Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy.
Inorg Chem. 2012 Mar 5;51(5):2832-40. doi: 10.1021/ic201903g. Epub 2012 Feb 22.
The synthesis, characterization, photophysics, and time-dependent density functional theory (TD-DFT) calculations of spirobifluorene-bipyridine based iridium(III), osmium(II), and mixed Ir/Os complexes are presented. The preparation of the reference and mixed complexes proceeded step-by-step and microwave irradiation facilitated the complexation of osmium. The absorption of the target heterobimetallic derivative, Ir-L-Os, is described by linear combination of half of the absorption spectra of the homobimetallic analogues, Ir-L-Ir and Os-L-Os, due to the occurrence of mixed ligand and metal based transitions when the spirobifluorene-(bpy)(2) bridging ligand L is linked to the metal, confirming a negligible interaction between the substituted metallic chromophores. TD-DFT calculations on monometallic, homo- and hetero-bimetallic complexes fully disentangled the origin of the absorption features. Noticeably, in the mixed Ir-L-Os complex an almost quantitative energy transfer from the (3)Ir to the (3)Os MLCT state is occurring, with a rate constant of 4.1 × 10(8) s(-1) and nearly exclusively via a Dexter-type mechanism mediated by the orbitals of the spiroconjugated ligand. This result, together with the outcomes of the TD-DFT calculations, supports the existence of spiroconjugation and evidences the interesting role of this kind of bridge in the energy transfer dynamics of the arrays. In all the complexes, moreover, the ligand fluorescence is heavily quenched by energy transfer processes toward the metallic appended units; the rate constant is estimated in the order of 10(10) s(-1) for Ir-L-Os and higher than 10(12) s(-1) for the other complexes. In the heterometallic array, both at room temperature and at 77 K, all photons are thus funneled to the emissive Os (3)MLCT state, which acts as energy trap for the antenna cascade.
呈现了基于螺二芴-联吡啶的铱（III）、锇（II）和混合 Ir/Os 配合物的合成、表征、光物理和含时密度泛函理论（TD-DFT）计算。参考和混合配合物的制备是逐步进行的，微波辐射促进了锇的配合。目标杂双金属衍生物 Ir-L-Os 的吸收由同双金属类似物 Ir-L-Ir 和 Os-L-Os 的吸收光谱的一半线性组合描述，这是由于当螺二芴-（bpy）（2）桥联配体 L 连接到金属时发生混合配体和金属基跃迁，这证实了取代金属发色团之间几乎没有相互作用。对单核、同核和杂核配合物的 TD-DFT 计算完全阐明了吸收特征的起源。值得注意的是，在混合 Ir-L-Os 配合物中，（3）Ir 到（3）Os MLCT 态的能量转移几乎是定量的，速率常数为 4.1×10（8）s（-1），并且几乎完全通过由螺共轭配体的轨道介导的 Dexter 型机制进行。这一结果与 TD-DFT 计算的结果一起，支持了螺共轭的存在，并证明了这种桥在阵列能量转移动力学中的有趣作用。此外，在所有配合物中，配体荧光都被强烈猝灭，这是由于能量转移过程朝向金属附加单元进行；对于 Ir-L-Os，速率常数估计在 10（10）s（-1）的顺序，对于其他配合物则高于 10（12）s（-1）。在杂金属阵列中，无论是在室温还是在 77 K，所有光子都被引导到发射性的 Os（3）MLCT 态，它作为天线级联的能量陷阱。
