Photodimerized 7-hydroxycoumarin with improved solubility in PMMA: Single-photon and two-photon-induced photocleavage in solution and PMMA films

tert-Butyldimethylsilyl-chloride (TBS) revealed to be a photostable protecting group for the photodimerization of 7-hydroxycoumarin in a [2 + 2]-cycloaddition. TBS-functionalized coumarin dimers show an about 100-fold increased solubility in organic solvents enabling them to be easily incorporated into polymeric films, e.g., PMMA. In the described photochemical dimerization reaction almost pure anti-head-to-head isomer is obtained. The single- and two-photon absorption-induced cycloreversion reactions in acetonitrile as well as in PMMA matrix were investigated and the two-photon absorption cross sections and quantum yields were determined to be around 1 GM and about 0.36, respectively. The only product obtained upon photocleavage of the dimer is the TBS-protected 7-hydroxycoumarin monomer. The TBS-protecting group withstands the high light intensities required for two-photon absorption-induced photocleavage without any noticeable degradation. The mild deprotection conditions for tert-butyldimethylsilyl-ethers (TBS-ethers), the chemical stability of the compound as well as its significantly improved solubility in organic solvents and its miscibility with acrylic polymers, make this a very useful compound for potential applications in 3D volumetric optical data storage and photocontrolled drug delivery.