# Hidden Structural Colors from Bistable, Electrically Driven Covalent Organic Framework Photonic Assemblies for Secure Optical Encoding

## TL;DR

This paper introduces a secure optical encryption system using electrically controlled covalent organic framework particles that hide and reveal data under specific viewing conditions.

## Contribution

A novel bistable, electrically driven COF-based photonic system for secure optical encoding with tunable concealment via surface roughness.

## Key findings

- COF particles enable dynamic and bistable optical encryption under bright-field microscopy.
- Surface roughness controls concealment and transforms scattering into a security feature.
- The system offers compact, multifactor encryption for secure displays and anticounterfeiting.

## Abstract

Optical encryption using nanostructured materials provides
a powerful
route for secure data encoding. In this work, an electrically reconfigurable
colloidal photonic platform based on covalent organic framework (COF)
particles is described, enabling dynamic and bistable data encryption.
Spatially controlled electrophoretic assembly of monodisperse COF
particles within patterned cells produces Bragg reflections that are
visible only under bright-field (BF) microscopy as strong broadband
scattering from nanoscale particle surface roughness conceals the
encoded states from the naked eye. By tuning the synthesis time, the
particle surface roughness and, thus, the degree of concealment can
be precisely controlled. Unlike conventional optical systems, where
scattering degrades visibility, we report it as an intrinsic security
feature, transforming a loss mechanism into a tool for optical masking.
The demonstrated platform combines electrical addressability, conditional
optical visibility, and algorithmic decoding to deliver a compact,
multifactor encryption system. These results demonstrate colloidal
COF dispersions as a versatile class of photonic materials for secure
displays, anticounterfeiting, and adaptive optical communication technologies.