Garakyaraghi Sofia, Crapps Peter D, McCusker Catherine E, Castellano Felix N
Department of Chemistry, North Carolina State University , Raleigh, North Carolina 27695-8204, United States.
Inorg Chem. 2016 Oct 17;55(20):10628-10636. doi: 10.1021/acs.inorgchem.6b01880. Epub 2016 Sep 28.
In the interest of expanding the inventory of available long lifetime, photochemically robust, and strongly reducing Cu(I) MLCT sensitizers, we present detailed structural, photophysical, and electrochemical characterization of [Cu(dipp)], dipp = 2,9-diisopropyl-1,10-phenanthroline, and its sterically encumbered tetramethyl analogue [Cu(diptmp)], diptmp = 2,9-diisopropyl-3,4,7,8-tetramethyl-1,10-phenanthroline. The achiral isopropyl substituents enable similar steric bulk effects to the previously investigated sec-butyl substituents while eliminating the complex NMR structural analyses associated with the presence of two chiral centers in the latter. The photophysical properties of [Cu(diptmp)] are impressive, possessing a 2.3 μs lifetime in deaerated CHCl and a photoluminescence quantum yield of 4.7%, which were slightly attenuated in coordinating tetrahydrofuran (THF) solutions. Nanosecond transient absorption spectroscopy results matched the transient photoluminescence kinetics enabling complete characterization of MLCT excited-state decay in these molecules. The calculated excited-state potential for the Cu/Cu* couple (E = -1.74 V vs Fc) indicated that [Cu(diptmp)]* is a strong photoreductant potentially useful for myriad applications. Ultrafast transient absorption measurements performed in THF solutions are also reported, yielding the relative time scales for both the pseudo-Jahn-Teller distortion (0.4-0.8 ps in [Cu(dipp)] and 0.12-0.5 ps in [Cu(diptmp)]) and singlet-triplet intersystem crossing (6.4-10.1 ps for [Cu(dipp)] and 3.5-5.4 ps for [Cu(diptmp)]) within these molecules. The disparity in the time scales of pseudo-Jahn-Teller distortion and intersystem crossing between two complexes with different anticipated excited-state geometries suggests that strongly impeded structural distortion in the MLCT excited state (i.e., [Cu(diptmp)]) enables more rapid surface crossings in the initial deactivation dynamics.
为了增加长寿命、光化学稳定且强还原的Cu(I) MLCT敏化剂的种类，我们详细介绍了[Cu(dipp)]（dipp = 2,9 - 二异丙基 - 1,10 - 菲咯啉）及其空间位阻四甲基类似物[Cu(diptmp)]（diptmp = 2,9 - 二异丙基 - 3,4,7,8 - 四甲基 - 1,10 - 菲咯啉）的结构、光物理和电化学特性。非手性的异丙基取代基能产生与先前研究的仲丁基取代基类似的空间位阻效应，同时避免了因后者存在两个手性中心而带来的复杂核磁共振结构分析。[Cu(diptmp)]的光物理性质令人印象深刻，在脱气的CHCl中寿命为2.3 μs，光致发光量子产率为4.7%，在配位的四氢呋喃（THF）溶液中略有衰减。纳秒瞬态吸收光谱结果与瞬态光致发光动力学相匹配，从而能够完整地表征这些分子中MLCT激发态的衰变。计算得出的Cu/Cu*电对的激发态势（相对于Fc，E = -1.74 V）表明，[Cu(diptmp)]*是一种强光还原剂，可能在众多应用中有用。还报道了在THF溶液中进行的超快瞬态吸收测量结果，得出了这些分子中伪 Jahn - Teller 畸变（[Cu(dipp)]中为0.4 - 0.8 ps，[Cu(diptmp)]中为0.12 - 0.5 ps）和单重态 - 三重态系间窜越（[Cu(dipp)]为6.4 - 10.1 ps，[Cu(diptmp)]为3.5 - 5.4 ps）的相对时间尺度。具有不同预期激发态几何结构的两种配合物在伪 Jahn - Teller 畸变和系间窜越时间尺度上的差异表明，MLCT激发态（即[Cu(diptmp)]）中强烈受阻的结构畸变使得初始失活动力学中的表面窜越更快。
