Tetraphenylethene-Modified Colorimetric and Fluorescent Chemosensor for Hg2+ With Aggregation-Induced Emission Enhancement, Solvatochromic, and Mechanochromic Fluorescence Features

Abstract

A tetraphenylethene (TPE)-modified rhodanine derivative was successfully designed and prepared, and this luminophor showed intramolecular charge transfer nature from the TPE unit to the rhodanine-3-acetic acid unit. Interestingly, this luminogen not only exhibited typical aggregation-induced emission enhancement (AIEE) behavior but also showed good cell imaging performance. Remarkably, this AIEE-active TPE-containing rhodanine derivative possessed noticeable solvatochromic fluorescence effect involving multiple fluorescent colors of green, yellow-green, yellow, orange, and red. Meanwhile, this fluorescigenic compound displayed reversible mechanochromic fluorescence behavior based on the mutual transformation of between stable crystalline and metastable amorphous states. On the other hand, this multifunctional fluorophor could selectively and sensitively detect Hg²⁺ in an acetonitrile solution. Furthermore, this chemosensor could also be used to detect Hg²⁺ on test paper strips.

Keywords: aggregation-induced emission enhancement; chemosensor; mechanochromic fluorescence; rhodanine; solvatochromic fluorescence.

GRAPHICAL ABSTRACT

An AIEE-active colorimetric and fluorescent chemosensor of Hg²⁺ was reported, and it exhibited good cell imaging, notable solvatofluorochromic and reversible mechanofluorochromic characteristics.

SCHEME 1

Synthesis of compound 1.

FIGURE 1

(A) Emissive spectra of the dilute solutions of compound 1 (concentration: 2.0 × 10⁻⁵ mol L⁻¹) in CH₃CN-H₂O mixtures with varying f _w values. (B) Changes in the emission intensity of 1 at 618 nm in CH₃CN-H₂O mixtures with varying f _w values (0–90%). (C) PL images of 1 (20 μM) in CH₃CN-H₂O mixtures with varying f _w values (0–90%) under 365 nm UV light.

FIGURE 2

Size distribution curve of compound 1 (2.0 × 10⁻⁵ mol L⁻¹) in CH₃CN-H₂O mixture with 90% water fraction.

FIGURE 3

The MTT assay of rhodanine derivative 1 for measuring cell viability.

FIGURE 4

Fluorescence images of HeLa cells incubated with rhodanine derivative 1 (20 μM) for 30 min at 37°C; from left to right are bright field image (A), fluorescence image (B), and merge image (C).

FIGURE 5

(A) Normalized fluorescence spectra (Excitation wavelength = 365 nm) of compound 1 (2.0 × 10⁻⁵ mol L⁻¹) in different solvents. (B) PL images of compound 1 (2.0 × 10⁻⁵ mol L⁻¹) in different solvents under 365 nm UV illumination.

FIGURE 6

(A) Fluorescence spectra of solid sample 1 before grinding, after grinding, after treatment with dichloromethane vapor. The excitation wavelength is 365 nm. Fluorescence images of sample 1 in various states under 365 nm UV light: (B) as-synthesized sample, (C) ground sample, (D) sample after treatment with dichloromethane vapor.

FIGURE 7

XRD patterns of compound 1 in different solid states: unground, ground, and after treatment with dichloromethane solvent vapor.

FIGURE 8

(A) The UV-Visible spectra of chemosensor 1 (concentration: 2.0 × 10⁻⁵ mol L⁻¹) in acetonitrile upon addition of 10 equiv. various metal ions. (B) Color changes of chemosensor 1 (concentration: 2.0 × 10⁻⁵ mol L⁻¹) in acetonitrile upon addition of 10 equiv. various metal ions.

FIGURE 9

(A) Fluorescence spectra of compound 1 (2.0 × 10⁻⁵ mol L⁻¹) in acetonitrile towards various cations. Excitation wavelength = 425 nm. (B) Fluorescence photographs of compound 1 (2.0 × 10⁻⁵ mol L⁻¹) in acetonitrile after addition of various metal ions (10.0 equiv.) under 365 nm UV light.

FIGURE 10

Photographs showing: (A) Fuorescent color changes of compound 1 on test paper strips after treating with various metal ions under 365 nm UV light. (B) Visible color changes of compound 1 on test paper strips after treating with various metal ions under natural light. (C) Fuorescent color changes of different concentrations of Hg²⁺ (2.0 × 10⁻⁵ mol L⁻¹) on test paper strips.