Picric acid sensing and ${\text{CO}}_2$ 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, ${}^i$PrTAPB-Azo-COP, has been synthesized by Cu(I) catalysed homo coupling (amine-amine) reaction of 1,3,5-tris($4^{\prime }$-amino-$3^{\prime },5^{\prime }$-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 ${\text{m}}^2$ g${}^{-1}$ with a pore diameter of 11.6 Å. 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 ${\text{CO}}_2$-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 ${\text{CO}}_2$ uptake of 6.5 and 19.4 wt% at 1 bar and 30 bar, respectively, at 273 K.

Graphical Abstract

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 ${\text{CO}}_2$ capture. .