Photo-switched storage and release of guest molecules in the pore void of coumarin-modified MCM-41

A photoresponsive coumarin derivative was grafted on the pore outlet of Si-MCM-41. Irradiation of UV light longer than 310-nm wavelength to this coumarin-modified MCM-41 induced the photodimerization of coumarin to close the pore outlet with cyclobutane dimer. Guest molecules such as phenanthrene neither can enter nor escape from the one-dimensional, isolated, individual pores of MCM-41. On the other hand, the irradiation to the dimerized-coumarin-modified MCM-41 with shorter wavelength UV light around 250 nm regenerates the coumarin monomer derivative by the photocleavage of cyclobutane dimer, and guest molecules included inside are released from the pore void. For the first time, this intermolecular reversible photodimerization-cleavage cycle realized photo-switched storage and release of guest molecules from coumarin-modified MCM-41. Coumarin-modified MCM-41 prepared using tetradecyltrimethylammonium bromide as surfactant was able to store 21.6 wt % of phenanthrene as guest molecule after photodimerization and washing with n-hexane. Among the four different methods studied for the modification by the coumarin derivative, a grafting procedure with as-synthesized MCM-41 for short reaction time was found to be the most effective for the dense attachment of coumarin-derived monomer at the pore outlets of MCM-41, which is essential for effective storage-release controlled release.