Spectroscopic ellipsometry as a complementary tool for studying luminescent polymers: Poly(p-phenylenevinylene) as a particular case

Abstract

A novel approach for studying the thermal conversion of poly-p-xylylidene tetrahydrothiophenium chloride (PTHT) into poly(p-phenylenevinylene) (PPV) films has been proposed on the basis of calculated optical parameters. Spin-cast PTHT films were thermally converted into partially conjugated PPV films over conversion temperatures ranging from 22 C to 200 C. A strong correlation between refractive index (n) and damping constant extinction coefficient (k) was verified by spectroscopic ellipsometry (SE) for the films studied in the visible range of energy. The conversion temperature has a strong influence on the values of n and k, which were theoretically modeled using a Lorentz harmonic oscillator analysis. The films were also studied by spectroscopic techniques (photoluminescence, FTIR, and UVeVIS), and it was verified that the values of n decrease with increasing the amount of C]C groups present along the polymer chains, as a strong evidence that both structure and optical properties of thermally converted PPV films can be directly compared. The optical properties of the PPV films were also compared with those of two electroluminescent derivatives in which side chains are introduced into the phenyl ring of PPV, poly(2-methoxy-5-hexyloxy)-p-phenylenevinylene) (MH-PPV) and poly(3-methoxy-5-dodecyloxyp- phenyleneevinylene) (MD-PPV).