PDF(Pubmed)
Abstract：
Diblock conjugated oligomers are π-conjugated molecules that contain two segments having distinct frontier orbital energies and HOMO-LUMO gap offsets. These oligomers are of fundamental interest to understand how the distinct π-conjugated segments interact and modify their excited state properties. The current paper reports a study of two series of diblock oligomers that contain oligothiophene (Tn) and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT) segments that are coupled by either ethynyl (-C≡C-) or trans-(-C≡C-)2Pt(II)(PBu3)2 acetylide linkers. In these structures, the Tn segment is electron rich (donor), and the TBT is electron poor (acceptor). The diblock oligomers are characterized by steady-state and time-resolved spectroscopy, including UV-visible absorption, fluorescence, fluorescence lifetimes, and ultrafast transient absorption spectroscopy. Studies are compared in several solvents of different polarity and with different excitation wavelengths. The results reveal that the (-C≡C-) linked oligomers feature a delocalized excited state that takes on a charge transfer (CT) character in more polar media. In the (-C≡C-)2Pt(II)(PBu3)2-linked oligomers, there is weak coupling between the Tn and TBT segments. Consequently, short wavelength excitation selectively excites the Tn segment, which then undergoes ultrafast energy transfer (~1 ps) to afford a TBT-localized excited state.
摘要：
二嵌段共轭低聚物是π-共轭分子,其包含具有不同的前沿轨道能量和HOMO-LUMO间隙偏移的两个片段。这些低聚物对理解不同的π-共轭链段如何相互作用和改变它们的激发态性质具有根本的兴趣。本文报道了对两个系列的二嵌段低聚物的研究，这些低聚物包含低聚噻吩（Tn）和4,7-双（2-噻吩基）-2,1,3-苯并噻二唑（TBT）链段，这些链段通过乙炔基（-C=C-）或反式-（-C=C-）2Pt（II）（PBu3）2乙酰基连接剂。在这些结构中,Tn段是富电子(供体)，并且TBT是弱电子的(受体)。二嵌段低聚物通过稳态和时间分辨光谱进行表征，包括紫外可见吸收，荧光，荧光寿命,和超快瞬态吸收光谱。在不同极性和不同激发波长的几种溶剂中进行了比较。结果表明，（-C=C-）连接的低聚物具有离域激发态，在极性更大的介质中具有电荷转移（CT）特征。在（-C=C-）2Pt（II）（PBu3）2连接的低聚物中，Tn和TBT段之间存在弱耦合。因此,短波长激发选择性地激发Tn段，然后进行超快能量转移（〜1ps）以提供TBT局部激发态。
