Synthesis through Continuous-Wave Plasma of High Quantum Efficiency Light-Emitting Polymers from 1-Naphthaldehyde

By using continuous-wave (CW) r.f. plasma, light-emitting polymers of high quantum efficiency (35{\%}) were synthesized from 1- naphthaldehyde. The monomer absorbed strongly in the UV but emitted no light, apparently due to the inter-system crossing influenced by the carbonyl groups. Extensive aldehyde cleavage and partial ring opening during plasma polymerization resulted in polymers that fluoresced strongly in the range of 422 -- 455 nm with a lifetime around 35 ns. Relative to the naphthalene chromophore, the plasma polymers illustrated a large red-shift (100 -- 120 nm) in emission but showed no shifting in absorption which peaked at 277 nm. A chain microstructure constructed by isolated naphthalene-type chromophores interconnected by soft alkyl backbones was proposed for the plasma polymers in which vibronic interactions between the excited chromophores and soft alkyl chains were used to explain the large Stokes shift observed.