Picric acid sensing and CO2 capture by a sterically encumbered azo-linked fluorescent triphenylbenzene based covalent organic polymer

A sterically encumbered isopropyl group substituted fluorescent triphenylbenzene based azo-linked covalent organic polymer, iPrTAPB-Azo-COP, has been synthesized by Cu(I) catalysed homo coupling (amine-amine) reaction of 1,3,5-tris(4'-amino-3',5'-isopropylphenyl) benzene ((i)PrTAPB) under aerobic conditions. The Brunauer-Emmett-Teller (BET) and Langmuir surface areas of (i)PrTAPB-Azo-COP have been estimated to be 395 and 697 m(2) g(-1) with a pore diameter of 11.6 angstrom. Due to the presence of fluorescent triphenylbenzene platform (i)PrTAPB-Azo-COP exhibits broad emission band centred at 428 nm, when excited at 300 nm, as a result of extended conjugation. The inherent fluorescent nature of (i)PrTAPB-Azo-COP has been utilized for sensing electron-deficient polynitroaromatic compounds (PNACs) such as a picric acid (PA), dinitrotoluene (DNT), p-dinitrobenzene (p-DNB) and m-dinitrobenzene (m-DNB). Further, (i)PrTAPB-Azo-COP has also been utilized for capture of carbon dioxide as the azo-COP is enriched with CO2-philic nitrogen atoms apart from its microporosity. Since the azo (-N=N-) linkages are masked by the bulky isopropyl groups, (i)PrTAPB-Azo-COP exhibits a CO2 uptake of 6.5 and 19.4 wt% at 1 bar and 30 bar, respectively, at 273 K.