Second Harmonic Generation and Fluorescence of CMONS Dye Nanocrystals Grown in a Sol-Gel Thin Film

CMONS: an alternative to fluorescent probes? Nanocrystals of CMONS dye (see picture), about 100 nm in diameter, were grown in a sol‐gel thin film. The authors selectively grew the non‐centrosymmetric form in order to study the nanocrystals' nonlinear properties. Using scanning optical microscopy, the two‐photon induced fluorescence and the second harmonic generation (SHG) signals. (shown) were simultaneously mapped. Time‐resolved fluorescence spectroscopy on a single nanocrystal yielded an excited‐state relaxation time that is about twenty times smaller than that of a microcrystal, taken as the reference for bulk. This can be explained by the photoinduced isomerization of the stilbene‐like CMONS molecules localized at the surface of the nanocrystal.