A dual-function naphthalimide derivative for Cr(VI) detection and supramolecular room-temperature phosphorescence.

A functional fluorescent molecule, 4-bromo-1,8-naphthalimide derivative (BN1B) was designed and synthesized and used as a fluorescent probe for detecting Cr(VI) in aqueous media. The fluorescence intensity of BN1B decreased with increasing Cr(VI) concentration, and the detection limits were 3.64 × 10⁻⁶ mol·L⁻1 for CrO₄2⁻ and 2.98 × 10⁻⁶ mol·L⁻1 for Cr₂O₇2⁻. Moreover, a distinct fluorescence color change was observed for BN1B solutions containing CrO₄2⁻ or Cr₂O₇2⁻ under 356 nm UV irradiation, producing pale yellow and orange yellow emissions, respectively. The probe features simple preparation, low cost, fast response, and high sensitivity. Exploiting the favorable optical properties of BN1B, a supramolecular assembly, BN1B@Q[8], was constructed with cucurbit[8]uril (Q[8]). In this assembly, the benzene rings and part of the naphthalene moiety of BN1B are encapsulated by Q[8], forming a 2:1 host-guest inclusion complex. Furthermore, a film was prepared by incorporating BN1B@Q[8] into a polyvinyl alcohol (PVA) matrix at a mass ratio of 1:50. The film effectively isolated the assembly from atmospheric oxygen and moisture, suppressed non-radiative transitions, and induced long-lived room-temperature phosphorescence with a lifetime τ = 55.19 ms. The use of this phosphorescent film in anti-counterfeiting highlights its potential for expanding applications of luminescent materials in encryption and related fields.