Rational Design of Emissive NIR‐Absorbing Chromophores: RhIII Porphyrin‐Aza‐BODIPY Conjugates with Orthogonal Metal–Carbon Bonds |
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| Authors: | Jinfeng Zhou Lizhi Gai Dr Zhikuan Zhou Wu Yang Dr John Mack Kejing Xu Prof Jianzhang Zhao Dr Yue Zhao Dr Hailin Qiu Prof Kin Shing Chan Prof Zhen Shen |
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| Affiliation: | 1. State Key Laboratory of Coordination Chemistry, Collaborative Innovation Center of Advanced Microstructures, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, P. R. China;2. Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, P. R. China;3. Department of Chemistry, Rhodes University, Grahamstown, South Africa;4. State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian, P. R. China |
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| Abstract: | The facile synthesis of Group 9 RhIII porphyrin‐aza‐BODIPY conjugates that are linked through an orthogonal Rh?C(aryl) bond is reported. The conjugates combine the advantages of the near‐IR (NIR) absorption and intense fluorescence of aza‐BODIPY dyes with the long‐lived triplet states of transition metal rhodium porphyrins. Only one emission peak centered at about 720 nm is observed, irrespective of the excitation wavelength, demonstrating that the conjugates act as unique molecules rather than as dyads. The generation of a locally excited (LE) state with intramolecular charge‐transfer (ICT) character has been demonstrated by solvatochromic effects in the photophysical properties, singlet oxygen quantum yields in polar solvents, and by the results of density functional theory (DFT) calculations. In nonpolar solvents, the RhIII conjugates exhibit strong aza‐BODIPY‐centered fluorescence at around 720 nm (ΦF=17–34 %), and negligible singlet oxygen generation. In polar solvents, enhancements of the singlet‐oxygen quantum yield (ΦΔ=19–27 %, λex=690 nm) have been observed. Nanosecond pulsed time‐resolved absorption spectroscopy confirms that relatively long‐lived triplet excited states are formed. The synthetic methodology outlined herein provides a useful strategy for the assembly of functional materials that are highly desirable for a wide range of applications in material science and biomedical fields. |
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| Keywords: | near-IR absorption and fluorescence orthogonal rhodium-carbon bond porphyrinoids rhodium solvatochromism |
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