A 3D Synthesis Strategy for Pyrene-Based Fluorescent Conjugated Polymers and Application in Picric Acid Sensing
Authors: Xu Jiaqiang , Fan Yu , An Baoli 
Published: May 2020

In this work, 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) was synthesized and used as polymer precursor, and then two kinds of fluorescent conjugated polymers (CPs) are synthesized through Schiff base reactions with two kinds of tri-amine as the other part of precursor, namely CPshu-1 and CPshu-2, respectively. By using D2h symmetry tetra-aldehyde and C3 symmetry tri-amine as precursors, aggregation-caused quenching (ACQ) of fluorophore can be reduced to minimum, to make the greatest fluorescent sensing performance. The resulting CPs were firstly characterized by Fourier transform infrared spectroscopy (FT-IR), solid-state 13C nuclear magnetic resonance (13C NMR). The morphology of resulting CPs were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fluorescent spectra indicated that the sample showed orange luminescene at around 610nm. Before detecting the sensing performance, the CPs were firstly dispersed into acetonitrile to make a 1 mg/mL suspension, and the suspension showed a high sensitive to picric acid (PA). The suspension of CPshu-1 was totally quenched at a PA concentration of 5.2×10-4 M, and the limit of detection was calculated to be 3.18 ppm. For CPshu-2, the suspension was totally quenched at a PA concentration of 3.5×10-4 M, and the limit of detection was calculated to be 2.11 ppm. This work demonstrated that we can design 3D polymer structure to avoid ACQ negative effects, and build high performance fluorescent chemosensing materials.

Introduction

Fluorescent chemosensors is a kind of sensors which is attracting increasing attention from scientists. Aromatic π-electron conjugated polymers(CPs) is a very important kind of organic polymers used as fluorescent chemosensors due to the advantages of signal amplification, ease of device fabrication and the ability to combine different outputs. Although there has been a fast progress in the development of fluorescent CPs, there are still great requirements on materials with high efficiency, low cost, and eco-friendly, and also the design strategy of building CPs should also be developed. Making use of AIE and ACQ phenomena can rationally and tactfully enhance the fluorescene performance and avoid unexpected quenching, resulting in increasing importance for design strategy of fluorescent CPs.
In this study 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) was used as fluorophore to build CPs through Schiff base reaction. The monomer of TFPPy was synthesized through a Suzuki coupling according to literature with a modified solvent condition. Two kinds of CPs named as CPshu-1 and CPshu-2, respectively, have been grown by solvothermal method using TFPPy as aldehyde monomer. The structures of both CPs were designed as 3D structure in which π-π stacking of fluorophores were avoided, decreasing the ACQ phenomenon to the minimum. The formation of CPs from the condensation reactions of the monomers was supported by FT-IR and 13C NMR spectra. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated the rod-like morphology of resulting CPs, which could also prove the non-stacking structure of aromatic fluorophores. Furthermore the CPs were dispersed into acetonitrile and the suspension was used to detect picric acid. Both suspensions of CPshu-1 and CPshu-2 showed great chemical sensitive to picric acid, and the limit of detection (LOD) was 3.18ppm for CPshu-1, and 2.11ppm for CPshu-2, respectively.

Figure 1