Department of Chemistry and Molecular Biology, North Dakota State University, Fargo, ND 58108-6050, USA.
Dalton Trans. 2010 Jul 7;39(25):5885-98. doi: 10.1039/b923203f. Epub 2010 May 27.
A systematic photophysical study, i.e. electronic absorption and emission study, on platinum(II) 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine complexes with different alkyl chains and different anions were performed in solutions and in Langmuir-Blodgett (LB) films. Electronic absorption in solution shows high-energy bands that are assigned to pi,pi* transitions within the ligand and a moderately intense metal-to-ligand charge transfer ((1)MLCT) band above 400 nm. All the complexes are emissive at room temperature and at 77 K. When low-polarity solvent, such as hexane was added to the CHCl(3) solutions of these complexes, solvent-induced aggregation occurred, which was evident by the appearance of a broad metal-metal-to-ligand charge transfer ((1)MMLCT) band between 500 and 600 nm in their UV-vis spectra and a new emission band appearing around 670 nm, which is attributed to the (3)MMLCT state. The degree of aggregation is affected drastically by the nature of the counter anion, with complexes 5b, 5c and 5d that contain PF(6)(-), ClO(4)(-) and BF(4)(-) anion, respectively, appearing to more readily aggregate. In contrast, the length of the alkyl chain shows a negligible effect on the degree of aggregation. The emission lifetime measurements further confirm the formation of aggregates. These complexes exhibited selective vapochromic response when exposed to volatile organic compounds (VOCs). Both the alkyl chain length and the counter anion affect the vapochromic effect. Moreover, LB films were fabricated using these amphiphilic platinum complexes and most of the films displayed (3)MMLCT emission. The emission energy and the lifetime in LB films are influenced significantly by the counter anions. Complex 5f mainly emits from a ligand-ligand pi-pi interacted excited state, and 5a-5e exhibit a (3)MMLCT emission. Although no simple systematic correlation could be made between the nature of the counter ion and the electronic absorption and/or emission properties of these platinum complexes in solution and in LB films, we believe that the salient counter ion effects are most likely related to the size and shape of the counter ions.
我们对具有不同烷基链和不同阴离子的铂（II）2,6-双（N-烷基苯并咪唑-2'-基）吡啶配合物进行了系统的光物理研究，即电子吸收和发射研究，在溶液和 Langmuir-Blodgett（LB）薄膜中进行。溶液中的电子吸收显示高能带，这些能带归因于配体内部的π，π*跃迁和 400nm 以上的中等强度金属-配体电荷转移（1MLCT）带。所有配合物在室温下和 77K 时都具有发光性。当将这些配合物的低极性溶剂（例如己烷）添加到 CHCl3 溶液中时，会发生溶剂诱导的聚集，这可以通过在其紫外可见光谱中出现 500nm 至 600nm 之间的宽金属-金属-配体电荷转移（1MMLCT）带以及在 670nm 左右出现新的发射带来证明，这归因于（3）MMLCT 态。聚集度受抗衡阴离子的性质的强烈影响，分别包含 PF6-，ClO4-和 BF4-阴离子的配合物 5b、5c 和 5d 似乎更容易聚集。相比之下，烷基链的长度对聚集度的影响可以忽略不计。发射寿命测量进一步证实了聚集物的形成。这些配合物在暴露于挥发性有机化合物（VOC）时表现出选择性的蒸气致变色响应。烷基链长度和抗衡阴离子都影响蒸气致变色效应。此外，使用这些两亲性铂配合物制备了 LB 薄膜，并且大多数薄膜显示出（3）MMLCT 发射。LB 薄膜中的发射能量和寿命受抗衡阴离子的影响很大。配合物 5f 主要从配体-配体π-π相互作用激发态发射，而 5a-5e 则表现出（3）MMLCT 发射。尽管无法在溶液和 LB 薄膜中这些铂配合物的抗衡离子的性质与电子吸收和/或发射性质之间建立简单的系统相关性，但我们认为明显的抗衡离子效应可能与抗衡离子的大小和形状有关。
