Effective inclusion of chlorophyllous pigments into mesoporous silica modified with α,ω-diols

FSM-type mesoporous silica modified with various diols was utilized as an inorganic medium for immobilizing chlorophyll a (Chl a) without denaturation. The energy transfer from Chl b to Chl a in the mesopores was also observed for the first time. Silanol groups on the mesoporous silica were esterified with diols, and this was confirmed by ¹³C MAS NMR, IR, N₂ adsorption, and elemental analysis. The suppression of the pigment degradation in modified FSM was confirmed by both visible absorption spectroscopy of the FSM/Chl compounds and the analysis of the extracts from FSM/Chl by high-performance liquid chromatography. The fluorescence emission bands of Chl a and Chl b in FSM modified with 1,6-hexanediol appeared at 672 and 654 nm, respectively. In the FSM/Chl containing both Chl a and Chl b, the emission band due to Chl b was decreased whereas the band due to Chl a was increased. This is in sharp contrast to the emission spectrum of an acetone solution containing both of Chls, implying energy transfer from Chl b to Chl a in modified mesoporous silica.