Conjugated Microporous Polymer-Based Fluorescent Probe for Selective Detection of Nitro-explosives and Metal Nitrates

The sensitive and selective identification of nitroaromatic explosives and industrially ubiquitous nitrates, which are harmful to the environment, is crucial from the viewpoints of security and environmental remediation. New multifunctional fluorescent porous materials that can sense nitro-explosives and nitrates are under continuous development. To this end, this study synthesizes 3,10,15-/-3,10,16-tribromotrinaphtho[3.3.3]propellane (TBP) and 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,1,3-benzothiadiazole (BB) and employs them as dual building blocks to prepare a porous conjugated microporous polymer (denoted as CMP-TBP-BB) via Suzuki-Miyaura borylation polycondensation. The CMP-TBP-BB synthesis strategy takes advantage of the donor and acceptor characteristics of the propeller-like trinaphtho[3.3.3]propellane moiety in TBP and the benzothiadiazole group in BB, respectively. The unusual two-dimensional conformation of the CMP with propeller-array-structured monomers helps to position the π components in the crystalline layers and establishes aligned conduction pathways. CMP-TBP-BB exhibits outstanding fluorescence characteristics. Its distinctive two-dimensional skeleton is exploited to fabricate highly aligned donor-acceptor building blocks, which is typically considered a challenging task. The porous CMP acts as a fluorescent sensor for selectively and sensitively detecting electron-deficient nitro-explosives and metal nitrates. Specifically, CMP-TBP-BB is responsive to 2,4,6-trinitrophenol and Fe(NO₃)₃ at parts per million levels, and the results of combined experimental and theoretical investigations of its sensing properties highlight its potential as a CMP-based fluorescence probe. Additionally, the dual-function fluorescent CMP probe exhibits remarkable temperature-sensing behavior owing to the high linearity between the fluorescence intensity and temperature, making it an excellent fluorescent thermometer.