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A novel π-conjugated dendritic nanosized chromophore, 1,3,5-tris(7,12-bis(2-{4-[2-(7-diphenylamino-9,9-dibutyl-9H-fluoren-2-yl)-vinyl]-phenyl}-vinyl)-5,5 ,10,10,15,15-hexabutyl-10,15-dihydro-5H-diindeno[1,2-a;1‘,2‘-c]fluoren-2-yl)-benzene (3), was synthesized and characterized, together with its corresponding one- and three-branched units. Two-photon absorption (TPA) spectra for these chromophores were measured by the nonlinear transmission spectral technique which utilizes a femtosecond white-light continuum. The TPA peak value for the dendritic chromophore is 5.47 × 10^-20 cm⁴/GW, 15.6 times larger than that for the one-branched dipolar chromophore (0.35 × 10^-20 cm⁴/GW), [9,9-dibutyl-7-(2-{4-[2-(9,9-dibutyl-9H-fluoren-2-yl)-vinyl]-phenyl}-vinyl)-9H-fluoren-2-yl]-diphenylamine (1). The three-branched chromophore, 2,7,12-tris(2-{4-[2-(9,9-dibutyl-7-diphenylamino-9H-fluoren-2-yl)-vinyl]-phenyl}-vinyl)-5,5,10,10,15,15-hexabutyl-10,15-dihydro-5H-diindeno[1,2-a;1‘,2‘-c]fluorene (2) has a TPA peak value of 2.28 × 10^-20 cm⁴/GW, 6.5 times as large as that for compound 1. The enhanced two-photon absorption found in these two multibranched chromophores is attributed to the fact that the dendritic or the three-branched chromophore has both an extended π-conjugated system and an increased intramolecular charge redistribution compared to the one-branched chromophore. With use of comparable structure unit based concentrations, the two-photon excited (TPE) fluorescence intensity for this dendritic chromophore (0.0033 M solution) was found to be enhanced by a factor of 2.9 compared to that for chromophore 1 (0.02 M solution), which would offer a major advantage in TPE fluorescence related applications.

III−V semiconductor quantum dots are of considerable interest as their applications cover a broad spectrum, from optoelectronic to biomedical technology. For them to be of practical value, there is a need for a method that provides rapid and scalable production of highly monodispersed nanoparticles. This paper reports an efficient and rapid method of producing highly monodispersed InP quantum dots using a novel precursor-based colloidal synthesis in a noncoordinating solvent. The method also allows judicious control over the size of the quantum dots and can also be extended to produce other III−V quantum dots. In this paper, the synthesis and characterization of highly monodispersed InP quantum dots from newly prepared indium(III) carboxylate complexes in octadecene are detailed. When using indium(III) carboxylate as the indium precursor, no surfactant or coordinating solvents are required to prepare high-quality InP quantum dots in octadecene. The in situ formation of a surfactant upon injection of the phosphine precursor [P(SiMe3)3] helps control the growth of the resulting quantum dots. Structural and optical studies (continuous wave and time-resolved) have been performed on the as-prepared InP quantum dots. In addition, time-resolved photoluminescence has been conducted on etched InP quantum dots. The effects of the carboxylate chain length in indium(III) carboxylate and injection temperature on the growth and properties of quantum dots have been studied.

A novel approach for the sensitization of singlet oxygen has been developed which utilizes indirect excitation of the photosensitizer by two-photon-excited fluorescence resonance energy transfer (FRET) from separate chromophores assembled into a dendrimer. This approach effectively enhances the two-photon excitation efficiency of a known photosensitizer, without the sort of chromophore modifications that could lead to loss of photosensitization and other desirable photophysical properties. Photosensitization of singlet oxygen via excitation wavelengths transmissive to human body tissue (750−1000 nm) could alleviate the depth limitations of photodynamic therapy. The dendritic photosensitizer was prepared by grafting two-photon-absorbing chromophores and water-solubilizing moieties to a known multivalent porphyrin photosensitizer. Efficient FRET (>99% quenching of donor emission) between the peripheral donor two-photon-absorbing chromophores and the central acceptor photosensitizer at the core of the dendrimer was demonstrated under two-photon excitation conditions in an aqueous medium. Photosensitized production of singlet oxygen was monitored through chemical trapping and oxygen luminescence. Both methods independently demonstrated enhanced two-photon-induced singlet oxygen generation upon incorporation of two-photon-absorbing chromophores capable of efficient FRET to the photosensitizer.

Three novel two-photon absorbing (TPA) chromophores with 1,3,5-triazine as the π-electron deficient core, dialkylfluorene as aromatic bridges, and diphenylamino groups as the electron-donating end-groups were prepared. Designated as AF-450 (2,4,6-tris[7-(diphenylamino)-9,9-didecylfluoren-2-yl]-1,3,5-triazine), AF-455 (2,4,6-tris[9,9-bis(3,7-dimethyloctyl)-7-(diphenylamino)-fluoren-2yl]-1,3,5-triazine), and AF-457 (2,4,6-tris[(7-(diphenylamino)-9,9-diprop-2-enylfluoren-2-yl]-1,3,5-triazine), their overall molecular structure and local symmetry (D3h) are similar to those of previously reported three-armed AF-350 (N,N,N-tris[4-{7-(2-benzothiazolyl)-9,9-diethylfluoren-2-yl}phenyl]amine) and AF-380 (N,N,N,-tris[7-(2-benzothiazolyl)-9,9-diethylfluoren-2-yl]amine). Among the family of AFX chromophores previously reported by us, AF-450 possesses one of the largest effective TPA cross-sections (σ2‘ = 39 500 × 10^-50 cm⁴-sec/photon-molecule, or 39 500 GM) as determined by nonlinear transmission method in the nanosecond regime at 800 nm. In contrast, AF-455, a mixture of stereoisomers with the same chemical formula as AF-450, is a glassy material that becomes fluid (molasses-like) upon heating at 70−80 °C and has noticeably smaller effective σ2‘ value (33 300 GM). AF-457 (σ2‘ = 27 800 GM) with six allyl side groups was prepared as a precursor toward the synthesis of a TPA liquid. The intrinsic TPA cross-sections of these chromophores were also determined as a function of excitation wavelengths via a femtosecond white-light continuum generation and direct degenerate-TPA measurement technique. At the TPA peaks ~779 nm, their σ2‘ values are 216, 214, and 199 GM (±15%) for AF-450, AF-455, and AF-457, in that order. They are in the same trend as the nanosecond values, albeit two orders of magnitude lower.

The effects of the erbium concentration, crystal size, crystal phase, and different processing temperatures on the upconverted emission of Er³⁺ in BaTiO3 and TiO2 nanocrystals are reported. A cw diode laser at 975 nm was used as a pump source for resonant sequential excitation of the ⁴I11/2 and ⁴F7/2 levels. Green and red upconversion emission at 550 and 670 nm were observed from these oxide nanocrystals with 975 nm excitation. With the same Er³⁺ concentration, the upconversion emission intensity from BaTiO3 was higher than that observed in the TiO2 host. In the TiO2 matrix, the maximum upconversion emission intensity of Er³⁺ was found for samples calcined at 800 °C where both the anatase and the rutile phases were present. The observed emission characteristics and the pump intensity dependence of the luminescence intensity confirm that the upconverted emission in these materials is produced by two-photon excited-state absorption (ESA) processes.

We present electroluminescent (EL) properties of new blue−green organic dyes. The molecular structures of these dyes are based on 2,7-divinyl-9,9-bis(tert-butyl)fluorene, a π-electron bridge, end-capped with electron donor (D) and/or electron acceptor (A) group(s) to form D−π−A, D−π−D, and A−π−A structures. The donor group is a triphenylamine, and the acceptor group is a diphenyloxadiazole. We studied EL properties of these dyes in a single-layer EL device having the following structure:  ITO/PVK:DYE/Ca/Al. We found that both the wavelength of maximum emission and the threshold of EL depend on the structure and the concentration of the dye. Among the structure reported here, the D−π−A dye shows the highest EL performance, exhibiting a brightness of 498 cd/m² at an applied voltage of 25 V.

This paper presents the use of nanoscale chemistry to synthesize a multilevel, hierarchically built nanoparticle, which we define as a nanoclinic, for targeted diagnostics and therapy. This nanoclinic, produced by multistep chemistry in a nanosize micelle, consists of a thin silica shell encapsulating magnetic (Fe2O3) nanoparticles and fluorescent dyes for enhanced contrast magnetic resonance and optical imaging and magnetic-induced cancer therapy. Furthermore, the surface of these prototype nanoclinics is functionalized with a biotargeting group, luteinizing hormone-releasing hormone (LH−RH). In the work reported here, the LH−RH targets receptor-specific cancer cells for utilization in imaging and investigation of biological effects. The structure and function of these nanoclinics have been characterized using electron and X-ray diffractions, transmission electron microscopy, atomic force and scanning electron microscopy and two-photon laser scanning microscopy. Targeting of the receptor-specific cells has been demonstrated, along with the demonstration of a new mechanism of selective destruction of cancer cells, in a dc magnetic field, using these magnetic nanoclinics.

A new series of linear, asymmetrical diphenylaminofluorene-based chromophores (AFX) with various strong π-electron acceptors were synthesized and evaluated for two-photon absorptivity. These chromophores were studied to determine a suitable replacement for 2-(4-vinyl)pyridine, the π acceptor for our previously reported AFX series, which contains a photochemically and thermo-oxidatively unstable olefinic unit. In addition to the benzoyl group (AF-370), these π-electron acceptors include 2-benzothiazolyl (AF-240), 2-benzoxazolyl (AF-390), 2-(N-phenyl)benzimidazolyl (AF-386), and 2-(3,4-diphenyl)imidazolyl (AF-385) moieties (five-membered heterocycles) and the 2-quinoxalinyl (AF-260) group (six-membered heterocycle). From nanosecond nonlinear transmission measurements, these new chromophores have effective two-photon cross sections (σ2‘) at 800 nm, spanning from 3.87 × 10^-48 cm⁴ s/(photon molecule) for AF-385 to 97.46 × 10^-48 cm⁴ s/(photon molecule) for AF-240. Two of them, 2-benzothiazolyl-end-capped AF-240 and benzoyl-containing AF-370 [σ2‘ = 84.32 × 10^-48 cm⁴ s/(photon molecule)] stand out as having relatively good, albeit lower, values of two-photon cross sections, as compared to that of previously reported N,N-diphenyl-7-[2-(4-pyridinyl)ethenyl]-9,9-didecyl-fluorene-2-amine, AF-50 [σ2‘ = 115.6 × 10^-48 cm⁴ s/(photon molecule)]. However, we observed that AF-240 was more photochemically robust than AF-50 when their THF solutions were subjected to repetitive and prolonged exposure to nanosecond laser radiation. Finally, on the basis of our nanosecond TPA cross-section data (σ2‘/MW values), the general trend for π-electron accepting ability, i.e., ability to accept charge transferred from diphenylamine appears to be as follows:  2-(4-vinyl)pyridine > 2-benzothiazolyl > benzoyl > 2-(N-phenylbenzimidazolyl > 2-quinoxalinyl > 2-benzoxazolyl > 2-(4,5-diphenyl)imidazoyl.

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. This value is orders of magnitude higher than commercially available organic dyes measured at the same wavelength. Although the process is thought to involve a combination of two-photon absorption and excited state absorption phenomena, the information gathered from these new families of dyes has provided an important first step in producing improved materials for use in many different two-photon technology application.

We show that a nanoscale polymerization reaction within the confinement of a reverse micellar cavity yields products with controlled conjugation lengths and, thus, controlled band gaps for applications to electronics and photonics. In addition, control of the physical size (length) of the polymer provides the prospects of monodispersity, improved processability, and preparation of nanocomposites. This novel approach has been successfully applied to produce controlled chain length poly(p-phenylenevinylene) (PPV), a polymer that has drawn considerable attention in recent years for its electroluminescence, nonlinear optical, and lasing properties.

SiO2/TiO2/poly(vinylpyrrolidone) (PVP) composite materials processed by the sol−gel technique were studied for optical waveguide applications. Change of refractive index through the range 1.39−1.65 at 633 nm (optical wavelength) was achieved by varying the ratio between the SiO2 and TiO2 concentrations. To produce low optical propagation loss in the waveguide, it was necessary to avoid the precipitation of TiO2 particles caused by the fast hydrolysis reaction of titanium alkoxide. By using titanium ethylhexoxide as a titanium alkoxide together with acetic acid and 2-propanol as the solvent, the precipitation of TiO2 was avoided in the TiO2 concentration range of up to 30 wt %, resulting in low optical propagation losses in the slab waveguide configuration. In the higher TiO2 concentration range, an additional measure, peptization was necessary. With this method, we could produce optical waveguides possessing optical propagation losses of 0.62 dB/cm or lower at 633 nm. Low optical propagation loss in all the TiO2 concentrations, from 0% TiO2/50% SiO2/50% PVP to 50% TiO2/0% SiO2/50% PVP was achieved. The reactions of the sol−gel precursors were also studied using UV−visible and FT-IR spectroscopy.