Multiphonon Relaxation in Molecular Lanthanoid Luminescence

由电子态和振动泛音相互作用引起的分子化合物激发态的非辐射失活（多声子弛豫，MR）是发光系统光物理中最基本的现象之一。最有趣的一类发光团是在光谱的近红外区域（约650-2000 nm）发射的分子类镧络合物，它通过非谐波高能振荡器受到MR的严重阻碍。尽管近红外发光在生物医学成像或光学通信等领域具有巨大的技术潜力，但对这些物种中确定MR的复杂性的详细经验和理论理解仍处于起步阶段。目前的建议旨在通过发展对分子镧系发光的MR的全面理解来缓解这种情况。实现这一目标的关键方法是有机合成立体化学定义明确的类镧配合物，这些配合物系统地标记为较重的同位素（例如C-D而不是C-H）。这些量身定制的同位素模型系统可以量化配体中典型结构基序诱导MR的关键参数。特别是，该项目需要确定溶液中的三维复杂结构（顺磁1H NMR），非辐射失活率（时间分辨发光光谱）和各种耦合振荡器片段的振动泛音特性（近红外吸收光谱），然后在已知的非辐射跃迁感应共振机制的理论框架下整合所有经验数据。对高能、非谐振子的磁共振的突破性的、统一的理解将远远超出目前最先进的水平，并补充分子光物理所有领域中众所周知的谐振、低能振子的能隙定律。

Non-radiative deactivation of excited levels in molecular compounds by the interaction of electronic states and vibrational overtones (= multiphonon relaxation, MR) is one of the most fundamental phenomena in the photophysics of light-emitting systems. One of the most interesting class of luminophores that are severely hampered by MR via anharmonic, high-energy oscillators are molecular lanthanoid complexes that emit in the near-infrared region of the spectrum (ca. 650-2000 nm). A detailed empirical and theoretical understanding of the intricacies determining MR in these species is still in its very infancy despite of the great technological potential of near-IR luminescence in areas like biomedical imaging or optical telecommunication. The current proposal aims at alleviating this situation by developing a comprehensive understanding of MR in molecular lanthanoid luminescence. The key enabling methodology for its realization is the organic synthesis of stereochemically well defined lanthanoid complexes which are systematically labeled with heavier isotopes (e.g. C-D instead of C-H). These tailor-made, isotopologic model systems allow the quantification of critical parameters for MR induced by typical structural motifs in the ligands. In particular, the project entails the determinations of the 3D complex structures in solution (paramagnetic 1H NMR), the non-radiative deactivation rates (time-resolved luminescence spectroscopy) and the vibrational overtone properties (near-IR absorption spectroscopy) of various coupled oscillator fragments, followed by integration of all empirical data under the known theoretical framework of the inductive-resonant mechanism of non-radiative transitions. The desired groundbreaking, unified understanding of MR for high-energy, anharmonic oscillators would go far beyond the current state-of-the-art and complement the well-known energy gap law for harmonic, low-energy oscillators in all areas of molecular photophysics.