Photoinduced Reversible Formation of Microfibrils on a Photochromic Diarylethene Microcrystalline Surface

Abstract

Lotus and taro leaves have hydrophobic surfaces, which in nature consist of micrometer-scale rods or projections that exhibit a super water-repellent property called the lotus effect. The contact angle of a water droplet on such surfaces is 161.0 AE 2.78. Recently, many reports concerning changes in water droplet contact angle as a result of changes in surface morphology and surface polarity have been published. [1] Additionally, changes in photoresponsive wettability have also been reported.[2]Herein, we report a new photoinduced change in surface morphology that provides superhydrophobic properties, obtained by the photoinduced reversible formation of fine fibril structures on coated microcrystalline surfaces. The origin of the reversible formation of fibrils is the photoisomerization of a photochromic diarylethene molecule 1 (see Scheme 1) of a thin film. The reversible changes in surface morphology of a thin film made from photochromic diarylethene 1 were followed by scanning electron microscopy (SEM), optical microscopy, and contact angle measurements of a water droplet. The film was prepared by coating a solution of 1 in chloroform onto a substrate, which gave a contact angle of the water droplet of around 1208. Upon irradiation with UV light, the film surface became superhydrophobic (contact angle 1638). SEM images showed that the surface was covered with microfibrils of diameter around 1 mm. Upon irradiation with visible light, the surface again became flat and recovered the initial contact angle of 1208.Diarylethene derivatives are promising artificial photoresponsive molecules that show reversible transformation between open-and closed-ring isomers with different absorption spectra.[3] As they also show thermally irreversible and fatigue-resistant photochromic performance, [4] intensive studies have aimed at applications such as molecular memories and switches.[5-13] Herein, we report a new function for the cast film of a derivative.There are two approaches to controlling surface wettability. One is to change the surface morphology, because it is known that increasing surface roughness results in a superhydrophobic surface, an effect that is widely observed on lotus leaves. [14,15] Such micrometer-scale rugged or fractal structures were also artificially prepared to make superhydrophobic surfaces. [1b, 16, 17] The other approach is a change of polarity. [18][19][20][21][22] Several reports have attempted to control surface wettability by using photochromic compounds that change the surface polarity.[21] We report changes in photoinduced wettability based on the changes in morphology of a photochromic diarylethene crystal and thin film.The photochromism of a diarylethene, 1,2-bis(2-methoxy-5-trimethylsilylthien-3-yl)perfluorocyclopentene(1 o; Scheme 1), in a hexane solution is shown in the SupportingInformation. The open-ring isomer is colorless, and absorption maxima of the spectrum were observed at l = 255 (e = 2.8 10 4 m À1 cm À1 ) and 325 nm (e = 7.7 10 3 m À1 cm À1 ). Upon UV irradiation (254 n...

Organic Photofunctional Materials Composed of Azobenzene Derivatives: Liquid-solid Phase Transition in Multi Azobenzene Compounds with Partially Substituted Structures

“…[7,8,9,] Amongst them, we have recently reported light responsive, reworkable adhesives in multi azobenzene compounds with reversible liquid-solid phase change properties. [10] Related phase transitions have been reported for fluidization of azobenzene polymers using irradiation with light [11], changing the melting point in crystals of diarylethanes using photoisomerization [12,13] and "photomelting" of crystals of cyclic azobenzene dimers at room temperature [14,15]. Multi-azobenzene compounds that we demonstrated the first, reversible adhesion force change upon light stimulation are tetra-, hexa-, or octa-substituted sugar alcohols bearing mesogenic azobenzene chains.…”

Control of Surface Wettability and Photomicropatterning with a Polymorphic Diarylethene Crystal upon Photoirradiation

“…[18][19][20] The change in the surface topology by the crystal growth of a photochromic diarylethene has recently been reported. [21,22] In this case, the contact angle with water changed from 1208 to 1638 upon UV light irradiation because of the generation of the closed-ring isomer crystal of the fibrils on the crystal surface. The reversible changes in the contact angle were attributed to reversible changes in the surface roughness.…”

Theoretical Explanation of the Lotus Effect: Superhydrophobic Property Changes by Removal of Nanostructures from the Surface of a Lotus Leaf

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Recently, we have reported photoinduced reversible wettability changes concomitant with topographical changes on the microcrystalline surface of diarylethene 1. [14][15][16] By applying photocontrol of the type and size of the crystals, we could control the photoswitching between two types of water-adhesive superhydrophobic surfaces showing lotus and rose-petal effects. The observed dynamic wetting behavior was explained by a simple scenario that considers the trade-off between the surface-structure-dependent adhesion energy and the potential energy change.…”