Abstract
In the past, plasma polymers have never demonstrated good light-emitting properties. By using continuous-wave (CW) r.f. plasma, light-emitting polymers in the form of thin films and powders of high quantum efficiency were synthesized from 1-naphthaldehyde (35%) and 1-ethylnaphthalene (46%) and by plasma polymerization. The very high vapor density directly introduced into plasma region without carrier gas to achieve very high deposition rate. On the other hand, the substituent can prevent the conjugated structure from fragmentation process during plasma polymerization. The 1-naphthaldehyde monomer absorbs strongly in the UV but emits no light, apparently due to inter-system crossing influenced by the carbonyl groups. Extensive aldehyde and ethyl groups cleavage along with partial ring opening during plasma polymerization resulted in polymers that fluoresced strongly in the range of blue light with a lifetime around 35 ns. Large Stokes shift observed in plasma polymers attributed to Főster Resonance Energy Transfer (FRET) mechanism between different chromophores due to the random nature of plasma discharge. According to FTIR, XPS and PL spectrum, the 3-D tandem-like microstructure is constructed by isolated naphthalene-type and benzene-type chromophores interconnected by polyene and soft alkyl backbones and the conjugated structures could be preserved efficiently. In the degradation experiment, the plasma thin films also show well stability comparative to MEH-PPV. By well-selected reaction parameters and properly designed monomer structures, light-emitting polymer powders or in-situ coated light-emitting polymer thin films could easily be synthesized and the color of fluorescence could be tunable. Light-emitting polymers of high quantum efficiency and good stability were obtained, signifying the possibility of this method to impart light-emitting properties onto designated surfaces. The fast deposition rate and one-step reaction could enormously cost down in mass productions.