of solvent and concentration. In contrast to the monomer, the fluorescence of the dimer is shifted to lower energy by about 4000 cm -1 , and the emission quantum yield is reduced by a factor of 10 -3 . The spectroscopic data are analyzed in the strong coupling limit of dimer models and lead to an excitation exchange interaction term of 1770 cm -1 and an evaluation of the excited state lifetime of ca. 24 ps. This fast decay is dominated by nonradiative processes. The admixture of ion pair configurations is suggested to provide an efficient coupling to the environment and channel of decay of the exited state energy. Small contributions of such configurations to the ground state are also invoked to explain the marked changes in the absorption spectra as a function of environment (solvent) and concentration (aggregation).