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Inspired by the superhydrophobic effect displayed in nature, we set out to mimic the interplay between the chemistry and physics in the lotus leaf to see if the same design principle can be applied to control wetting and adhesion between toners and inks on various printing surfaces. Since toners and inks are organic materials, superoleophobicity has become our design target. In this work, we report the design and fabrication of a model superoleophobic surface on silicon wafer. The model surface was created by photolithography, consisting of texture made of arrays of ∼3 μm diameter pillars, ∼7 μm in height with a center-to-center spacing of 6 μm. The surface was then made oleophobic with a fluorosilane coating, FOTS, synthesized by the molecular vapor deposition technique with tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane. Contact angle measurement shows that the surface exhibits super repellency toward water and oil (hexadecane) with a water and hexadecane contact angles at 156° and 158°, respectively. Since the sliding angles for both liquids are also very small (∼10°), we conclude that the model surface is both superhydrophobic and superoleophobic. By comparing with the contact angle data of the bare silicon surfaces (both smooth and textured), we also conclude that the superoleophobicity is a result of both surface texturing and fluorination. Results from investigations of the effects of surface modification and pillar geometry indicate that both surface oleophobicity and pillar geometry are contributors to the superoleophobicity. More specifically, we found that superoleophobicity can only be attained on our model textured surface when the flat surface coating has a relatively high oleophobicity (i.e., with a hexadecane contact angle of >73°). SEM examination of the pillars with higher magnification reveals that the side wall in each pillar is not smooth; rather it consists of a ∼300 nm wavy structure (due to the Bosch etching process) from top to bottom. Comparable textured surfaces with (a) smooth straight side wall pillars and (b) straight side wall pillars with a 500 nm re-entrant structure made of SiO(2) were fabricated and the surfaces were made oleophobic with FOTS analogously. Contact angle data indicate that only the textured surfaces with the re-entrant pillar structure are both superoleophobic and superhydrophobic. The result suggests that the wavy structure at the top of each pillar is the main geometrical contributor to the superoleophobic property observed in the model surface.

The absorption and the steady-state fluorescence emission of a class of donor-acceptor-donor (D-A-D) molecules, bis-[4-(dimethylamino)phenyl]squaraine and its derivatives (1-19), have been studied. Squaraines generally exhibit intense solution absorption in the red (e ~3 X 105 cm"1 M"1). All substituents studied in this work exert a bathochromic effect on the absorption. The effect is small and is attributable to the minor involvement of the donor group in the S0 -*• S, excitation. In conjunction with emission data, we are able to show that the bathochromic shift originates from the solute-solvent complex and that the complexation constant increases as the D-A-D charge-transfer character of squaraine increases. Electronic and steric factors affecting the D-A-D character and subsequently the absorption maximum are discussed in terms of the solute-solvent complex model. Multiple-emission bands are observed in the fluorescence spectra of 1-19. Three bands, a, ß, and y, are identified from their typical Stokes shifts. Controlled experiments showed that the multiple-emission bands are intrinsic emissive properties of squaraines. Results from mixed-solvent experiments, solvent-effect studies, and temperature-effect studies show that squaraines form solute-solvent complexes in organic solvents. A photophysical model to account for the multiple emission is proposed. Excitation of squaraine in solution results in two excited states, namely, the excited state of free squaraine and the excited state of the solute-solvent complex. These two excited states emit photons to give the «-emission and the /3-emission. Rotational relaxation(s) (around the C-C bond between the phenyl ring and the four-membered ring of squaraine) is (are) shown to be the major radiationless decay process(es) of these two excited states. As a result, a twisted relaxed excited state is generated. This relaxed excited state can undergo a rotational relaxation to the ground state or emit a photon to give the -emission. The effect of structural changes on the multiple emission is discussed.

The synthesis of several amphiphilic squaraine dyes and a study of their aggregation behavior and photophysics are reported. The several different squaraines are found to give spectrally blue-shifted aggregates in aqueous and mixed aqueous-organic solution and in microheterogeneous media (bilayer vesicles). While in some cases an intermediate dimer can be detected in the monomer to aggregate conversion process, in others direct conversion of monomer to aggregate is observed. The aggregation number can be determined together with the equilibrium constant and thermodynamic parameters for some of the squaraines in different environments. In several cases the aggregation number is found to be ca. 4. The finding of a strong induced circular dichroism signal when the aggregate (but not dimer or monomer) is generated in the presence of a chiral host (or counterion) suggests that the aggregate is chiral. From these results and molecular simulations indicating that an extended monolayer of some of the squaraines adopts a glide or herringbone lattice we propose a chiral "pinwheel" structure for the unit aggregate and suggest that extended aggregate structures or crystals may be a mosaic of these unit aggregates. In contrast to the monomers, which are strongly fluorescent, the squaraine dimers and aggregates are nonfluorescent and have extremely short exciton lifetimes, as indicated by transient spectroscopy.