Single‐Benzene Fluorophores: Controlling Electron Density on Amino of 2,5‐Diaminoterephthalates to Manipulate Optical/Electronic Properties for Efficient and Diversified Functions

Abstract Single‐benzene fluorophores have attracted increasing interest owing to their simple molecular structure and unique photophysical properties. Developing novel single‐benzene fluorophores with facile synthesis, bright and tunable dual‐state emissions, and diversified functions is highly desirable. Herein, a strategy of controlling electron density on amino of 2,5‐diaminoterephthalates is proposed to modulate their dual‐state emission, acidichromism, Cu 2+ detection, and lipid droplets (LDs) staining. A series of efficient dual‐state single‐benzene fluorophores based on 2,5‐diaminoterephthalate skeleton with tunable emissions in blue to red region and large Stokes shifts is facilely developed. The obtained fluorophores with various substituents on amino groups exhibit different acidichromism property. Two of fluorophores (ABB and ABM) with high electron density on amino groups exhibit high sensitivity and selectivity toward Cu 2+ detection with a ratiometric and “turn‐off” fluorescence mechanism for ABM and ABB, respectively. The limit of detection for Cu 2+ is determined to be 1.40 × 10 −7 and 4.35 × 10 −9 mol L −1 for ABB and ABM, respectively. Moreover, three of fluorophores (ABT, ABB, and ABM) with green to red emission display superior LDs‐targeting capability with high specificity, and brightness. This molecular design philosophy provides a new way of designing highly bright dual‐state fluorophores for practical applications.