9 research outputs found
Guanine Crystallization in Aqueous Solutions Enables Control over Crystal Size and Polymorphism
Anhydrous
guanine crystals are among the most widespread organic
crystals used by organisms to produce structural colors. The main
advantage of guanine is its exceptionally high refractive index in
the reflecting direction (∼1.8). For the same reason, guanine
is a promising candidate material for a variety of different optical
applications. Crystallization of guanine is challenging and usually
involves using polar aprotic organic solvents such as dimethyl sulfoxide
(DMSO). Here, we show that the crystallization of guanine from aqueous
solutions is possible under conditions that provide control over crystal
polymorphism and size. Using this approach we were able produce large
crystals of the elusive guanine monohydrate phase. We were also able
to rationalize the formation of the different phases obtained as a
function of which tautomer of guanine is stable in solutions of varying
pH
Electrochromic Metallo-Organic Nanoscale Films: Fabrication, Color Range, and Devices
In this study, we demonstrate a versatile
approach for the formation
of electrochromic nanoscale assemblies on transparent conductive oxides
on both rigid and flexible substrates. Our method is based on the
application of alternating spin-coated layers of well-defined metal
polypyridyl complexes and a palladium(II) salt to form electrochemically
addressable films with a high chromophore density. By varying the
central metal ion of the polypyridyl complexes (Os, Ru, and Fe) and
their ligands and by mixing these complexes, coatings with a wide
range of colors can be achieved. These coatings cover a large area
of RGB color space. The coloration intensities of these nanoscale
films can be tuned by the number of deposition steps. The materials
have very attractive ON/OFF ratios, electrochemical stabilities, and
coloration efficiencies. Reversible color-to-colorless and color-to-color
transitions were demonstrated, and the films were further integrated
into sandwich cells