Two-photon Dye Research Articles

Superradiance and lasing properties of new two-photon absorption dye DEASPS

Pumped by picosecond pulses from a Nd:YAG laser, a new lasing dye, trans-4-[4′-(N,N-diethylamino)styryl]-N-methyl pyridinium methyl sulfate (abbreviated to DEASPS), shows both intense superradiance and strong lasing properties in benzyl alcohol solution. By using streak camera systems, the superradiance and lasing can be distinguished both spectrally and temporally. It has been found that the peak wavelength of lasing is at 620 nm with a red-shift of about 12 nm to the superradiance wavelength. The lasing pulse shows an oscillatory effect that it is not found in the superradiance pulse. The fluorescence lifetime is 529 ± 40 ps and the effective molecular two-photon absorption is (1.25 ± 0.1) × 10−48 cm4 ·s·photon −1, measured using a nonlinear transmittance method. This dye shows effective optical limiting of the pumping wavelength.

Electrically switchable reflection holograms formed using two-photon photopolymerization

Two-photon holographic photopolymerization was used to form switchable Bragg gratings composed of layers of phase-separated liquid-crystal (LC) domains interspersed with cured, crosslinked polymer. These holographic polymer-dispersed liquid crystals form a periodic structure which diffracts red light due to nanostructured planes ∼250 nm in spacing. These structures were formed by interfering two 90-fs pulses coherently upon a reactive syrup consisting of acrylate monomer, liquid crystal, and a two-photon dye. The large two-photon cross-section allows excitation of the two-photon dye that results in electron transfer between this dye and the monomer. Diffraction efficiencies of approximately 10% were obtained, which can be modulated using an electric field applied across the film. Switching speeds below 1 ms were observed due in part to the small size of the LC domains.

A New Approach to Design Light Emitting Devices Using Electroactive Dyes

ABSTRACTOrganic electroluminescence (EL) single layer devices using electroactive dyes incorporated in poly-vinylcarbazole (PVK) were fabricated. The molecular structures of the two-photon dyes are the generic D-π-A;, D-π-D, and A-π-A;, structural motif, composed of a diphenylamine donor (D), a distyrylfluorene π-bridge, and an oxadiazole acceptor (A). A single layer type of EL device of ITO/PVK:DYE/Ca/Al was fabricated. The light emission peak and the threshold of the electroluminescence emission depend on the structure and concentration of the dye. The EL intensity increases with the dye concentration and it was found that as the voltage is increased the brightness increases and reaches a value 498 cd/m2 at an applied voltage of 25 V for the D-π-A; dye. We present a physical explanation of this observed behavior and show that this has significant impact on the design of light emitting devices using these organic dyes.

Linear and Nonlinear Optical Properties of an Erbium Two-Photon Dye Salt

The optical properties of erbium tri-4-{[4-(2-{4-[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-phenyl}-vinyl)-phenyl]-phenyl-amino}-benzoate, viz., an erbium two-photon dye salt, were investigated in THF solutions. Using the corresponding two-photon dye monomer acid as a reference material, we observed that the photoluminescence of the erbium two-photon dye salt was quenched significantly while nonlinear absorption for infrared nanosecond excitation was enhanced compared to the monomeric form. On the other hand, femtosecond Z-scan measurements suggest the same two-photon absorption coefficient for the dye in both forms. A possible explanation is that the presence of erbium enhances the intersystem crossing rate and that the nonlinear absorption effect must be due to two-photon absorption and subsequent triplet−triplet excited-state absorption for nanosecond pulsed excitation. Our analysis of the nonlinear absorption (power limiting) data suggests that the intersystem crossing rate is 3 orders of magnitu...

Silica Nanobubbles Containing an Organic Dye in a Multilayered Organic/Inorganic Heterostructure with Enhanced Luminescence

We report the preparation, luminescent properties, and bioimaging applications of a novel zinc sulfide (core)-two-photon dye−silica (shell) multilayered heterostructure. The method utilizes reverse micelles synthesis involving multistep reactions as a result of which composite nanoparticles having different sizes and morphology can be obtained. The size of these composite nanoparticles is typically 15−30 nm. An increase in the luminescence intensity (∼70 times higher) and in fluorescence lifetime is observed for the dye encapsulated within the silica nanobubble. Photobleaching results indicate that the dye is truly encapsulated and the silica shell provides a barrier to penetration of oxygen, thereby making the dye more photostable. The application of these particles as nanoprobes for bioimaging of cells using two-photon laser scanning microscopy is also presented.

High-density three-dimensional optical data storage in a stacked compact disk format with two-photon writing and single photon readout

Using a polymer block doped with a highly efficient two-photon dye, we have achieved a high density data storage with gray-scale control in multiple planes as stacked compact disks at a separation of 10 μm. The absorption and fluorescence of the dye at the written spot shift to a longer wavelength, permitting an easy fluorescence mode readout with a linear excitation using an inexpensive laser source. The storage capacity in this case is estimated to be 1012 bits/cm3.

Highly Active Two-Photon Dyes: Design, Synthesis, and Characterization toward Application

A series of compounds with systematically varied molecular structures which exhibit very large effective two-photon cross sections has been synthesized and characterized in solution using a nonlinear transmission technique. The general structure of these compounds can be categorized into two basic structural families: acceptor/donor/donor/acceptor and donor/bridge/acceptor. This study attempts to determine certain molecular structure/effective two-photon absorption relationships by careful characterization and as a function of systematically varied changes in the organic structure of the dye molecules. Such information can be useful in the design of more efficient two-photon dyes for imaging and power-limiting applications. The results of the study indicate that with the incorporation of certain combinations of structural elements, dyes can be synthesized which have greatly increased effective cross sections as high as 152.5 × 10-48 cm4 s/photon molecule in benzene solution at 800 nm using 8 ns pulses. T...

Fluorescence Study of DNA–Dye Complexes Using One-Photon and Two-Photon Picosecond Excitation

Preliminary results of investigation of one-photon- and two-photon-induced fluorescence of acridine orange (AO), epirubicin (ER), hypericin (HYP), and ethidium bromide (EB) in complexes with DNA are presented. A spectrofluorometer based on a picosecond Nd:YAG laser was used for investigations of two-photon (1064-nm, 1-mJ, 40-ps) and one-photon (532- and 355-nm) dye excitation. The spectra of two-photon-induced fluorescence of dyes and their complexes with DNA as well as the kinetics of dyes' fluorescence intensification during their interactions with DNA in dependence on the biomacromolecule concentration were obtained. The intensities of AO, HYP, and EB fluorescence were increased 2.4, 3.2, and 8 times, respectively, after binding with DNA at two-photon excitation, while at one-photon excitation the corresponding values were 2.5, 3.7, and 10 times. The difference in fluorescence enhancement during DNA–dye complex formation at linear and nonlinear excitation may possibly be associated with the fact that the cross sections of one-photon and two-photon absorption, in general, change unequally during the binding of dyes to organic molecules and bathocromic shift of the electronic transitions. It was shown that the peak of AO fluorescence shifted to a longer wavelength on 10 nm after two-photon excitation at 1064 nm in comparison with one-photon excitation at 532 nm.

Enhanced SHG and two-photon dye luminescence from metal particle surfaces

Enhanced surface phenomena have received considerable attention in recent years, e.g., surface enhanced Raman scattering and enhanced luminescence. Here we report enhanced surface second harmonic generation (SHG)1 from metal island films of continuously varying thickness on sapphire substrates and two-photon excitation of adsorbed dyes.