Treatment of the laser borane anti-B18H22 (compound 1) with iodine in ethanol gives the monoiodinated derivative 7-I-anti-B18H21 (compound 2) in 67% yield, or, by reaction with iodine or ICl in the presence of AlCl3 in dichloromethane, the diiodinated derivative 4,4'-I2-anti-B18H20 (compound 3) in 85% yield. On excitation with 360 nm light, both compounds 2 and 3 give strong green phosphorescent emissions (λmax = 525 nm, ΦL = 0.41 and λmax = 545 nm, ΦL = 0.71 respectively) that are quenched by dioxygen to produce O2(1Δg) singlet oxygen with quantum yields of ΦΔ = 0.52 and 0.36 respectively. Similarly strong emissions can be stimulated via the nonlinear process of two-photon absorption when exciting with 720 or 800 nm light. The high quantum yields of singlet-oxygen production, coupled with the option of two-photon excitation, make compounds 2 and 3 promising O2(1Δg) photosensitizers. The molecular structures of compounds 2 and 3 were determined by single-crystal X-ray crystallographic studies as well as multinuclear NMR spectroscopy and mass spectrometry. Time-resolved UV-vis spectroscopy was used to delineate their photophysical properties, and the electronic-structure properties of the emitting species were determined by means of multiconfigurational quantum-chemistry computations.

Department of Inorganic Chemistry Charles University Prague Hlavova 2030 8 128 43 Prague 2 Czech Republic

Department of Physical Theoretical and Computational Chemistry Mlynská dolina Comenius University Ilkovičova 6 842 15 Bratislava Slovakia

Institute of Inorganic Chemistry of the Czech Academy of Sciences 250 68 Husinec Řež Czech Republic

Instituto de Ciencia Molecular Universitat de València P O Box 22085 ES 46071 València Spain

International Laser Centre Ilkovicova 3 84104 Bratislava Slovak Republic

J Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences Dolejškova 3 182 23 Praha 8 Czech Republic

Université de Lorraine CNRS LPCT F 54000 Nancy France

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