# Synergistic Two‐Color Photochemical Polymer Network Formation and Lithography

## TL;DR

This paper introduces a new two-color lithography method using light to control polymer network formation for advanced 3D printing.

## Contribution

The novel approach uses two photoswitches activated by different wavelengths to enable synergistic crosslinking and precise spatial control.

## Key findings

- Simultaneous irradiation at 375 and 430 nm triggers covalent crosslinking, while single-wavelength exposure does not.
- The method allows fabrication of complex structures like segmented rings and butterflies using dual-laser lithography.
- Kinetic analysis shows the potential of synergistic activation for advanced additive manufacturing.

## Abstract

We introduce synergistic two‐color lithography as an advanced wavelength‐gated strategy for spatially and temporally controlling polymer network formation. Our photoresist entails two photoswitches, i.e., diarylindenone epoxide (DIO) and strained azobenzene (SA), each activated at a judiciously selected wavelength, i.e., 375 or 430 nm. Under specific conditions of photon flux, simultaneous irradiation at both wavelengths induces a (3 + 2) cycloaddition between the photoactivated DIO′ and SA′ species, generating covalently crosslinked networks, whereas under these specifically determined conditions, single‐wavelength exposure does not induce solidification. Kinetic analysis highlights the potential of synergistic activation to enable advanced additive manufacturing. We implemented the two‐color activated covalent bond forming system in a dual‐laser lithographic platform enabling the fabrication of well‐defined structures, including segmented ring and butterfly architectures by simply activating and deactivating one of the colors of light.

Two photoswitches, able to respond to disparate wavelengths, are integrated into multi‐functional polymer architectures to form a photoresist that responds to curing upon irradiation with two distinct monochromatic colors of light, enabling two‐color lithography.