# Photoswitchable Active Esters for the Control of Amide Bond Formation with Light

## TL;DR

This paper introduces light-sensitive chemical reagents that allow precise control over amide bond formation using light.

## Contribution

The development of photoswitchable active esters that enable light-controlled amide bond formation.

## Key findings

- Photoswitchable active esters show up to 24-fold enhancement in aminolysis rate in their closed isomer state.
- Light-induced modulation was applied to dye labeling, polymer gelation, and thin film patterning.
- Reversible control was achieved using 365 nm light for activation and 625 nm for inhibition.

## Abstract

Active esters are among the most utilized reagents for
(bio)­materials
functionalization via amide bond formation. To endow this type of
ligation processes with spatiotemporal precision, we herein report
the development of photoswitchable active esters, which toggle between
poorly and highly reactive states upon irradiation with UV and visible
light. Specifically, a dithienylethene photoswitch was introduced
within the structure of common p-nitrophenyl active
esters, whose electronic changes upon reversible open-closed photoisomerization
turn on and off the activating effect of the p-nitro
substituent on amidation reactivity. As a result, efficient light-induced
modulation of amide bond formation kinetics was accomplished with
these compounds, with their closed isomer exhibiting up to 24-fold
enhancement of aminolysis rate with amines relative to the open state.
This behavior was exploited to reach reversible light-control of illustrative
examples of amidation-based ligation processes: dye labeling, polymer
gelation and polymer thin film patterning, which was selectively triggered
by illumination at 365 nm and inhibited by irradiation at 625 nm.
These results demonstrate the potential of photoswitchable active
esters to provide enhanced spatiotemporal control to the functionalization
and manipulation of molecules and materials.