Fully independent photochemical reactivity in one molecule.

We introduce a chemically λ-orthogonal bichromophore triggered simply by different colours of light, enabling two different photochemical reactions in one molecule. Uniquely, the short wavelength (λ = 314 nm) does not trigger the red-shifted reaction system (λ = 416 nm), opening possibilities for the light controlled gating of specific molecular sites independent of wavelength.

Exploiting λ-Orthogonal Photoligation for Layered Surface Patterning.

We exploit λ-orthogonal photoligation of nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) chemistry to generate complex, interconnected surface modifications via a simple layered surface patterning approach. By judicious choice of activating chromophores, we introduce a one pot reaction where nitrile imine formation can be triggered independently of other tetrazoles present. When irradiated with visible light, a tetrazole bearing a pyrene chromophore undergoes quantitative elimination of nitrogen to release nitrile imine (which subsequently undergoes trapping with a dipolarophile in a 1,3 dipolar cycloaddition) whereas a tetrazole bearing a phenyl moiety remains unreacted. Subsequent irradiation of the solution with UV light yields the N-phenyl containing nitrile imine quantitatively, while the pyrene pyrazoline adduct remains unchanged. This λ-orthogonal photoligation was subsequently exploited for the generation of layered patterned surfaces. Specifically, the visible light active tetrazole was grafted to a silicon wafer and subsequently photolithographically patterned with a dipolarophile modified with a UV-active tetrazole. Various electron deficient olefins were then patterned in a spatially resolved manner relying on different light activation. The desired functionality was successfully imaged on the silicon wafers using time-of-flight-secondary ion mass spectrometry (ToF-SIMS), demonstrating that a powerful mask-less lithographic platform technology has been established.

Photo-Induced Click Chemistry for DNA Surface Structuring by Direct Laser Writing.

Oligonucleotides containing photo-caged dienes were prepared and shown to react quantitatively in a light-induced Diels-Alder cycloaddition with functional maleimides in aqueous solution within minutes. Due to its high yield and fast rate, the reaction was exploited for DNA surface patterning with sub-micrometer resolution employing direct laser writing (DLW). Functional DNA arrays were written by direct laser writing (DLW) in variable patterns, which were further encoded with fluorophores and proteins through DNA directed immobilization. This mild and efficient light-driven platform technology holds promise for the fabrication of complex bioarrays with sub-micron resolution.

Spatially resolved photochemical coding of reversibly anchored cysteine-rich domains.

We present a novel methodology to generate recodable surfaces using cysteine-rich domains (CRD) via a combination of photolithography and reversible covalently peptide-driven disulfide formation. Therefore, two 21mer CRD peptide derivatives were synthesized, one bearing an electron deficient fumarate group for immobilization via nitrile imine-ene mediated cycloaddition (NITEC) to a tetrazole-functional surface. Secondly, a bromine moiety is introduced to the CRD for analytic labelling purposes to detect surface encoding. The photolithography is conducted by selectively passivating the surface with a polyethylene glycol (PEG)-fumarate via NITEC using a photomask in a dotted pattern. Consecutively, the CRD-fumarate is immobilized via NITEC adjacent to the PEG-functional areas to the unaffected tetrazole covered surface layer. Subsequently, the CRD-bromide is covalently linked to the CRD-fumarate by forming disulfide bonds under mild reoxidative conditions in a buffer solution. The CRD-bromide is released from the surface upon reduction to recover the prior state of the surface without the bromine marker. The analysis of the CRD precursors is based on electrospray ionization mass spectrometry (ESI-MS). The surface analytics were carried out via time-of-flight secondary ion mass spectrometry (ToF-SIMS), unambiguously verifying the successful immobilization as well as coding and decoding of the CRD-bromide on the surface based on dynamically reversible disulfide bond formation.

Photo-induced chemistry for the design of oligonucleotide conjugates and surfaces.

A photocaged diene is introduced at the 5'-end of oligonucleotides using the H-phosphonate approach. The photoenol-functionalized DNA is subsequently employed for the conjugation to a protein and the spatially controlled immobilization onto surfaces using a light-induced Diels-Alder cycloaddition. Fully functional protein-DNA conjugates and patterned DNA surfaces are obtained under mild irradiation conditions.

Fast and Simple Preparation of Patterned Surfaces with Hydrophilic Polymer Brushes by Micromolding in Capillaries.

Micropatterns of hydrophilic polymer brushes were prepared by micromolding in capillaries (MIMIC). The polymers are covalently bound to the surfaces by a rapid hetero Diels-Alder reaction, constituting the first example of polymers grafted to surfaces in a defined pattern by MIMIC. The polymers [poly(acrylic acid), poly(hydroxyethyl acrylate), and poly(tetraethylene glycol acrylate) ranging in molecular weight from 1500 to 6000 g mol(-1)] were prepared with narrow dispersities via the reversible addition-fragmentation chain transfer (RAFT) process using a highly electron deficient RAFT agent that can react with surface-anchored dienes such as cyclopentadiene. We demonstrate that the anchoring method is facile to perform and highly suitable for preparing patterned surfaces that are passivated against biological impact in well-defined areas.

Designing Molecular Printboards: A Photolithographic Platform for Recodable Surfaces.

A light induced strategy for the design of ß-cyclodextrin (CD) based supramolecular devices is introduced, presenting a novel tool to fabricate multifunctional biointerfaces. Precision photolithography of a modified ß-CD was established on a light sensitive tetrazole surface immobilized on a bioinspired polydopamine (PDA) anchor layer via various shadow masks, as well as via direct laser writing (DLW), in order to craft any desired printboard design. Interfacial molecular recognition provided by light generated cavitate domains was demonstrated via spatially resolved encoding, erasing, and recoding of distinct supramolecular guest patterns. Thus, the light directed shaping of receptor monolayers introduces a powerful path to control supramolecular assemblies on various surfaces.

Photo-induced surface encoding of gold nanoparticles.

Photoreactive gold nanoparticles (NP) can be encoded in a spatially resolved fashion using direct laser writing techniques into variable patterns. The surface of the gold nanoparticles is imparted with photoreactivity by tethering photo-caged dienes ('photoenols'), which are able to undergo a rapid Diels-Alder cycloaddition with surface anchored enes. Subsequent to surface encoding, the particles feature residual caged dienes, which can be reactivated for secondary surface encoding.