Sudeep P K, James P V, Thomas K George, Kamat Prashant V
Radiation Laboratory, University of Notre Dame, Indiana 46556, USA.
J Phys Chem A. 2006 May 4;110(17):5642-9. doi: 10.1021/jp0603637.
The rigid rodlike character of phenyleneethynylenes and their ability to communicate charge/excitation energy over long distances have made them useful as molecular linkers in the light energy harvesting assemblies and molecular electronics devices. These linker molecules themselves possess rich photochemistry as evident from the relatively large yields of the excited singlet (0.5-0.66) and triplet (0.4-0.5) states of two model oligomers, 1,4-bis(phenylethynyl)-2,5-bis(hexyloxy)benzene (OPE-1) and 1,4-bis((4-phenylethynyl)phenylethynyl)-2,5-bis(hexyloxy)benzene (OPE-2). In particular, the long-lived triplet excited state is capable of undergoing deactivation by self-quenching processes such as ground-state quenching and triplet-triplet (T-T) annihilation. The T-T annihilation occurs with a nearly diffusion-controlled rate (approximately 2 x 10(9) M(-1) s(-1)), and ground-state quenching occurs with a rate constant of approximately 6 x 10(7) M(-1) s(-1). The electron transfer from the excited OPE-1 and OPE-2 to benzoquinone as characterized from the transient absorption spectroscopy illustrates the ability of these molecules to shuttle the electrons to acceptor moieties. In addition, pulse radiolysis experiments confirm the spectroscopic fingerprint of the cation radical (or "trapped hole") with absorption bands in the 500-600 nm region.
亚苯基乙炔的刚性棒状结构及其在长距离上传递电荷/激发能的能力，使其成为光能收集组件和分子电子器件中有用的分子连接体。这些连接体分子本身具有丰富的光化学性质，从两种模型低聚物1,4-双（苯乙炔基）-2,5-双（己氧基）苯（OPE-1）和1,4-双（（4-苯乙炔基）苯乙炔基）-2,5-双（己氧基）苯（OPE-2）的激发单重态（0.5 - 0.66）和三重态（0.4 - 0.5）的相对较高产率中可见一斑。特别地，长寿命的三重态激发态能够通过诸如基态猝灭和三重态-三重态（T-T）湮灭等自猝灭过程发生失活。T-T湮灭以接近扩散控制的速率（约2×10⁹ M⁻¹ s⁻¹）发生，基态猝灭的速率常数约为6×10⁷ M⁻¹ s⁻¹。从瞬态吸收光谱表征的从激发的OPE-1和OPE-2到苯醌的电子转移，说明了这些分子将电子穿梭到受体部分的能力。此外，脉冲辐解实验证实了阳离子自由基（或“捕获空穴”）在500 - 600 nm区域具有吸收带的光谱特征。
