Heat trapping in a nano-layered microenvironment: Estimation of temperature by thermal sensing molecules

We have previously found the reversible photo-induced expansion and contraction of the organic/inorganic clay hybrids, and even sliding of niobate nano-sheets at macroscopic level of organic/inorganic niobate hybrids induced by the molecular photoisomerization of polyfluoroalkylated azobenzene derivative (C3F-Azo-C6H) intercalated within the interlayer, which is viewed as an artificial muscle model unit. Based on systematic investigation of steady state photoisomerization and transient behavior of the reaction, we comprehended the phenomena to be caused by a trapping of excess energy liberated during the isomerization as well as the relaxation processes upon excitation of azobenzene chromophores within the interlayer of hybrid. In this paper, quantitative estimation of transient ‘heat’ trapped in various microenvironments has been studied by each co-intercalation of temperature sensing dye molecule – Rhodamine B (RhB) or Tris(bipyridine)ruthenium(II) chloride (Rubpy) with C3F-Azo-C6H within clay (SSA) nano layers. The amounts of dye molecules co-intercalated were made it so trace that it didn’t alter the bi-layered structure of the hybrid. The temperature of the microenvironment surrounding the probe molecules was estimated from the emission lifetime analysis. The evidently reduced emission lifetimes in C3F-Azo-C6H/SSA and C3H-Azo-C6H/SSA hybrids in film state indicated the elevation of temperature of the micro-environment upon excitation of chromophores, which demonstrated our previous hypothesis to rationalize the high reactivity of isomerization in hybrid film state caused by a heat trapping with multi-step dissipation of the excess energy. With the hybrid of hydrocarbon analogue (C3H-Azo-C6H), a distinct difference in temperature gradient was found to show a crucial role of perfluoroalkyl chain of surfactant that dam up the excess energy to retard its dissipation and to lead to three-dimensional morphological motion.