# Theoretical and experimental studies of photomechanical materials

## TL;DR

This paper develops a comprehensive theory and experimental methods to analyze the photomechanical response of light-responsive materials, focusing on mechanisms like photothermal heating and photo-isomerization, and introduces the concept of photomorphons.

## Contribution

It presents a unified theoretical framework, experimental apparatus, and the concept of photomorphons for understanding and measuring photomechanical effects in materials.

## Key findings

- Characterized various materials to isolate mechanisms.
- Defined efficiency and figure of merit for photomechanical response.
- Introduced the photomorphon as a fundamental material element.

## Abstract

After a brief introduction to the field of light-responsive materials, this paper provides a general theory for modeling the photomechanical response of a material, applies it to the two best-known mechanisms of photothermal heating and photo-isomerization, and then describes an experimental apparatus for quantitative measurements of the stress response. Several different materials are characterized to illustrate how the experiments and theory can be used to isolate the contributing mechanisms both through photomechanical measurements and auxiliary measurements of laser heating and thermal expansion. The efficiency and figure of merit of the photomechanical response is defined on several scales form the molecule to the bulk, and the photomorphon -- the basic material element that determines the bulk response -- is introduced. The photomorphon provides a conceptual model that can be expressed in terms of viscoelastic elements such as springs in series and parallel with the photoactive molecule. The photomechanical response, figure of merit, and the deduced microscopic photomechanical properties are tabulated and proposals for new materials classes are made.