Raman investigation of local photo‐bleaching in TDBC dye layer for photonics applications

Local photo-bleaching in dye layers is a promising method to pattern organic emitters for photonics applications like strong coupling researches or wavelength selective grating fabrication with tetrachloro diethyl benzimidazolo carbocyanine (TDBC) J-aggregated layers. However, the understanding of the material change with bleaching in such layers is still ambiguous, which limits this method to fully exploit its potential. Raman spectroscopy is a fast, nondestructive, and readily technique to probe a material with micrometer spatial resolution, but the conditions to explore bleached TDBC layers are not well known. In this work, we have investigated active and bleached TDBC layers by Raman spectroscopy at different wavelengths in correlation with their optical properties. For active TDBC, Raman vibrations are well evidenced only in resonant configuration with suitable probe wavelengths (i.e., when layer absorption is high and emission is low). For bleached TDBC, because layer absorption is limited to the ultraviolet (UV) range, Raman peaks are observed only under UV illumination with similar transitions compared with active layer that indicates that TDBC molecules are barely affected by the bleaching mechanism, even if the optical properties are changed around the fundamental transition. Such assumption was confirmed by X-ray photoelectron spectroscopy (XPS) measurements indicating close stoichiometry and limited changes in the N chemical bonds between active and bleached materials. This study allows a better understanding of the local photo-bleaching in TDBC dye layer for photonics applications and highlights the deep UV Raman spectroscopy as relevant tool for studying bleached organic emitters.