title: Photosensitizer that selectively generates singlet oxygen in nonpolar environments: photophysical mechanism and efficiency for a covalent BODIPY dimer.
abstract: Photosensitizers that selectively generate singlet oxygen in non polar/polar microenvironments are highly desirable for photodynamic therapy of tumor but not yet reported. BODIPY (boron-dipyrromethene complexes) covalent dimer 1 is such a photosensitizer that forms singlet oxygen only in hexane, cyclohexane, and toluene significantly but not in polar solvents. Its corresponding monomer is not photoactive in any solvents for forming singlet oxygen. To reveal the mechanism, we measured the excited triplet-, singlet-, and ground-state properties as well as singlet oxygen generation capability with laser flash photolysis, fluorescence spectroscopy, time-correlated single photon counting, and absorption spectroscopy in various solvents. The striking difference is due to the fact that the excited dimer (excimer) undergoes very fast intramolecular charge transfer (ICT) that makes intersystem crossing noncompetitive in polar solvents, while ICT is negligible in nonpolar solvents.
authors.affiliation: Chemistry Department & Center of Instrumental Analysis, Hebei Normal University of Science and Technology, Qinhuangdao, Hebei Province, 066004 China. zhangxianfu@tsinghua.org.cn
authors.forename: Xian-Fu
authors.initials: XF
authors.lastname: Zhang
authors.forename: Xudong
authors.initials: X
authors.lastname: Yang
mesh_terms: D001896:Boron Compounds / Q000737:chemistry*; D003510:Cyclohexanes / Q000737:chemistry; D019281:Dimerization; D006586:Hexanes / Q000737:chemistry; D017319:Photosensitizing Agents / Q000737:chemistry*; D011789:Quantum Theory; D026082:Singlet Oxygen / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D014050:Toluene / Q000737:chemistry
chemical_list: C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D003510:Cyclohexanes; D006586:Hexanes; D017319:Photosensitizing Agents; D012997:Solvents; D026082:Singlet Oxygen; C026385:n-hexane; D014050:Toluene; C506365:Cyclohexane