Optical response of phenantroimidazole-dyes covalently linked to a polynorbornene-backbone to acid and base

Two norbornene derivatives bearing phenantroimidazole dyes, namely endo/exo-11-(4-(1H-phenanthro[9,10-d]imidazol-2-yl)phenoxy) undecylbicyclo[2.2.1] hept-5-ene-2-carboxylat (5) and 11-(4-(1-Methyl-1H-phenanthro[9,10-d]imidazol-2-yl)phenoxy) undecylbicyclo[2.2.1]hept-5-ene-2-carboxylate (6) were synthesized. 5 and 6 were used to prepare statistical copolymers with endo,exo-bicyclo[2.2.1.]hept-2-ene-5,6-dicarboxylic acid dimethylester (7) via ring opening metathesis polymerization. The photophysical properties of the monomers and polymers and to what extent polymerization and substitution patterns influence the photophysical properties were investigated. Furthermore, the optical response upon addition of acid was investigated. The emission of monomer 5 shows a small bathochromic shift of 13 nm upon protonation while the emission of the resultant polymer poly5/7 exhibits a large red shift of 62 nm. In contrast, the according methylated monomer 6 and the resulting polymer poly6/7 gave similar absorption and emission characteristics. The differences were attributed to an increased tendency of the non-methylated dyes to interact when brought in close proximity in the polymer.