Excited-State Properties of Heteroleptic Iridium(III) Complexes Bearing Aromatic Hydrocarbons with Extended Cores

The synthesis, complete structural characterization, electrochemistry, and excited-state dynamics of a series of four bis-heteroleptic iridium(III) charge-transfer complexes composed of a single acac-functionalized and two ortho-metalated 2-phenylpyridine ligands. The formed iodophenyl complex (2) was used as a metallosynthon to introduce extended-core ethynyltolyl (3), ethynylpyrene (4), and ethynylperylene (5) residues into these structures projecting from the acac ancillary ligand. Static and dynamic photoluminescence along with ultrafast and conventional transient absorption measurements in conjunction with cyclic voltammetry were employed to elucidate the nature of the intramolecular energy-transfer processes occurring in the excited states of polychromophores 4 and 5 and are directly compared with those of model complexes 2 and 3. Upon charge-transfer excitation of these molecules, the long-lived triplet-state metal-to-ligand charge-transfer (3MLCT)-based photoluminescence readily observed in 2 and 3 (τ = 1 μs) is nearly quantitatively quenched, resulting from production of the associated triplet intraligand (3IL) excited states in 4 and 5 through intramolecular triplet–triplet energy transfer. The respective formation of the extended-core 3*pyrenyl and 3*perylenyl-localized excited states in 4 and 5 is confirmed by their ultrafast excited-state evolution, which ultimately generates features associated with these 3IL excited states and their greatly extended excited-state lifetimes with respect to the parent complexes 2 and 3.本研究合成了一系列共4种双杂配体铱(III)电荷转移配合物，该类配合物由1个乙酰丙酮（acac）修饰的配体与2个邻环金属化2-苯基吡啶配体构成，并完成了完整的结构表征、电化学测试以及激发态动力学研究。所制备的碘苯基配合物（2）被用作金属合成子，以将延伸核乙炔基甲苯基（3）、乙炔基芘（4）以及乙炔基苝（5）残基引入上述结构中，这些残基由乙酰丙酮辅助配体向外延伸。本研究通过静态与动态光致发光测试、超快及常规瞬态吸收光谱结合循环伏安法，阐明了多发色团配合物4和5激发态下发生的分子内能量转移过程本质，并将其与模型配合物2和3的相关过程进行了直接对比。对这类分子进行电荷转移激发后，在配合物2和3中易于观测到的长寿命三重态金属到配体电荷转移（3MLCT）型光致发光（寿命τ=1 μs）几乎被完全淬灭，这是由于配合物4和5通过分子内三重态-三重态能量转移生成了对应的三重态配体内（3IL）激发态。配合物4和5中分别形成的延伸核3*芘基与3*苝基局域激发态，可通过其超快激发态演化过程得到证实，该过程最终生成了与上述3IL激发态相关的特征信号，且相较于母体配合物2和3，其激发态寿命大幅延长。