Synthesis and fluorescence of polyurethane cationomers N-modified with a stilbene chromophore

Preparation of a polyurethane cationomer with stilbene chromophore on urethane nitrogen atoms was performed by stepwise modification of a neutral polymer (PU-S1, stilbene units: 13.6 wt.%), followed by the quaternization with benzyl chloride (PUC-S1, 34.8 meq. ionic groups/100 g polymer). A linear polyesterurethane based on poly(ethylene adipate) diol (Mn: 2000), 4,4′-methylene-bis(phenyl isocyanate), 1,4-butanediol and N-methyldiethanolamine (1:6:3:2 molar ratio) was used as precursor. The trans–cis photoisomerism and fluorescent emission of the stilbene in polycation was studied and compared with the non-ionomeric form and the urethane-stilbene derivative. Another cationomer with fluorophore introduced via quaternization of the same precursor with urethane-stilbene halide was also taken in study (PUC-S2, 39.7 meq. ionic groups/100 g polymer). All polymers absorb in the UV region (λA: 313–332 nm) and reemit the light as violet–blue fluorescence in the region 420–470 nm. The significant red shift of the emission band in both polymer solution and film was assigned to the formation of excimers between fluorophores.