A smartphone-available colorimetric and near-infrared fluorescence sensor for trace amounts of water detection in highly polar organic solvents

In this work, we aimed to construct a sensitive and convenient sensor for trace amounts of water detection in highly polar organic solvents. We designed and synthesized four D-π-A structure sensors DTA-2QA-OH, TPA-2QA, TPA-2QA-OH, and TPA-4QA-OH by adjusting the electron donor and the linking site of the electron acceptor. The TPA-2QA-OH synthesized by connecting hydroxylated triphenylamine and quinolinium at position 2C can be used as a sensitivity sensor for trace amounts of water detection in highly polar organic solvents by using Na2HPO4 as a deprotonation reagent. TPA-2QA-OH can detect trace amounts of water in DMSO, MeOH, and EtOH in both colorimetric and near-infrared fluorescence modes. The significant color change of the sensing systems was captured by a smartphone and analyzed by using the PhotoMetrix APP to construct a standard curve between RGB values and water content in solvents. The detection limit of the sensor TPA-2QA-OH for trace amounts of water by using colorimetric, fluorescent, or smartphone methods were calculated as low as 0.0009% vol in DMSO, 0.0064% vol in MeOH, and 0.0014% vol in EtOH, respectively. For the first time, the influence of the connection site of quinolinium on the photophysical properties and detection performance of the sensor was found. The conjugation of the electron donor groups as well as the introduction of hydroxyl groups on the electron donor are important for the construction of D-π-A structure colorimetric and fluorescence ICT sensors for trace water detection in highly polar organic solvents.