Plasmon activation and luminescence quenching of solutions of polyphenylene vinylene (MEH-PPV) by single-walled and double-walled carbon nanotubes

The spectral and luminescent properties of benzene and toluene solutions of poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with single-walled and double-walled carbon nanotube (CNT) additives are studied with the purpose of detecting the plasmonic properties of CNTs in the luminescence of MEH-PPV solutions. It is established that the dependence of the luminescence intensity of a solution of the polymer on the concentration of CNTs is nonmonotonic in nature; in particular, the luminescence intensity initially increases with an increase in the number of dissolved nanotubes and then decreases. In this case, the luminescence spectrum itself is barely deformed. This effect is observed with both single-walled CNTs (SWCNTs) and double-walled CNTs (DWCNTs). The depth of light intensity modulation in the case of DWCNTs was higher than in the case of SWCNTs. To explain the observed dependences, various versions of the electrodynamic model of exciting/quenching the luminescence of MEH-PPV by carbon nanotubes are proposed. Direct simulation of the characteristics of near and far fields is performed on the basis of Maxwell equations, for the numerical solution of which the finite difference time domain (FDTD) method is used. Computational experiments have shown that CNTs with a MEH-PPV layer have directional antenna properties and act as unusual waveguides. Thus, the energy of radiation that reached the far-field region in the nanotube axis direction is an order of magnitude higher than that in the case of a solution without CNTs. Fountain electromagnetic waves that emanate from both ends of the nanotube and the stage of plasmon wave beats, which characterizes the nanotube as a waveguide, are detected. Molecular dynamic simulation of the configurations of the adsorbed MEH-PPV chain in various solvents is performed both on an isolated CNT and on two parallel CNTs with different distances between them. It is found that the conformational structure of MEH-PPV becomes more and more loose as the distance between CNTs increases; in particular, an increase in the number of large loops of the macrochain in the bulk of the solution is observed.