Combining Photodeprotection and Ligation into a Dual‐Color Gated Reaction System

Abstract

We report a photochemical reaction system which requires activation by two colors of light. Specifically, a dual wavelength gated system is established by fusing the visible light mediated deprotection of a dithioacetal with the UV light activated Diels–Alder reaction of an o‐methylbenzaldehyde with N‐ethylmaleimide. Critically, both light sources are required to achieve the Diels–Alder adduct, irradiation with visible or UV light alone does not lead to the target product. The introduced dual gated photochemical system is particularly interesting for application in light driven 3D printing, where two color wavelength activated photoresists may become reality.

Colorful 3D Printing: A Critical Feasibility Analysis of Multi-Wavelength Additive Manufacturing

“…PI-based chain-growth via an interdependent system of single-wavelength responsive molecules for AND+OR-type network formation: (d) similar open/closed ring isomers that were utilized in (c) as solution masks for radical PIs and (e) a radical PI for the radical photopolymerization of acrylates in combination with a photoacid generator (PAG) for the cationic photopolymerization of epoxides b Uncatalyzed light-initiated step-growth through chromophore-containing monomers for binary AND-type network formation: (a) light-stimulated deprotection of α-methyl­benzaldehyde (MBA) with subsequent light-induced enolization to activate it for a Diels–Alder cycloaddition (DA-CA) with maleimide (MI) as a universal reaction partner and (b) light-gated DA-CA of spiropyran in its open form with MI . Uncatalyzed light-initiated step-growth through chromophore-containing monomers for multi-material AND+OR-type photosensitive resins: (c) DA-CA of MBA and MI and/or nitrile imine tetrazole–ene CA of a tetrazole-based chromophore with MI and (d) two DA-CAs, which occur independently from each other at two wavelengths, with a pyrene- and an MBA-based chromophore. , Uncatalyzed light-initiated step-growth through chromophore-containing monomers for multi-material OR-type network formation: (d) as explained previously and (e) CA of a cis – trans reactivity-gated azobenzene and a reversibly photogenerated ketene …”

“…The use of a protected photoenol, which can be deprotected at one wavelength and reacted with a maleimide at a second wavelength, was a first step toward a synergistic chromophore-based reactive system (Scheme 2B,a). 28 More recently, we have introduced an uncatalyzed synergistic pair of photoactive compounds consisting of an azobenzene and a ketene of which, however, the reversibility is insufficient for a printing process at room temperature (Scheme 2B,e). 7 Dual-wavelength irradiation alone, however, is not a sufficient criterion to meet the synergistic conditions.…”

“… b Uncatalyzed light-initiated step-growth through chromophore-containing monomers for binary AND-type network formation: (a) light-stimulated deprotection of α-methyl­benzaldehyde (MBA) with subsequent light-induced enolization to activate it for a Diels–Alder cycloaddition (DA-CA) with maleimide (MI) as a universal reaction partner and (b) light-gated DA-CA of spiropyran in its open form with MI . Uncatalyzed light-initiated step-growth through chromophore-containing monomers for multi-material AND+OR-type photosensitive resins: (c) DA-CA of MBA and MI and/or nitrile imine tetrazole–ene CA of a tetrazole-based chromophore with MI and (d) two DA-CAs, which occur independently from each other at two wavelengths, with a pyrene- and an MBA-based chromophore. , Uncatalyzed light-initiated step-growth through chromophore-containing monomers for multi-material OR-type network formation: (d) as explained previously and (e) CA of a cis – trans reactivity-gated azobenzene and a reversibly photogenerated ketene …”

A Review of Multi-Material 3D Printing of Functional Materials via Vat Photopolymerization

“…Alves et al utilized di-thioacetal-protected aldehyde groups in combination with oMBA to orthogonally induce deprotection of monomers along with the activation of oMBA by using visible light and UV light in a sequential manner. After activation, oMBA formed o-quinodimethane, which further underwent a thermally-induced [4π + 2π] cycloaddition reaction with suitable electron deficient dienophiles such as N-ethylmaleimide [392]. O-methyl benzaldehydes, N-ethyl-maleimides, and styrylpyrene groups have shown orthogonal reaction approaches with thermo-activated [4π + 2π] Diels-Alder chemistry [364].…”

Divergent Synthesis of Graft and Branched Copolymers through Spatially Controlled Photopolymerization in Flow Reactors

“…More recently, the synthesis of tailored macromolecular products has been rationalized via one-step batch approaches through exploiting chemoselective reactions . In these cases, multistep reactions are performed either sequentially or concurrently in a single pot through the careful selection of multiple noninterfering reactions; these reactions are said to be performed orthogonally. − For instance, polymerizations and polymer postmodifications have been performed in a single pot by exploiting orthogonal reactions that are activated under different external stimuli, including heat, − light, − pH changes, other chemical concentration changes, , electrochemistry, or combinations thereof. The ability to independently control multiple reactions externally reduces the necessity for tedious isolation and handling steps and thus allows the desired product to be attained in a more straightforward manner. − Although the systems developed to date demonstrate elegant chemistry, there is still a great need for expansion to increase their versatility and applicability.…”