A tetraphenylethene-substituted pyridinium salt with multiple functionalities: synthesis, stimuli-responsive emission, optical waveguide and specific mitochondrion imaging

Na Zhao,Yi Lin Zhang,Ben Zhong Tang,Yongli Yan,Kam Sing Wong,Jacky W Y Lam,Min Li,Yong Sheng Zhao

doi:10.1039/c3tc30759j

Abstract

In this work, a heteroatom-containing luminogen (TPE-Py) with multi-functionalities was synthesized in a reasonable yield by melding a pyridinium unit with tetraphenylethene through vinyl functionality. TPE-Py is weakly emissive in solution but becomes a strong emitter when aggregated as nanoparticle suspensions in poor solvents or in the solid state, displaying a phenomenon of aggregation-induced emission. Crystallization generally weakens and red-shifts the light emission. The crystalline aggregates of TPE-Py, however, emit stronger and bluer light than their amorphous counterparts. The solid-state emission of TPE-Py can be reversibly switched between green and yellow color by grinding–fuming and grinding–heating processes with a high contrast due to the transformation from the crystalline to the amorphous state and vice versa. The large Stokes shift and well-ordered molecular arrangement of the crystalline microrods of TPE-Py make it promising as an optical waveguide material with a low optical loss coefficient of ∼0.032 dB μm−1. TPE-Py works as a good fluorescent visualizer for specific staining of mitochondria in living cells with a high photostability, thanks to its hydrophobic and cationic features.

Highlights

Development of new materials with advanced functionalities is a crucial step for future technological innovations
TPE-Py was synthesized according to the synthetic route shown in Scheme 1.17 1,4-Dimethylpyridinium iodide (1) and 4-(1,2,3triphenylvinyl)benzaldehyde (2) were prepared by the synthetic procedures as shown in Scheme S1 in the Electronic supplementary information (ESI)† and heated under re ux in ethanol, which gave TPE-Py in a reasonable yield a er counter anion exchange and puri cation by column chromatography
When the measurements are carried out in other solvents with increasing polarity, the emission spectrum moves to the longer-wavelength region accompanying with a decrease in the emission intensity (Fig. S2†), which is demonstrative of an intramolecular charge transfer (ICT) effect caused by the interaction between the electron-donating TPE unit and the electron-accepting pyridinium moiety.[4]

Summary

Introduction

Development of new materials with advanced functionalities is a crucial step for future technological innovations. Based on theoretical and experimental studies, the restriction of intramolecular rotation (RIR) is considered to be the main cause for the AIE phenomenon.[7] Since AIE luminogens are highly emissive in the aggregated state, this unique characteristic differentiates them from conventional luminophores and makes them promising materials for high-technological applications in the practically useful solid state.[8] As a result, various AIE dyes have been developed and their utilities in many elds such as organic light-emitting diodes,[9] bioprobes,[10] chemosensors[11] and cell imaging[12] have been explored, thanks to the enthusiastic efforts of the scientists.

Results

Conclusion