Super-resolution Reflection Microscopy via Absorbance Modulation.

In recent years, fluorescence microscopy has been revolutionized. Reversible switching of fluorophores has enabled circumventing the limits imposed by diffraction. Thus, resolution down to the molecular scale became possible. However, to the best of our knowledge, the application of the principles underlying super-resolution fluorescence microscopy to reflection microscopy has not been experimentally demonstrated. Here, we present the first evidence that this is indeed possible. A layer of photochromic molecules referred to as the absorbance modulation layer (AML) is applied to a sample under investigation. The AML-coated sample is then sequentially illuminated with a one-dimensional (1D) focal intensity distribution (similar to the transverse laser mode TEM01) at wavelength λ1 = 325 nm to create a subwavelength aperture within the AML, followed by illumination with a Gaussian focal spot at λ2 = 633 nm for high-resolution imaging. Using this method, called absorbance modulation imaging (AMI) in reflection, we demonstrate a 2.4-fold resolution enhancement over the diffraction limit for a numerical aperture (NA) of 0.65 and wavelength (λ) of 633 nm.

Bis(thienyl)ethenes with α-methoxymethyl groups. Syntheses, spectroscopic Hammett plots, and stabilities in PMMA films.

A series of bis(thienyl)ethenes (BTEs) possessing perfluorocyclopentene backbones and methoxymethyl groups (MOM) in the 2/2'-positions of the thiophenes was prepared and examined. The substitution pattern of the 5/5'-positions was varied, covering the range from electron-donating to electron-withdrawing. The substituent effects of the absorption wavelengths of the ring-opened and the ring-closed isomers, which are interconverted by reversible 6π-electrocyclizations and cycloreversions, are studied by means of the spectroscopic Hammett equation and the Hammett-Brown equation. Excellent correlations of these linear free energy relationships were found, when the σp values of the Hammett equation, which summarize inductive, mesomeric and field effects, were replaced to the Hammett-Brown σp+ and σp- values which also take direct conjugation into account. We studied solvent effects on the spectroscopic properties and embedded the BTEs into polymethylmethacrylate (PMMA) coatings to examine their fatigue resistance. By our studies, the spectroscopic properties of BTEs can be adjusted by variation of the substitution pattern to a desired excitation wavelength for switching processes.

Surface Tuning of Wood via Covalent Modification of Its Lignocellulosic Biopolymers with Substituted Benzoates-A Study on Reactivity, Efficiency, and Durability.

Chemical modification of wood applying benzotriazolyl-activated carboxylic acids has proven to be a versatile method for the durable functionalization of its lignocellulosic biopolymers. Through this process, the material properties of wood can be influenced and specifically optimized. To check the scope and limitations of this modification method, various benzamide derivatives with electron-withdrawing (EWG) or electron-donating (EDG) functional groups in different positions of the aromatic ring were synthesized and applied for covalent modification of Scots pine (Pinus sylvestris L.) sapwood in this study. The bonded amounts of substances (up to 2.20 mmol) were compared with the reactivity constants of the Hammett equation, revealing a significant correlation between the modification efficiency and the theoretical reactivity constants of the corresponding aromatic substitution pattern. The successful covalent attachment of the respective substituted benzamides was proven by attenuated total reflection infrared (ATR-IR) spectroscopy, while the stability of the newly formed ester bond was proven in a standardized leaching test.