Development of optical sensor for water in acetonitrile based on propeller-structured BODIPY-type pyridine-boron trifluoride complex.

Shuhei Tsumura,Yousuke Ooyama,Kazuki Ohira,Keiichi Imato

doi:10.1039/d0ra06569b

Abstract

A propeller-structured 3,5,8-trithienyl-BODIPY-type pyridine–boron trifluoride complex, ST-3-BF3, which has three units of 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile at the 3-, 5-, and 8-positions on the BODIPY skeleton, was designed and developed as an intramolecular charge transfer (ICT)-type optical sensor for the detection of a trace amount of water in acetonitrile. The characterization of ST-3-BF3 was successfully determined by FTIR, 1H and 11B NMR measurements, high-resolution mass spectrometry (HRMS) analysis, thermogravimetry-differential thermal analysis (TG-DTA), photoabsorption and fluorescence spectral measurements, and density functional theory (DFT) calculations. ST-3-BF3 showed a broad photoabsorption band in the range of 600 to 800 nm, which is assigned to the S0 → S1 transition of the BODIPY skeleton with the expanded π-conjugated system over the 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile units at the 3-, 5-, and 8-positions onto the BODIPY core. In addition, a photoabsorption band was also observed in the range of 300 to 550 nm, which can be assigned to the ICT band between the 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile units at 3-, 5-, and 8-positions and the BODIPY core. ST-3-BF3 exhibited a characteristic fluorescence band originating from the BODIPY skeleton at around 730 nm. It was found that by addition of a trace amount of water to the acetonitrile solution of ST-3-BF3, the photoabsorption band at around 415 nm and the fluorescence band at around 730 nm increased linearly as a function of the water content below only 0.2 wt%, which could be ascribed to the change in the ICT characteristics due to the dissociation of ST-3-BF3 into ST-3 by water molecules. Thus, this work demonstrated that the 3,5,8-trithienyl-BODIPY-type pyridine–boron trifluoride complex can act as a highly-sensitive optical sensor for the detection of a trace amount of water in acetonitrile.

Highlights

Optical methods utilizing colorimetric and uorescent sensors for visualization as well as detection and quanti cation of water in samples and products, such as solutions, solids, and gases or water on substrate surfaces have been of considerable scienti c and practical concern in recent years, because of fundamental studies in photochemistry, photophysics, and analytical chemistry, and their potential applications to environmental and quality control monitoring systems and industry.[1,2,3,4,5,6,7,8,9] to date, some kinds of colorimetric and uorescent sensors for water based on ICT (intramolecular charge transfer),[10,11] PET (photo-induced electron transfer),[12,13] or ESIP (excited state intramolecular proton transfer)[14] have been designed and developed
Characterization of ST-3-BF3 The propeller-structured 3,5,8-trithienyl-BODIPY-type pyridine– BF3 complex ST-3-BF3 studied in this work was prepared by treating ST-3 with boron tri uoride diethyl etherate
For ST-3-BF3, the characteristic C]N stretching band of the pyridyl group coordinated to BF3, the B–N stretching band of the pyridine–BF3 complex, and the B–F stretching band of BF3 were clearly observed at 1636, 1429, and 1024 cmÀ1, respectively

Summary

Introduction

Optical methods utilizing colorimetric and uorescent sensors for visualization as well as detection and quanti cation of water in samples and products, such as solutions, solids, and gases or water on substrate surfaces have been of considerable scienti c and practical concern in recent years, because of fundamental studies in photochemistry, photophysics, and analytical chemistry, and their potential applications to environmental and quality control monitoring systems and industry.[1,2,3,4,5,6,7,8,9] to date, some kinds of colorimetric and uorescent sensors for water based on ICT (intramolecular charge transfer),[10,11] PET (photo-induced electron transfer),[12,13] or ESIP (excited state intramolecular proton transfer)[14] have been designed and developed. Paper a D–(p–A)2-type pyridine–BF3 complex YNI-2-BF3 composed of a carbazole skeleton as a donor moiety and two pyridine–BF3 units as acceptor moieties (Fig. 1a).11a It was found that the blueshi of the photoabsorption and the enhancement of the uorescence intensity in the low-water-content region could be attributed to the change in the ICT characteristics due to the dissociation of YNI-2-BF3 into the D–(p–A)2-type pyridine dye YNI-2 by water molecules.

Results

Conclusion