Cyclometalated platinum(II) 6-phenyl-4-(9,9-dihexylfluoren-2-yl)-2,2'-bipyridine complexes: synthesis, photophysics, and nonlinear absorption.
Cyclometalated platinum(II) 6-phenyl-4-(9,9-dihexylfluoren-2-yl)-2,2'-bipyridine complexes: synthesis, photophysics, and nonlinear absorption.
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DOI：
10.1021/ic902281a
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发表时间：
2010-04
影响因子：
4.6
通讯作者：
Pin Shao;Yunjing Li;Jing Yi;T. Pritchett;Wenfang Sun
中科院分区：
文献类型：
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作者：
Pin Shao;Yunjing Li;Jing Yi;T. Pritchett;Wenfang Sun
合成了一系列单核和双核环金属铂(II)6-phenyl-4-(9，9-dihexylfluoren-2-yl)-2，2‘-bipyridine配合物(F-1-F-5)，并系统地研究了它们的光物理性质。所有的配合物在紫外区都有很强的(1)pi，pi*吸收带，在可见光区有一个宽的无结构的电荷转移带。与F-1和F-2相比，F-3-F-5的电荷转移带变宽和红移，这是因为F-3-F-5中存在给电子的乙酰基配体以及配体间电荷转移的参与。双核配合物F-5的摩尔消光系数远高于单核配合物F-1-F-4，表明通过桥联配体的电子耦合作用。当在电荷转移吸收带激发时，配合物在600 nm附近表现出长寿命的红色/橙色发射，这归因于金属-配体/配位内和电荷转移发射((3)MLCT/(3)ILCT)的三重态。对于77K的发射，考虑到发射能量、光谱形状、寿命和热致斯托克斯位移，将发射态暂定为(3)F-2-F-4的MLCT，和(3)F-1和F-5的MLCT/(3)pi，pi*。F-1-F-4在可见光到近红外区表现出宽的三重态瞬时差吸收，其寿命与从(3)MLCT/(3)ILCT发射衰变测得的寿命相当。因此，F-1-F-4对532 nm的纳秒激光脉冲有很强的反饱和吸收。用ns和ps两种激光脉冲在532 nm处进行了Z扫描实验，并用五带模型对实验数据进行了拟合，提取了单态和三态激发态吸收截面。反饱和吸收的程度遵循这样的趋势：F-1=F-2>；F-3>；F-4>；F-5，这主要由三重态激发态吸收截面与基态吸收截面之比和三重态激发态量子产额决定。比较了F-1、F-2和F-3的光物理性质，发现F-1-F-3的低能电荷转移吸收带具有较大的摩尔消光系数，三重态寿命较长，发射量子产率较高，激发态吸收截面与基态吸收截面之比增大。
A series of mononuclear and dinuclear cyclometalated platinum(II) 6-phenyl-4-(9,9-dihexylfluoren-2-yl)-2,2'-bipyridine complexes (F-1-F-5) were synthesized and their photophysical properties were systematically investigated. All complexes exhibit strong (1)pi,pi* absorption bands in the UV region, and a broad, structureless charge transfer band in the visible region. The charge-transfer band is broadened and red-shifted for F-3-F-5 compared to those for F-1 and F-2 because of the electron-donating acetylide ligand and the involvement of the ligand-to-ligand charge transfer character. The molar extinction coefficients for the dinuclear complex F-5 are much higher than those for the mononuclear complexes F-1-F-4, indicating the electronic coupling through the bridge ligand. All complexes are emissive in solution at room temperature and in glassy matrix at 77 K. When excited at the charge transfer absorption band, the complexes exhibit a long-lived red/orange emission around 600 nm, which is attributed to a triplet metal-to-ligand charge transfer/intraligand charge transfer emission ((3)MLCT/(3)ILCT). For emission at 77 K, the emitting state is tentatively assigned as (3)MLCT for F-2-F-4, and (3)MLCT/(3)pi,pi* for F-1 and F-5 taking into account the emission energy, the shape of the spectrum, the lifetime, and the thermally induced Stokes shift. F-1-F-4 exhibit broad triplet transient difference absorption in the visible to the near-IR region, with a lifetime comparable to those measured from the decay of the (3)MLCT/(3)ILCT emission. Therefore, F-1-F-4 give rise to a strong reverse saturable absorption for ns laser pulses at 532 nm. Z-scan experiments were carried out at 532 nm using both ns and ps laser pulses, and the experimental data was fitted by a five-band model to extract the singlet and triplet excited-state absorption cross sections. The degree of reverse saturable absorption follows this trend: F-1 = F-2 > F-3 > F-4 > F-5, which is mainly determined by the ratio of the triplet excited-state absorption cross-section to that of the ground-state and the triplet excited-state quantum yield. Comparison of the photophysics of F-1, F-2, and F-3 to those of their corresponding Pt complexes without the fluorenyl substituent discovers that F-1-F-3 exhibit larger molar extinction coefficients for their low-energy charge transfer absorption band, longer triplet excited-state lifetimes, higher emission quantum yields, and increased ratios of the excited-state absorption cross-section to that of the ground-state.