Ligand-Centred Fluorescence and Electronic Relaxation Cascade at Vibrational Time Scales in Transition-Metal Complexes

详细信息    查看全文

• 作者：Fabrizio Messina ; Enrico Pomarico ; Mahsa Silatani ; Etienne Baranoff ; Majed Chergui
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2015
• 出版时间：November 19, 2015
• 年：2015
• 卷：6
• 期：22
• 页码：4475-4480
• 全文大小：348K
• ISSN：1948-7185

文摘

Using femtosecond-resolved photoluminescence up-conversion, we report the observation of the fluorescence of the high-lying ligand-centered (LC) electronic state upon 266 nm excitation of an iridium complex, Ir(ppy)₃, with a lifetime of 70 卤 10 fs. It is accompanied by a simultaneous emission of all lower-lying electronic states, except the lowest triplet metal-to-ligand charge-transfer (³MLCT) state that shows a rise on the same time scale. Thus, we observe the departure, the intermediate steps, and the arrival of the relaxation cascade spanning 鈭?.6 eV from the ¹LC state to the lowest ³MLCT state, which then yields the long-lived luminescence of the molecule. This represents the first measurement of the total relaxation time over an entire cascade of electronic states in a polyatomic molecule. We find that the relaxation cascade proceeds in 鈮?0 fs, which is faster than some of the highest-frequency modes of the system. We invoke the participation of the latter modes in conical intersections and their overdamping to low-frequency intramolecular modes. On the basis of literature, we also conclude that this behavior is not specific to transition-metal complexes but also applies to organic molecules.