Photophysics in solution and Langmuir-Blodgett film and vapochromic behavior of the Pt(II) 2,6-bis(N-alkylbenzimidazol-2′-yl)pyridine complexes with different alkyl chains and counter anions
Photophysics in solution and Langmuir-Blodgett film and vapochromic behavior of the Pt(II) 2,6-bis(N-alkylbenzimidazol-2′-yl)pyridine complexes with different alkyl chains and counter anions
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DOI：
10.1039/b923203f
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发表时间：
2010-01-01
影响因子：
4
通讯作者：
Sun, Wenfang
中科院分区：
文献类型：
--
作者：
Mathew, Iswarya;Sun, Wenfang
对不同烷基链和不同阴离子的2，6-双（N-烷基苯并咪唑-2 '-基）吡啶铂配合物在溶液和LB膜中的电子吸收和发射进行了系统的电子物理研究。溶液中的电子吸收显示出被分配给配体内的pi、pi* 跃迁的高能带和高于400 nm的中等强度的金属-配体电荷转移（（1）MLCT）带。所有配合物在室温和77 K下都有发射。当低极性溶剂（如己烷）加入到这些配合物的CHCl（3）溶液中时，溶剂诱导的聚集发生，这通过在它们的紫外-可见光谱中在500和600 nm之间出现宽的金属-金属-配体电荷转移（（1）MMLCT）带和在670 nm附近出现新的发射带来证明，这归因于（3）MMLCT状态。聚集程度受抗衡阴离子性质的显著影响，分别含有PF（6）（-）、ClO（4）（-）和BF（4）（-）阴离子的络合物5 b、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体的形成。这些配合物表现出选择性的挥发性有机化合物（VOCs）时，暴露于vapochromic响应。烷基链长和抗衡阴离子都影响汽色效应。此外，使用这些两亲性铂络合物制备LB膜，并且大多数膜显示（3）MMLCT发射。平衡阴离子对LB膜的发射能量和寿命有很大的影响。配合物5 f主要从配体-配体π-π相互作用的激发态发射，5a-5e表现出（3）MMLCT发射。虽然没有简单的系统之间的相关性可以作出的反离子的性质和电子吸收和/或这些铂络合物在溶液中和LB膜的发射性能，我们认为，显着的反离子效应最有可能与反离子的大小和形状。
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.