# Deconvoluting the Optical Response of Biocompatible Photonic Pigments

## TL;DR

This paper introduces biocompatible photonic pigments made from block copolymers that can produce vibrant colors while addressing environmental concerns.

## Contribution

The novel contribution is the use of inverse photonic glass architecture with biocompatible BBCPs to achieve strong optical responses.

## Key findings

- Biocompatible BBCPs can be tuned for color via molecular weight or processing temperature.
- An analytical scattering model and FDTD simulations reveal the structure-optic relationship.
- Strategies to enhance color purity are proposed and demonstrated using the BBCP system.

## Abstract

To unlock the widespread use of block copolymers as photonic pigments, there is an urgent need to consider their environmental impact (cf. microplastic pollution). Here we show how an inverse photonic glass architecture can enable the use of biocompatible bottlebrush block copolymers (BBCPs), which otherwise lack the refractive index contrast needed for a strong photonic response. A library of photonic pigments is produced from poly(norbornene‐graft‐polycaprolactone)‐block‐poly(norbornene‐graft‐polyethylene glycol), with the color tuned via either the BBCP molecular weight or the processing temperature upon microparticle fabrication. The structure–optic relationship between the 3D porous morphology of the microparticles and their complex optical response is revealed by both an analytical scattering model and 3D finite‐difference time domain (FDTD) simulations. Combined, this allows for strategies to enhance the color purity to be proposed and realized with our biocompatible BBCP system.