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      Heavy atom free singlet oxygen generation: doubly substituted configurations dominate S1 states of Bis-BODIPYs

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      Author
      Duman, S.
      Cakmak, Y.
      Kolemen, S.
      Akkaya, E. U.
      Dede, Y.
      Date
      2012
      Source Title
      Journal of Organic Chemistry
      Print ISSN
      0022-3263
      Electronic ISSN
      1520-6904
      Publisher
      American Chemical Society
      Volume
      77
      Issue
      10
      Pages
      4516 - 4527
      Language
      English
      Type
      Article
      Item Usage Stats
      150
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      174
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      Abstract
      S0, S1, and T1 states of various orthogonal 8,8′ and 8,2′-bis-boradiaza-s-indacene (BODIPY) dyes, recently (Angew. Chem., Int. Ed. 2011, 50, 11937) proposed as heavy atom free photosensitizers for O2(1 Δg) generation, were studied by multireference quantum chemical approaches. S0→S1 excitation characteristics of certain bis-BODIPYs are shown to be drastically different than the parent BODIPY chromophore. Whereas a simple HOMO→LUMO-type single substitution perfectly accounts for the BODIPY core, S1 states of certain orthogonal bisBODIPYs are described as linear combinations of doubly substituted (DS) configurations which overall yield four electrons in four singly occupied orbitals. Computed DS character of S1, strongly correlated with facile 1 O2 production, was presumed to occur via S1→T1 intersystem crossing (ISC) of the sensitizer. Further confirmation of this relation was provided by newly synthesized BODIPY derivatives and comparison of spectroscopic properties of their dimers and monomers. Near-IR absorption, desired for potential photodynamic therapy applications, was not pursuable for bis-chromophores by the standard strategy of π-extension, as DS singlet states are destabilized. Decreased exchange coupling in π-extended cases appears to be responsible for this destabilization. Comparisons with iodine incorporated bis-BODIPYs suggest that the dynamics of 1 O2 generation via DS S1 states are qualitatively different from that via ISC originating from heavy atom spin−orbit coupling. Although red-shifting the absorption wavelength to enter the therapeutic window does not seem attainable for orthogonal bisBODIPYs with DS S1 states, modifications in the chromophore cores are shown to be promising in fine-tuning the excitation characteristics.
      Permalink
      http://hdl.handle.net/11693/21472
      Published Version (Please cite this version)
      http://dx.doi.org/10.1021/jo300051v
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      • Department of Chemistry 594
      • Institute of Materials Science and Nanotechnology (UNAM) 1775
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