Heat trapping with restricted energy dissipation in polyfluorinated supra molecular environment: Wavelength dependency of energy deposition

Following our previous report on the heat trapping in organic/inorganic hybrid compound with bilayer structure formed by cationic polyfluorinated surfactant containing azobenzene moiety (C3F-Azo-C6H) in the interlayer of cation-exchangeable synthetic clay (Smecton SA: SSA) nanosheets having been probed by a temperature sensing Rhodamine B (RhB) upon excitation by a fixed wavelength of visible light, a systematic study of the effect of wavelength dependency for the excitation was carried out to get deeper insight into the heat trapping. Evident wavelength effect of excitation on the temperature elevation was observed. Among three components in the fluorescence lifetime (τ₁, τ₂, τ₃) of RhB, the local temperatures T₁, T₂ deduced from τ₁, τ₂ exhibited a systematic temperature elevation upon excitation of RhB with a shorter wavelength of visible light (570–520 nm). Estimation of the energy stored against the energy input indicated that an excess energy initially deposited at Franck-Condon state is retained in a limited number of local modes during the fluorescence lifetime through a pretty slow intramolecular vibrational relaxation (IVR) in the interlayer. Structural analysis by TD-DFT calculation strongly suggested that all the local modes within RhB are classified into four groups (I–IV), which well coincides with the prediction by a comparison analysis in respect to the energy stored against the energy input to rationalize that the IVR of RhB for τ₁ component (T₁) in the interlayer is limited among the local mode groups I (#1–10)–II (#11–21) and τ₂ component (T₂) being restricted up to group III (# 22–36). The systematic study revealed that the hybrid compound C3F-Azo-C6H/SSA provides a unique microenvironment having gaseous/vacuum-like atmosphere to a molecule incorporated in the narrow gap space sandwiched by neighboring C3F-Azo-C6H molecules in the interlayer to allow an inherently slow IVR.