Picric acid sensing and $$\hbox {CO}_{2}$$ CO 2 capture by a sterically encumbered azo-linked fluorescent triphenylbenzene based covalent organic polymer

Abstract

A sterically encumbered isopropyl group substituted fluorescent triphenylbenzene based azo-linked covalent organic polymer, $$^{i}$$ PrTAPB-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 $$\hbox {m}^{2}$$ g $$^{-1}$$ with a pore diameter of 11.6 A. 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 $$\hbox {CO}_{2}$$ -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 $$\hbox {CO}_{2}$$ uptake of 6.5 and 19.4 wt% at 1 bar and 30 bar, respectively, at 273 K. SYNOPSIS Sterically encumbered azo-linked covalent organic polymer ( $$^{i}$$ PrTAPB-Azo-COP) has been synthesized from a fluorescent hexaisopropyl substituted triphenylbenzene platform. The resulting fluorescent porous COP has been utilized for picric acid sensing and $$\hbox {CO}_{2}$$ capture.