The State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China.
J Phys Chem A. 2012 Aug 30;116(34):8693-705. doi: 10.1021/jp305407s. Epub 2012 Aug 21.
In order to better understand the nature of intramolecular charge and energy transfer in multibranched molecules, we have synthesized and studied the photophysical properties of a monomer quadrupolar chromophore with donor-acceptor-donor (D-A-D) electronic push-pull structure, together with its V-shaped dimer and star-shaped trimers. The comparison of steady-state absorption spectra and fluorescence excitation anisotropy spectra of these chromophores show evidence of weak interaction (such as charge and energy transfer) among the branches. Moreover, similar fluorescence and solvation behavior of monomer and branched chromophores (dimer and trimer) implies that the interaction among the branches is not strong enough to make a significant distinction between these molecules, due to the weak interaction and intrinsic structural disorder in branched molecules. Furthermore, the interaction between the branches can be enhanced by inserting π bridge spacers (-C═C- or -C≡C-) between the core donor and the acceptor. This improvement leads to a remarkable enhancement of two-photon cross-sections, indicating that the interbranch interaction results in the amplification of transition dipole moments between ground states and excited states. The interpretations of the observed photophysical properties are further supported by theoretical investigation, which reveal that the changes of the transition dipole moments of the branched quadrupolar chromophores play a critical role in observed the two-photon absorption (2PA) cross-section for an intramolecular charge transfer (ICT) state interaction in the multibranched quadrupolar chromophores.
为了更好地理解多分支分子中分子内电荷和能量转移的性质，我们合成并研究了具有给体-受体-给体（D-A-D）电子推拉结构的单体四极色团的光物理性质，以及其 V 型二聚体和星形三聚体。这些色团的稳态吸收光谱和荧光激发各向异性光谱的比较表明存在弱相互作用（如电荷和能量转移）。此外，单体和支化色团（二聚体和三聚体）的荧光和溶剂化行为相似，这意味着由于支化分子中的弱相互作用和固有结构无序，支化分子之间的相互作用不足以使其之间产生明显的区别。此外，通过在核供体和受体之间插入π桥间隔基（-C═C-或-C≡C-），可以增强支化分子之间的相互作用。这种改进导致双光子截面显著增强，表明支化分子之间的相互作用导致基态和激发态之间的跃迁偶极矩放大。观察到的光物理性质的解释得到了理论研究的进一步支持，这表明支化四极色团的跃迁偶极矩的变化在观察多支化四极色团中分子内电荷转移（ICT）态相互作用的双光子吸收（2PA）截面中起着关键作用。
