# Lewis Acid‐Triggered Spatiotemporally Controllable Ring Opening in a Classic Rhodamine Featuring Φ = 95% Emission

## TL;DR

A new method using Lewis acids to control rhodamine fluorescence improves brightness and stability without damaging the molecule.

## Contribution

A novel Lewis acid-triggered ring opening strategy for rhodamine fluorophores with high quantum yield and photocontrol.

## Key findings

- Lewis acid coordination enables reversible ring opening in rhodamine with up to 95% quantum yield.
- The method preserves molecular integrity while enhancing fluorescence performance.
- This approach offers spatiotemporal control and real-time tunability for advanced fluorescent materials.

## Abstract

Rhodamine derivatives, as a prominent class of fluorophores, have become indispensable in advanced material engineering and biomedical research due to their exceptional photostability and tunable optical characteristics. However, their practical implementation faces fundamental challenges: conventional proton‐mediated spirolactone ring opening mechanisms severely compromise fluorescence performance, while conventional structural optimization approaches remain synthetically demanding with limited efficacy. We hereby present a novel Lewis acid‐assisted activation strategy that enables reversible spirolactone ring opening in classical rhodamine systems. This innovative approach achieves remarkable fluorescence enhancement characterized by superior quantum yields (up to 95%) and prolonged excited state lifetimes. Notably, the Lewis acid coordination establishes precise photocontrol over the ring opening process. This breakthrough represents the first demonstration of a nondestructive activation pathway for rhodamine fluorophores, effectively converting the nonemissive spirolactone form into highly luminescent Lewis acid complexes while maintaining molecular integrity.

This work reports a breakthrough in rhodamine activation via an elegant Lewis acid coordination strategy. It induces ring opening in spirolactone rhodamine TMR, generating exceptional fluorescence (quantum yields up to 95%) without destructive modifications or structural modification. The method preserves full photocontrol, reversibility, and real‐time tunability, thereby paving the way for advanced fluorescent material design.© 2026 WILEY‐VCH GmbH