Mixed self-assembled monolayers of azobenzene photoswitches with trifluoromethyl and cyano end groups.

Mixed self-assembled monolayers (SAMs) of alkanethiolates carrying azobenzene chromophores with either a trifluoromethyl or a cyano substituent have been studied. High-resolution x-ray photoelectron spectroscopy proves that the ratio of adsorbed molecules can be arbitrarily adjusted via the molar fractions in solution. As a function of these molar fractions core level shifts are observed which are attributed to local work-function changes. By simulating the electric dipole field distribution, the continuous core level shifts are ascribed to a homogeneous mixture of molecules with different end groups adsorbed on adjacent lattice sites. Near-edge x-ray absorption fine structure measurements reveal formation of well-ordered SAMs. Despite the difference in dipole moment of the end groups, the molecular tilt and twist angles are identical for both single-component SAMs and a 1:1 mixed SAM.

Structure and excitonic coupling in self-assembled monolayers of azobenzene-functionalized alkanethiols.

Optical properties and the geometric structure of self-assembled monolayers of azobenzene-functionalized alkanethiols have been investigated by UV/visible and near edge X-ray absorption fine structure spectroscopy in combination with density-functional theory. By attaching a trifluoro-methyl end group to the chromophore both the molecular tilt and twist angle of the azobenzene moiety are accessible. Based on this detailed structural analysis the energetic shifts observed in optical reflection spectroscopy can be qualitatively described within an extended dipole model. This substantiates sizable excitonic coupling among the azobenzene chromophores as an important mechanism that hinders trans to cis isomerization in densely packed self-assembled monolayers.

Photochemistry of anthracene-9,10-endoperoxide.

The wavelength dependence of the photochemistry of anthracene-9,10-endoperoxide (APO) in acetonitrile was quantitatively investigated at 5 degrees C, with excitation varied from 240 to 450 nm. Anthracene (AC) and a diepoxide (DE) were identified as the main primary photoproducts. After short exposure times DE was at all wavelengths the dominating photoproduct, while AC was only formed for lambda

High-power fifth-harmonic generation of femtosecond pulses in the vacuum ultraviolet using a Ti:sapphire laser.

We demonstrate the generation of fifth-harmonic pulses at 161 nm, with an energy of up to 600 nJ and 160 fs pulse duration from a Ti:sapphire laser at 1 kHz repetition rate by four-wave difference-frequency mixing in argon-filled waveguides. The efficiency is greatly improved by coupling to higher-order transverse modes, as well as by coating the inner surface of the waveguide. A numerical model of the process yields an understanding of the main effects influencing the harmonic generation.

Administration of novel dyes for intraocular surgery: an in vivo toxicity animal study.

PURPOSE: To investigate the effect of intravitreal injections of new vital dyes on the retina, the retinal pigment epithelium (RPE) and the choroid in an in vivo rat model. METHODS: Rats were injected intravitreally with four dyes: light-green SF yellowish (LGSF), copper(II)phthalocyanine-tetrasulfonic acid (E68), bromphenol blue (BPB), and Chicago blue (CB) dissolved in physiologic saline solution (PSS) at concentrations of 0.5% and 0.02%. PSS served as the control. Additional animals were treated with single injections of 0.5%, 0.02%, 0.002%, and 0.0002% ICG or 0.002% E68 into one eye. Adverse effects on anterior and posterior segments were evaluated by slit lamp biomicroscopy and ophthalmoscopy. Retinal toxicity was assessed by histology and retinal ganglion cell (RGC) quantification 7 days after dye administration. RESULTS: Eyes treated with 0.5% E68, 0.5% ICG, or 0.5% CB showed discrete staining of both cornea and lens not seen at lower concentrations or with other dyes. Histology revealed dose-dependent reactions after E68 administration. ICG 0.5% induced significant thinning of inner retinal layers compared with PSS. ICG 0.02% caused focal degenerative changes of the outer retina in three of seven eyes, whereas 0.002% and 0.0002% ICG did not. CB led to heterogeneous morphologic alterations. BPB- or LGSF-treated eyes showed normal retinal morphology. ICG at all tested concentrations induced significant RGC loss, as did E68 at 0.5% but not at lower concentrations. CONCLUSIONS: BPB or LGSF produced no significantly detectable toxic effects on the retina in vivo. The safety of these new dyes must be established in other models and/or in preclinical studies before the clinical use of any of these dyes.

Short-term in vivo evaluation of novel vital dyes for intraocular surgery.

PURPOSE: To evaluate the staining characteristics and safety of potential new dyes for intraocular surgery in porcine eyes. METHODS: Four dyes in different solutions (light green SF yellowish [LGSF]: 2%; copper(II) phthalocyanine-tetrasulfonic acid [E68]: 2% and 0.5%; bromophenol blue [BPB]: 2%, 1%, and 0.2%; and Chicago blue [CB]: 2% and 0.5%) were included in this investigation. All dyes were dissolved and diluted using balanced salt solution (BSS plus; Alcon Laboratories, Inc., Fort Worth, TX). After triamcinolone-assisted vitrectomy on 10 porcine eyes in vivo, the dyes were first injected into the air-filled vitreous cavity. After 1 minute, the dye was removed by irrigation with BSS, and the staining effect was graded by two examiners. After vitrectomy, the same dyes and concentrations were injected in the air-filled anterior chamber to stain the lens capsule of the same eye. After surgery, the eyes were enucleated and underwent fixation for light and electron microscopy. The animals were killed by injection of pentobarbital (50 mg/kg). For controls, each BSS plus alone and indocyanine green 0.5% were applied in one eye. RESULTS: On the retinal surface, bright staining of the retinal surface was seen after application of BPB 2% and 1%. The staining effect was less pronounced but still very good using E68 2%, and CB 2% and weak using BPB 0.2%, E68 0.5% and CB 0.5% as well as indocyanine green 0.5%. No staining of the retinal surface but of the vitreous was seen after application of LGSF 2%. The lens capsule stained very well with E68 2%, CB 2% and 0.5%, and BPB 2%, 1%, and 0.2% but not with LGSF. No histologic abnormalities were seen after the application in any eye after dye injection. No dye-related complications occurred during surgery. CONCLUSION: In this study, we identified three dyes with satisfying staining characteristics in both anterior and posterior segments. Because BPB stained the retinal surface and lens capsule at a low concentration (0.2%) with no signs of toxicity, this dye seems to be the most promising candidate for application in humans.

Light absorbing properties of indocyanine green (ICG) in solution and after adsorption to the retinal surface: an ex-vivo approach.

BACKGROUND: To evaluate potential differences in light absorbing properties and stability of indocyanine green (ICG) adsorbed to the retinal surface and of ICG dissolved in water and balanced salt solution. METHODS: The retina of four human donor eyes was prepared by removing the vitreous from the retinal surface. The inner surface of the specimen was covered with two to three drops of a 0.05% or 0.15% ICG solution respectively. After 1 min, the dye was removed by careful irrigation using BSS plus. The retinal specimens were then investigated by diffuse reflection spectroscopy (UV/VIS/NIR Spectrometer Lambda 900/Perkin Elmer equipped with a PELA-1020 integrating sphere accessory) and their absorption evaluated by the Kubelka-Munk function. To control the sensitivity of the setting, diffuse reflectance spectra of ICG adsorbed to a cellulose membrane and Al(2)O(3) were measured. For comparison, absorption spectra of ICG dissolved in water and BSS plus solution were measured in relation to ICG concentration and time using an UV/VIS/NIR Spectrometer Lambda 900/Perkin Elmer. RESULTS: On the retinal surface, absorption spectra exhibited a steep increase of absorption beginning at 620 nm, with a maximum at 736 nm (0.05%) and a shoulder at 745 (0.15%) and a second maximum at approximately 800 nm for both concentrations. Repeated measurement of the retinal surface 13 days after the ICG exposure revealed no changes in the position of the maxima as compared to the initial measurements. Light absorbing properties of ICG on cellulose or Al(2)O(3) are similar to those seen on the retinal surface with respect to the pattern and location of absorption maxima. In contrast, ICG dissolved in water or BSS plus disclosed variations in absorption characteristics depending on dye concentration, solute and time of measurement. CONCLUSIONS: Absorption characteristics and stability of ICG bound to the retinal surface could be of relevance when investigating potential pathomechanisms of ICG related toxicity, which might be related not only to intraoperative but also to postoperative light exposure of patients after intravitreal use of ICG.

An evaluation of novel vital dyes for intraocular surgery.

PURPOSE: To evaluate systematically the staining characteristics and safety of potential new dyes for intraocular surgery. METHODS: Six dyes were included in the investigation: light green SF (LGSF) yellowish, E68, bromophenol blue (BPB), Chicago blue (CB), rhodamine 6G, rhodulinblau-basic 3 (RDB-B3). All dyes were dissolved and diluted in a balanced saline saline solution. The light-absorbing properties of each dye were measured at a concentration of 0.05% between 200 and 1000 nm. Staining characteristics were examined by staining lens capsule tissue and epiretinal membranes (ERMs), removed intraoperatively, with dye concentrations of 1.0%, 0.5%, 0.2%, and 0.05%. Enucleated porcine eyes (postmortem time, 9 hours) were also stained. Dye-related toxicity was evaluated by a colorimetric test (MTT) measuring the inhibition of retinal pigment epithelium (RPE) cell proliferation (ARPE-19 and primary human RPE cells, passages 3-6). Cell viability was also quantified based on a two-color fluorescence cell-viability assay. Dyes were investigated in concentrations of 0.2% and 0.02%. RESULTS: All dyes investigated in this study stained human lens capsules, removed intraoperatively; ERMs, peeled during macular pucker surgery; and enucleated porcine eyes, depending on the concentration applied. The long-wavelength absorption maximum of the dyes was within the range of 527 to 655 nm at concentrations of 0.05%. Rhodamine G6 and RDB-B3 showed adverse effects on ARPE-19 cell proliferation at a concentration of 0.2% and were excluded from further investigation in primary RPE cells. The remaining four dyes showed no toxic effect on ARPE-19 and primary RPE cell proliferation at concentrations of 0.2% and 0.02%. Cell viability was affected by LGSF yellowish (0.2%) and CB (0.2% and 0.02%). Two dyes (E68 and BPB) showed no relevant toxicity in vitro. CONCLUSIONS: The systematic evaluation of dyes for intraocular use seems mandatory. In this study four dyes were identified with effective staining characteristics, with two of these dyes having no detectable toxic effect on RPE cells in vitro.