Triptycene based fluorescent polymers with azo motif pendants: Effect of alkyl chain on fluorescence, morphology and picric acid sensing

A design and synthesis of three unique triptycene based polymers containing azo linkages in the side chain of polymer backbone is being reported herein for the first time. These triptycene based azo-polymers (TBAPs) have high solubility in common organic solvents due to the presence of pendent alkyl chains as well as triptycene motifs. TBAPs are well characterized by GPC, TGA, ¹H NMR, FTIR, PXRD, FESEM, UV and fluorescence spectroscopy. Polymers with azo-linkages are generally non-fluorescent. However, TBAPs are fluorescent in nature which makes them unique. It was observed that TBAP3 having the longest pendent alkyl chain is most fluorescent when compared with TBAP1 and TBAP2 (which have smaller pendent alkyl chains). Furthermore, TBAPs have been applied for the detection of trace quantities of PA in THF. The binding constants of TBAPs with PA are in the order of 10⁵ M⁻¹ and the PA can be detected even in nanomolar concentrations. It was observed that TBAP1 having the smallest pendent alkyl chain has the highest binding affinity for PA relative to TBAP2 and TBAP3 (having longer pendent alkyl chains). Further, the effect of the chain length on the supramolecular assembly of these polymers was observed using FESEM. The size of domains present in polymer films was found to increase with increasing chain length of alkyl group.