Reversible Photoswitchable Wettability in Noncovalently Assembled Multilayered Films

Abstract

Reversible and irreversible photoinduced changes in surface wettability were observed in noncovalently assembled multilayered films. The multilayered films studied were fabricated from a self-assembled monolayer (SAM) consisting of 4-(10-mercaptodecyloxy)pyridine-2,6-dicarboxylic acid on gold, Cu(II) ions complexed to the pyridine head group of the SAM, and either cis- (film 1) or trans- (film 2) stilbene-4,4'-dicarboxylic acid complexed to the Cu(II) ions. Irradiation of film 1 at wavelengths corresponding to the absorption band of the cis-stilbene isomer resulted in an irreversible chemical change and an irreversible increase in wettability, as indicated by surface contact angle and grazing incidence IR measurements. However, no evidence for cis-/trans-photoisomerization was observed. Films 3 and 4, similar to films 1 and 2 in that they consist of an underlying SAM, an intermediate layer consisting of Cu(II) ions, and either cis- or trans-stilbene-4,4'-dicarboxylic acid as the capping ligand, were fabricated with a mixed SAM that contained both 4-(10-mercaptodecyloxy)pyridine-2,6-dicarboxylic acid and 4-tert-butylbenzenethiol. Irradiation of these films at wavelengths corresponding to stilbene isomer absorption bands resulted in reversible cis- to trans- (film 3) and trans- to cis- (film 4) photoisomerization and reversible switching of the surface wettability between a low wetting state (cis-stilbene) and a high wetting state (trans-stilbene). The difference in observed behavior between films 1 and 2 and films 3 and 4 is attributed to the greater surface spacing afforded by the mixed monolayer, which allows greater conformational flexibility and lowers the steric barriers to isomerization.

Reversibly switchable wettability

“…In addition to semiconductor inorganic oxides, some organic materials containing photochromic functional groups, such as azobenzenes, 62 spiropyrans, 63 dipyridylethylenes, 64 stilbenes, 65 and pyrimidines 66 also have the ability to undergo reversible transition of conformation triggered by UV/visible irradiation, leading to changes in their wetting properties. 67 Among these materials, azobenzene and its derivatives are particularly promising as photo-stimulated materials, and they have been widely investigated as such.…”

The impact of trans/cis photoisomerization on photoinduced electron transport between 4,4′-stilbenedicarboxylic acid and columnar perylenediimide aggregates in water

“…1, trans-SDBA presents absorption bands at 342, 326, and 313 nm. Under irradiation, the band intensities of these featured absorptions of trans-SDBA decrease, while the intensities of the featured bands of cis-SDBA at 302 and 235 nm [34] increase gradually. After irradiation for 30 s, the spectrum reaches a stable state and keeps unchanged under irradiation for even longer time ( †Figure S1), indicating an equilibrium achieved for the photoisomerization.…”

“…Trans-SDBA was purchased from Alfa Aesar (96 %). Cis-SDBA was obtained from configuration transformation of trans-SDBA under the irradiation of Xe lamp (500 W, LSH-X500) with 310 nm optical filter [34].…”

Switchable and Reversible Superhydrophobic Surfaces: Part One

“…Organic chemicals containing photochromic functional groups such as azobenzenes [115], diarylethenes, spiropyrans [116], bipyridyl ethylenes [117], stilbenes [118] or pyrimidines [119] can follow a reversible transition by UV/vis light, which can lead to differences of wettability. Among them, azobenzene group and its derivatives are extremely promising as photosensitive materials and were highly studied in the literature [120][121][122][123][124][125][126][127][128][129][130][131][132][133][134][135].…”