A Substitution‐Dependent Light‐Up Fluorescence Probe for Selectively Detecting Fe³⁺ Ions and Its Cell Imaging Application

Abstract Deliberate design of specific and sensitive molecular probes with distinctive physical/chemical properties for analyte sensing is of great significance. Herein, by taking advantage of the position‐dependent substituent effects, an aggregation‐induced emission featured iron (III) probe from ortho ‐substituted pyridinyl‐functionalized tetraphenylethylene (TPE‐ o ‐Py) is synthesized. It displays high sensitivity and selectivity toward iron (III) detection. The recognition arises from the position isomer of ortho ‐substitution, and the fact that TPE‐ o ‐Py has a low acid dissociation constant (p K a ) that is close to that of hydrolyzed Fe 3+ . Importantly, TPE‐ o ‐Py as a light‐up fluorescence probe could be employed for Fe 3+ sensing in living cells with a pronounced red‐shift in fluorescence emission.