Rapid and directional movement of water droplets across a photopolymer surface with inscribed wettability and Laplace pressure gradient is demonstrated.

No abstract

In this study, the bifunctional hydroxyketone based photoinitiator (PI) 1,1′‐{[(2,3‐dihydroxybutane‐1,4‐diyl)bis(oxy)]bis(4,1‐phenylene)}bis(2‐hydroxy‐2‐methylpropan‐1‐one) (Di‐PI) is synthesized with the aim to facilitate a highly photoactive water‐soluble PI which offers high migration stability. Di‐PI provides a five times higher water‐solubility than the state of the art water soluble PI 2‐hydroxy‐1‐[3‐(hydroxymethyl)phenyl]‐2‐methyl‐1‐propanone (I2959). Photo differential scanning calorimetry (Photo‐DSC) measurements reveal that the curing speed and conversion of N‐acroylmorpholine (NAM) in aqueous solution containing 0.5 mol% of Di‐PI are only slightly lower than formulations containing the reference PI I2959 in a concentration of 1 mol%. Most importantly, Di‐PI offers almost identical activity in dipropylene glycol diacrylate (DPDA) as I2959, although its migration from cured DPDA is significantly reduced by a factor of 7.6 compared to I2959.

The breaking of molecular symmetry through photoexcitation is a ubiquitous but rather elusive process, which, for example, controls the microscopic efficiency of light harvesting in molecular aggregates. A molecular excitation within a π-conjugated segment will self-localize due to strong coupling to molecular vibrations, locally changing bond alternation in a process which is fundamentally nondeterministic. Probing such symmetry breaking usually relies on polarization-resolved fluorescence, which is most powerful on the level of single molecules. Here, we explore symmetry breaking by designing a large, asymmetric acceptor-donor-acceptor (A-D-A) complex 10 nm in length, where excitation energy can flow from the donor, a π-conjugated oligomer, to either one of the two boron-dipyrromethene (bodipy) dye acceptors of different color. Fluorescence correlation spectroscopy (FCS) reveals a nondeterministic switching between the energy-transfer pathways from the oligomer to the two acceptor groups on the submillisecond timescale. We conclude that excitation energy transfer, and light harvesting in general, are fundamentally nondeterministic processes, which can be strongly perturbed by external stimuli. A simple demonstration of the relation between exciton localization within the extended π-system and energy transfer to the endcap is given by considering the selectivity of endcap emission through the polarization of the excitation light in triads with bent oligomer backbones. Bending leads to increased localization so that the molecule acquires bichromophoric characteristics in terms of its fluorescence photon statistics.

Tetrabromo aromatics can be synthesized by the Fischer-Zimmermann condensation of appropriate pyrylium salts with arylene dicarboxylic acid salts. Their cyclization by intramolecular Yamamoto coupling yields strained bicyclophanes with adjustable sizes and different intraannular bridges. All compounds adsorb at the solid/liquid interface on highly oriented pyrolytic graphite (HOPG) and are investigated by scanning tunneling microscopy (STM) with submolecular resolution. The observed two-dimensional (2D) supramolecular nanopatterns depend only on the sizes and alkoxy periphery of the cyclophanes and are independent of the specific structures of the intraannular bridges. Since the central arylene moieties of the smaller species are oriented perpendicular to the planes of the bicyclophanes, their substituents protrude from the surface by up to 1.6 nm after adsorption. Therefore, these molecules are attractive platforms for addressing the volume phase above the graphite surface.