H.Z. Wang

Photophysical properties and TPA optical limiting of two new organic compounds

The emission and optical limiting properties of two new organic compounds have been experimentally investigated. Pumping by picosecond and nanosecond lasers, respectively, these two compounds possess strong two-photon absorption and optical limiting effects. The results of time-resolved fluorescence of them in DMF solvent at the different concentrations and small quantum yields indicate that the non-radiation process and reabsorption result in the low emission efficiency of these new molecules with large two-photon absorption (TPA) cross-sections.

Two-photon absorption spectra of new organic compounds

Abstract Two-photon absorption (TPA) spectra of three organic compounds have been directly measured by an approach of using tunable laser from an optical parameter amplifier as an excitation source. The output intensity of the optical parameter amplifier can cover a broad spectral range 400–2000 nm, and the same intensity in the whole spectral range can be easily adjusted. Therefore, the measurement based on this method is direct and reliable. The experimental results show that the profiles of the TPA spectra are quite similar to those of the linear absorption spectra. All of these compounds exhibit large TPA cross-section in a broad spectral range from 750 to 1100 nm.

Spectral properties and effective upconverted lasing of new organic molecules

Abstract A series of new organic molecules with high efficiency for two-photon-pumped lasing have been synthesized in this work. Ultrafast spectroscopy demonstrates very fast emission dynamics in this kind of compound, which is an important characteristic for their application. It results in an efficiency of upconverted amplified spontaneous emission (ASE) up to 12.6% at the pumping of a picosecond laser.

The coordination dimer from ZnTPP and M(m-PyOMP) (MH2 or Cu): spectroscopic properties and crystal structure

Abstract The coordination dimer, which was formed by the linkage of meso -5-(pyridinyl)-octamethylporphyrin (H 2 ( m -PyOMP)) to (5,10,15,20-tetraphenylporphyrinato) zinc(II) (ZnTPP), was confirmed by proton NMR spectroscopy and fluorescence spectrophotometry. The coordinated diporphyrin demonstrated interporphyrin singlet state energy transfer with a rate contant of ∼1.1 × 10 10 s −1 . The dimer that was composed of (5,10,15,20-tetraphenylporphyrinato)zinc(II) and [ meso -5-(pyridinyl)octamethylporphyrinato] copper(II) crystallized in the monoclinic space group P2 1 n with a = 11.666(4), b = 28.116(6), c = 20.02(1), A, β = 106.97(5)° and Z = 4. For 5275 observed reflections, the refinement yielded R = 0.075. The presently-described non-covalent approach to donor-acceptor assembly provides a novel and useful approach to mimic the natural photosynthetic process.

Photophysical properties of dodecaphenylporphyrins with different substituents

Abstract The absorption and fluorescence properties of a series of substituted dodecaphenylporphrins in dichloromethane are reported. The structures calculated using molecular mechanics reveal that there exist similar conformations independent of the substituents at meso-phenyl rings. The electronic effect of the peripheral substituents is responsible for the spectral red shift and the reduced lifetimes.

Excitation energy-transfer processes between two trimers in C-phycocyanin hexamer from the cyanobacterium Anabaena variabilis. Investigation by group theory and time-resolved fluorescence spectroscopy

Abstract We have employed group theory and picosecond time-resolved fluorescence isotropy and anisotropy spectroscopy methods to explore the excitation transfers within an isolated C-phycocyanin (C-PC) hexamer (αβ) 6 PC L 27 RC , situated at the end of the rod proximal to the core of the pycobilisome (PBS) in the cyanobacterium Anabaena variabilis . The group-theory results imply that excitation energy transfer between two trimers occurs between the lowest exciton level of each trimer. The excitation energy-transfer process might occur at a rate of 10–20 ps, and it may be described by an exciton hopping-like Forster transfer mechanism. Dynamic components of 45–50 ps are assigned to the excitation transfer from β 155 -PCB chromophores to the exciton states of dimers, which consist of two neighbouring monomers of the same trimer in an isolated C-PC hexamer.

Time-resolved excitation density dependent fluorescence of R-phycoerythrin single crystal

Abstract The fluorescence kinetics of a new single crystal, R-phycoerythrin (R-PE), has been studied by picosecond laser spectroscopy. An excitonic band, which is much more narrow than that of the molecular fluorescnece, is observed. At high pump density, superradiance of excitons in the bulk pure single crystal is recorded. The experimental results of fluorescence kinetics and exciton superradiance of R-PE crystal demonstrate that exciton energy transfer is natural, effective and rapid. It is concluded that excitons play an important role in energy transfer in the antennae of photosynthetic systems.

Time-Resolved Fluorescence of Aggregated Chlorophylls

Most of chlorophylls exist as aggregated chlorophyll-protein complexes in thylakoid membranes of plant chloroplasts, in which chlorophyll-chlorophyll interaction and processes such as charge separation and recombination contribute much to their physical, chemical and biological properties. In order to study effects of chlorophyll-chlorophyll molecular interaction and processes such as charge separation and recombination in vivo, an in vitro model system of aggregated chlorophylls is an approach, and it has therefore received much attention in the past1–4. In this communication, picosecond time-resolved fluorescence of aggregated chlorophylls, together with fluorescence of aggregated chlorophylls during deaggregation, is studied.