# Arylpyrrolylidene-indanones as readily synthesised photoswitches offering dual- and single-colour fluorescence toggling with nearly quantitative E/Z isomerisation under visible light

## TL;DR

This paper introduces new light-sensitive molecules that can switch fluorescence colors using visible light, with potential uses in imaging and data storage.

## Contribution

A new class of visible-light-responsive arylpyrrolylidene-indanone photoswitches with high-intensity dual- and single-color fluorescence toggling is introduced.

## Key findings

- The compounds exhibit nearly quantitative E/Z isomerization under visible light.
- The Z-isomer achieves a fluorescence quantum yield of 0.5 due to an intramolecular hydrogen bond.
- These photoswitches are fatigue-resistant and suitable for biological and material applications.

## Abstract

Super-resolution fluorescence imaging and ultrahigh-density optical data storage, in particular, rely on the switches that demonstrate single- or (multi) dual-colour fluorescence toggling, with the latter option being more advantageous. However, a large number of switches are non-emissive owing to their fast photoisomerisation. Also, many fluorescent switches suffer from the necessity of high-energy UV light irradiation, low isomerisation yields, photodegradation, or the comparatively low fluorescence quantum yields. Herein, we present a new class of visible-light-responsive novel arylpyrrolylidene-indanone switches that permit high-intensity dual-colour fluorescence switching and quantitative photoisomerisation between exceptionally thermally stable E- and Z-isomers. The presence of an intramolecular hydrogen bond (–C

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O⋯H–N) renders the Z-isomer significantly more emissive, achieving a quantum yield (Qf) of 0.5. These photoswitches are highly fatigue resistant and additionally display solvent viscosity-dependent fluorescence emission by the E-isomers as well. By speeding up the rotation of a C–C bond between pyrrole and CC with the addition of two large substituents at sp3-C, guided by the DFT calculations, the emission of the E-isomer is almost completely lost, making these compounds single-colour (on/off) fluorescent photoswitches. Fluorescence photoswitching in 50% DMSO-PBS buffer works well, revealing the potential of these switches for biological applications, as well as for material uses.

Visible-light-responsive arylpyrrolylidene-indanones enable single- and dual-colour fluorescence photoswitching with (near) quantitative E/Z isomerization between two thermally stable photoisomers.