Laboratory of Photochemistry and Energy Conversion, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, 05508-900, São Paulo, SP, Brazil.
J Phys Chem A. 2010 Nov 25;114(46):12129-37. doi: 10.1021/jp104692w. Epub 2010 Oct 28.
Excited-state dynamics in fac-Re(CO)(3)(Me(4)phen)(cis-L) (Me(4)phen = 3,4,7,8-tetramethyl-1,10-phenanthroline, L = 4-styrylpyridine (stpy) or 1,2-bis(4-pyridyl)ethylene (bpe)) were investigated by steady-state and time-resolved techniques. A complex equilibrium among three closely lying excited states, (3)IL(cis-L), (3)MLCT(Re→Me(4)phen), and (3)IL(Me(4)phen), has been established. Under UV irradiation, cis-to-trans isomerization of coordinated cis-L is observed with a quantum yield of 0.15 in acetonitrile solutions. This photoreaction competes with radiative decay from (3)MLCT(Re→Me(4)phen) and (3)IL(Me(4)phen) excited states, leading to a decrease in the emission quantum yield relative to the nonisomerizable complex fac-Re(CO)(3)(Me(4)phen)(bpa) (bpa = 1,2-bis(4-pyridyl)ethane). From temperature-dependent time-resolved emission measurements in solution and in poly(methyl methacrylate) (PMMA) films, energy barriers (ΔE(a)) for interconversion between (3)MLCT(Re→Me(4)phen) and (3)IL(Me(4)phen) emitting states were determined. For L = cis-stpy, ΔE(a) = 11 (920 cm(-1)) and 15 kJ mol(-1) (1254 cm(-1)) in 5:4 propionitrile/butyronitrile and PMMA, respectively. For L = cis-bpe, ΔE(a) = 13 kJ mol(-1) (1087 cm(-1)) in 5:4 propionitrile/butyronitrile. These energy barriers are sufficient to decrease the rate constant for internal conversion from higher-lying (3)IL(Me(4)phen) state to (3)MLCT(Re→Me(4)phen), k(i) ≅ 10(6) s(-1). The decrease in rate allows for the observation of intraligand phosphorescence, even in fluid medium at room temperature. Our results provide additional insight into the role of energy gap and excited-state dynamics on the photochemical and photophysical properties of Re(I) polypyridyl complexes.
研究了 fac-Re(CO)(3)(Me(4)phen)(cis-L)（Me(4)phen = 3,4,7,8-四甲基-1,10-菲咯啉，L = 4-苯乙烯基吡啶 (stpy) 或 1,2-双(4-吡啶基)乙烯 (bpe)) 的激发态动力学。通过稳态和时间分辨技术建立了三个紧密相邻的激发态 (3)IL(cis-L)、(3)MLCT(Re→Me(4)phen) 和 (3)IL(Me(4)phen) 之间的复杂平衡。在丙酮腈溶液中，观察到配位顺式-L 的顺式-反式异构化，量子产率为 0.15。该光反应与来自 (3)MLCT(Re→Me(4)phen) 和 (3)IL(Me(4)phen) 激发态的辐射衰减竞争，导致发射量子产率相对于非异构化配合物 fac-Re(CO)(3)(Me(4)phen)(bpa)（bpa = 1,2-双(4-吡啶基)乙烷）降低。从溶液和聚甲基丙烯酸甲酯 (PMMA) 薄膜中的温度依赖的时间分辨发射测量中，确定了 (3)MLCT(Re→Me(4)phen) 和 (3)IL(Me(4)phen) 发射态之间的互变异构能垒 (ΔE(a))。对于 L = cis-stpy，在 5:4 丙腈/丁腈和 PMMA 中，ΔE(a)分别为 11（920 cm(-1)) 和 15 kJ mol(-1)(1254 cm(-1))。对于 L = cis-bpe，在 5:4 丙腈/丁腈中，ΔE(a)为 13 kJ mol(-1)(1087 cm(-1))。这些能垒足以降低来自较高 (3)IL(Me(4)phen) 态的内部转换的速率常数 k(i)≅10(6) s(-1)。速率的降低允许观察到配体内磷光，即使在室温下的流体介质中也是如此。我们的结果为 Re(I) 多吡啶配合物的光化学和光物理性质对能隙和激发态动力学的作用提供了更多的见解。
