Emission properties of artificial opals infiltrated with a heteroaromatic quadrupolar dye

Artificial opals are a simple and cheap playground to manipulate the propagation of light. The interest in these kind of photonic crystals is further increased by the possibility to be infiltrated with highly polarisable media like organic semiconductors, i.e. conjugated polymers, push-pull molecules and multipolar chromophores. In this work, we report on the optical properties of polystyrene opals infiltrated with a heteroaromatic quadrupolar derivative endowed with strong nonlinear optical properties (two-photon absorption) in solution. The insertion of tris(ethylene glycol)monomethyl ether chains on the conjugated skeleton allows the molecule to be soluble in water, a non-solvent for polystyrene. This condition is fundamental in order to attempt opal infiltration. Variable angle transmittance and photoluminescence spectroscopy are used to characterize the system. The bathochromic shift of the opal stop band upon immersion in the chromophore solution confirms that the infiltration process easily takes place preserving a dielectric contrast suitable for further investigations. Photoluminescence spectra recorded at different emission angle with respect to the normal of the sample for both the chromophore solution and opals infiltrated with such solution show interesting characteristics. The presence of opal modifies the chromophore emission spectrum by filtering the light for wavelengths corresponding to those of the stop band and according to its dispersion