Fluorescence properties of poly(ethylene terephthalate-co-2,6-naphthalene dicarboxylate) with naphthalene contents ranging from 0.01 to 100 mol %

Several samples of poly(ethylene terephthalate-co-2,6-naphthalene dicarboxy late) were synthesized with different contents of dimethyl-2,6-naphthalene dicarboxylate (DMN). The polymer samples were ground into powders, and stea dy-state and time-resolved fluorescence measurements were carried out on th ese copolymers. The lifetimes of the excited DMN monomer and dimer were fou nd to be 12 and 26.5 ns, respectively. By monitoring the overlap between th e fluorescence excitation and emission spectra of the different species, it was concluded that energy migration occurs among the DMN monomers and amon g the DMN dimers, that energy can be transferred from an excited DMN monome r to a groundstate DMN dimer, but that energy transfer from an excited DMN dimer to a ground-state DMN monomer is unlikely. Increasing the DMN content induces the formation of energy traps for the DMN monomer fluorescence, wh ich results in increasing DMN monomer quenching. When the DMN content reach es 25 mol %, the polymer matrix is saturated with DMN dimers, and no furthe r quenching is observed.