A Mild Photoactivated Hydrophilic/Hydrophobic Switch

Abstract

Surface modification using light is one of the most powerful methods for controlling the physical and chemical properties offunctionalized surfaces. In this paper, we report on systems where soft UV irradiation (lambda = 365 nm) converts a "low" activity fluorocarbon to a "high" activity amine-functionalized surface. An amine-functionalized SAM (self-assembled monolayer) is first masked using a tertiary amine catalyzed reaction with an N-hydroxysuccinimidyl carbonyl reagent. This mild, room-temperature reaction introduces a hydrophobic photocleavable nitrobenzyl "protecting group" terminated with a fluorocarbon end-chain. UV irradiation (lambda = 365 nm) of this hydrophobic/fluorocarbon surface cleaves the nitrobenzyl residue, returning the surface to the original hydrophilic/amine-functionalized state. This provides a mild, generic method of producing surfaces with hydrophilic/hydrophobic patterns or patterned with amine functional residues. Two different protecting groups, one terminated with a single and the other with three fluorocarbon end chains, are compared. In the case of the more bulky protecting group, only a small proportion of the amine residues react, but the surface is equally hydrophobic and the amine residues equally well shielded from further reaction. Surfaces are characterized by X-ray photoelectron spectroscopy, ellipsometry, surface potential, and contact angle measurements. Images of the photopatterned SAMs were obtained using scanning electron microscopy.

Soft Ultraviolet (UV) Photopatterning and Metallization of Self-Assembled Monolayers (SAMs) Formed from the Lipoic Acid Ester of α-Hydroxy-1-acetylpyrene: The Generality of Acid-Catalyzed Removal of Thiol-on-Gold SAMs using Soft UV Light

“…3,4 Although most workers have concentrated on the photochemistry of ortho nitrobenzyl derivatives, almost any preparative photochemical reaction can be adapted for use in the SAM environment. 5,6 However, preparative photochemical reactions that give high yields in dilute solution do not necessarily…”

Photo-deprotection patterning of self-assembled monolayers

“…SAMs that are designed to photo-deprotect under soft UV light can be combined with simple alkanethiol SAMs (e.g., Octodecanethiol [44]) to produce new geometries not easily achieved using deep UV light or microcontact printing alone. Ryan et al [45] demonstrated that SAMs of methoxy-nitrobenzyl derivatives could be photopatterned to produce 'three-component' surface functionality.…”

“…Several researchers have demonstrated that photopatterning can be achieved using soft UV ( ¼ 365 nm, h $ 3.4 eV) light by incorporating photo-reactive orthonitrobenzyl chromophores [42][43][44][45][46][47][48][49][50][51][52][53][54][55]. At this wavelength, the photon energy is not sufficient to cause any significant photo-oxidisation of the SAM headgroups, and so we rely upon photochemistry to cleave the molecules at a designated bond to reveal new functionality.…”

“…The first system was an amine functionalised SAM that was 'protected' by a nitrobenzyl derivative with a semi-fluorinated tail group to produce CF 3 functionality. These SAMs were photo-deprotected to reveal amine functionality [44]. The second system reported was based on disulphide derivatives that contained nitrobenzyl groups.…”

Reversible metallisation of soft UV patterned substrates

“…31 The use of soft UV (365 nm) photolithography of ortho-nitrobenzyl protected SAMs provides a potentially attractive alternative since this offers much greater control over the chemical functionality of the surface. [32][33][34] Recently, we have shown that it is possible to obtain photolysis yields of ~ 95%…”