Synthesis and Photophysical Characterization of Stable Indium Bacteriochlorins

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• 作者：Michael Krayer ; Eunkyung Yang ; Han-Je Kim ; Hooi Ling Kee ; Richard M. Deans ; Camille E. Sluder ; James R. Diers ; Christine Kirmaier ; David F. Bocian ; Dewey Holten ; Jonathan S. Lindsey
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：May 16, 2011
• 年：2011
• 卷：50
• 期：10
• 页码：4607-4618
• 全文大小：1173K
• 年卷期：v.50,no.10(May 16, 2011)
• ISSN：1520-510X

文摘

Bacteriochlorins have wide potential in photochemistry because of their strong absorption of near-infrared light, yet metallobacteriochlorins traditionally have been accessed with difficulty. Established acid-catalysis conditions [BF₃路OEt₂ in CH₃CN or TMSOTf/2,6-di-tert-butylpyridine in CH₂Cl₂] for the self-condensation of dihydrodipyrrin-acetals (bearing a geminal dimethyl group in the pyrroline ring) afford stable free base bacteriochlorins. Here, InBr₃ in CH₃CN at room temperature was found to give directly the corresponding indium bacteriochlorin. Application of the new acid catalysis conditions has afforded four indium bacteriochlorins bearing aryl, alkyl/ester, or no substituents at the 尾-pyrrolic positions. The indium bacteriochlorins exhibit (i) a long-wavelength absorption band in the 741鈭?82 nm range, which is shifted bathochromically by 22鈭?2 nm versus the analogous free base species, (ii) fluorescence quantum yields (0.011鈭?.026) and average singlet lifetime (270 ps) diminished by an order of magnitude versus that (0.13鈭?.25; 4.0 ns) for the free base analogues, and (iii) higher average yield (0.9 versus 0.5) yet shorter average lifetime (30 vs 105 渭s) of the lowest triplet excited state compared to the free base compounds. The differences in the excited-state properties of the indium chelates versus free base bacteriochlorins derive primarily from a 30-fold greater rate constant for S₁ 鈫?T₁ intersystem crossing, which stems from the heavy-atom effect on spin鈭抩rbit coupling. The trends in optical properties of the indium bacteriochlorins versus free base analogues, and the effects of 5-OMe versus 5-H substituents, correlate well with frontier molecular-orbital energies and energy gaps derived from density functional theory calculations. Collectively the synthesis, photophysical properties, and electronic characteristics of the indium bacteriochlorins and free base analogues reported herein should aid in the further design of such chromophores for diverse applications.