# Advances in pH‐Sensitive Luminescent Transition Metal Complexes for Theranostic Applications

## TL;DR

This paper reviews recent progress in pH-sensitive luminescent metal complexes for sensing and cancer treatment.

## Contribution

The first comprehensive review connecting luminescence modulation with theranostic function in pH-sensitive transition metal complexes.

## Key findings

- pH changes significantly affect luminescence through protonation and charge-transfer processes.
- Ruthenium(II) complexes are highlighted for their tunable properties and suitability in biological environments.
- Design strategies for reliable pH sensing and imaging are outlined based on mechanistic insights.

## Abstract

pH sensitive luminescent transition metal complexes are emerging as next generation molecular probes for sensing, bioimaging, and cancer theranostics. Small variations in protonation state can markedly influence their photophysical behavior by modulating charge‐transfer processes, excited‐state energetics, and noncovalent interactions, resulting in pronounced and often reversible changes in emission intensity or wavelength. In this review, we examine recent advances in the design of pH‐responsive luminescent transition metal complexes and discuss the mechanistic origins of their pH sensitivity, including protonation‐deprotonation equilibria, hydrogen‐bonding effects, and aggregation‐induced phenomena. Particular emphasis is placed on ruthenium(II) and related complexes, which offer long‐lived excited states, structural robustness, and wide tunability through rational ligand design. We critically analyze representative systems across different metal platforms with respect to their pKa ranges, emission responses, and suitability for biological environments. By highlighting both recent progress and existing limitations, we aim to clarify design strategies that are most likely to translate into reliable tools for real‐time pH sensing, high‐resolution imaging, and multifunctional theranostic applications.

This first comprehensive review unifies recent developments in pH‐sensitive luminescent transition metal complexes, outlining mechanistic insights that connect luminescence modulation with theranostic function and inspire future design strategies.