Ellipsometric analysis of the spectral properties and dynamic transitions of photochromic thin films

Solgel phenyl functionalized silica thin films were used as a host matrix to embed photochromic molecules (1,3,3,5,6-pentamethyl-spiro[indoline-2-3′-[quinolino]oxazine], 3-(2,4-dimethoxyphenyl)-3-(4-methoxyphenyl)-3H-naphtho[2,1-b]pyran and 3,3-diphenyl-3H-naphtho[2,1-b]pyran). The coatings were doped with individual dyes and mixtures of them. The optical properties of the colored and colorless forms of these photochromic materials were studied using variable angle spectroscopic ellipsometry. Light polarization analyses allowed an exhaustive ellipsometric characterization of these materials. Important changes were obtained in the refractive indices of the colored and colorless samples, with differences of up to 0.012 and 0.018 in the real and imaginary components, respectively. Good correlation was observed on the optical parameters of samples doped with individual dyes and mixtures of them. Standard transmission measurements were used to study the dynamic photochromic transitions and obtain the kinetic constants. The high capabilities of ellipsometry for the high-accuracy characterization of dynamic photochromic transitions were demonstrated. This technique allowed measuring variations in the populations of colored and colorless molecules, resulting from variations of temperature lower than ±0.1°C.