Characteristics of photoluminescence from ruthenium polypyridyl complexes incorporated into silk

Abstract

Characteristics of photoluminescence from polypyridine Ru complexes incorporated into Bombyx mori silk fibroins with several structures have been investigated. The structures of the silk were α-helix, silk I, and silk II, that involve only intra-, both intra- and inter-, and only inter-molecular hydrogen bonds, respectively. Microenvironment in the silk was studied using photoluminescence probe. Maximum wave number of probes in silk was shifted to higher energy than that in water. The wave number decreased in the order, α-helix>silk I>silk II, suggesting that the polarity of the microenvironment is in the order, α-helix<silk I<silk II. The emission lifetime from the MLCT excited state in silk is three times as long as that in water, indicating that the probes exist in rigid microenvironment. There are two kinds of microenvironment around the incorporated probe because of the biexponential decay of the emission. The MLCT excited state lifetime was measured at various temperatures, and thermodynamic parameters such as the sum of radiative and nonradiative rate constants, and the activation energy from MLCT to d–d state were estimated to discuss the characteristics of the silk structures.