Fluorescent pH sensor constructed from a heteroatom-containing luminogen with tunable AIE and ICT characteristics

Zhiyong Yang,Herman H Y Sung,Ben Zhong Tang,Jacky W Y Lam,Ian D Williams,Sijie Chen,Wei Qin

doi:10.1039/c3sc50648g

Abstract

A heteroatom-containing organic fluorophore 1-(4-pyridinyl)-1-phenyl-2-(9-carbazolyl)ethene (CP3E) was designed and synthesized. CP3E exhibits the effect of intramolecular charge transfer (ICT) caused by the donor–acceptor interaction between its carbazole and pyridine units. Whereas it emits faintly in solution, it becomes a strong emitter in the aggregated state, demonstrating the phenomenon of aggregation-induced emission (AIE). Its emission can be reversibly switched between blue and dark states by repeated protonation and deprotonation. Such behaviour enables it to work as a fluorescent pH sensor in both solution and the solid state and as a chemosensor for detecting acidic and basic organic vapors. Analyses by NMR spectroscopy, single-crystal X-ray diffraction and computational calculations suggest that the change in electron affinity of the pyridinyl unit and molecular conformation of CP3E upon protonation and deprotonation is responsible for such sensing processes.

Highlights

Materials Tetrahydrofuran (THF) was distilled from sodium benzophenone immediately prior to use
Mixtures of CP3E in THF/water with various pH values were prepared by adding THF stock solutions into buffer solutions with specific pH values
High-resolution mass spectra (HRMS) were obtained from a GCT Premier CAB 048 mass spectrometer operated in MALDI-TOF or Cl-TOF mode

Summary

Experimental section

Materials Tetrahydrofuran (THF) was distilled from sodium benzophenone immediately prior to use. After filtration and solvent evaporation, the crude product was purified by silica gel column chromatography using hexane/ethyl acetate (4:1 v/v) as eluent to give 2.82 g (74%) of 4 as yellow-brown powder. The organic layers were collected and after solvent evaporation, the crude product was purified by silica gel column chromatography using hexane/dichloromethane (6:1 v/v) as eluent to give 0.95 g (45% yield) of CP3E as a light yellow powder. 1 mL of THF solution of CP3E (0.1 mM) was added dropwise into the above mixtures to furnish 10 μM solutions with defined fractions of water (fw = 0 90 vol %). For mixtures with 95 and 99 vol % water fractions, 0.1 mL of THF solution of CP3E with a concentration of 1 mM was used. Water acidified with hydrochloric acid (pH ~1) was used to prepare aqueous mixtures of CP3EH+

Refinement method

Findings

DM F etha nol acet onitrile