Iridium-Based High-Sensitivity Oxygen Sensors and Photosensitizers with Ultralong Triplet Lifetimes

The photophysics of a series of bichromophoric molecules featuring an intramolecular triplet energy transfer between a triscyclometalated iridium(III) complex and covalently linked organic group are studied. By systematically varying the energy gap (0.1-0.3 eV) between the donor (metal complex) and acceptor (pyrene unit), reversible triplet energy transfer processes with equilibrium constant K ranging from ca. 500 to 40 000 are established. Unique photophysical consequences of such large K values are observed. Because of the highly imbalanced forward and backward energy transfer rates, triplet excitons dominantly populate the acceptor moiety in the steady state, giving rise to ultralong luminescence lifetimes up to 1-4 ms. Because the triscyclometalated Ir and triplet pyrene groups both impart relatively small nonradiative energy loss, decent phosphorescence quantum yields (Phi = 0.1-0.6) are attained in spite of the exceptionally prolonged excited states. By virtue of such precious combination of long-lived triplet state and high Phi, these bichromophoric molecules can serve as highly sensitive luminescent sensors for detecting trace amount of O-2 and as potent photosensitizers for producing singlet oxygen even under low-oxygen content conditions.

研究了一系列双发色团分子的光物理性质，这些分子具有三（环金属化）铱（III）配合物和共价连接的有机基团之间的分子内三重态能量转移。通过系统地改变供体（金属配合物）和受体（芘单元）之间的能隙（0.1 - 0.3 eV），建立了平衡常数K约为500至40000的可逆三重态能量转移过程。观察到了如此大的K值所带来的独特光物理结果。由于正向和反向能量转移速率高度不平衡，在稳态下三重态激子主要聚集在受体部分，从而产生长达1 - 4毫秒的超长发光寿命。由于三（环金属化）铱和三重态芘基团都具有相对较小的非辐射能量损失，尽管激发态异常延长，但仍获得了可观的磷光量子产率（Φ = 0.1 - 0.6）。凭借长寿命三重态和高Φ的这种宝贵组合，这些双发色团分子可作为高灵敏度的发光传感器用于检测痕量的O₂，并作为有效的光敏剂用于即使在低氧含量条件下产生单线态氧。