Physical Chemistry and Applied Spectroscopy, Chemistry Division, Mail Stop J567, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
J Phys Chem B. 2009 Dec 17;113(50):16110-7. doi: 10.1021/jp906645d.
We report reversible thermochromism of a conjugated polymer, poly{2,5-bis[3-(N,N-diethylamino)-1-oxapropyl]-1,4-phenylenevinylene} (DAO-PPV), in diluted solutions of toluene and 1,2-dichlorobenzene. By means of temperature- and solvent-dependent steady-state spectroscopy, picosecond time-resolved photoluminescence spectroscopy, and dynamic light scattering, we provide new insights into the role of polymer aggregates in defining the thermochromic behavior of PPVs. We find DAO-PPV to exhibit a low temperature state with vibronically structured red visible absorption and emission spectra. Structurally, this low temperature state is a densely packed and disordered polymer aggregate, which contains a fraction of well-ordered, packed polymer chains. These ordered regions serve as low energy trap sites for the more disordered regions in the aggregate, thus regulating the final emission of the aggregate and imposing a vibronically resolved emission spectrum, which is usually associated with emission from one or a few chromophores. The high temperature state of DAO-PPV is a loose aggregate, with structureless absorption and emission spectra in the green visible range. Structurally, the loose aggregate is a well-solvated aggregate retaining the physical dimension of the dense aggregate but for which interchain interactions are diminished with the increase of temperature. As a result, the spectroscopic behavior of the loose aggregate is very similar if not identical to that of the single polymer chain. Increased solubility untangles polymer aggregates into single, dispersed, polymer chains, as we demonstrate here for DAO-PPV in 1,2-dichlorobenzene and at high temperature.
我们报告了一种共轭聚合物聚{2,5-双[3-(N,N-二乙基氨基)-1-氧代丙基]-1,4-亚苯基乙烯基}(DAO-PPV)在甲苯和 1,2-二氯苯稀释溶液中的可逆热致变色。通过温度和溶剂依赖的稳态光谱、皮秒时间分辨光致发光光谱和动态光散射，我们提供了新的见解，深入了解聚合物聚集体在定义 PPV 的热致变色行为中的作用。我们发现 DAO-PPV 表现出低温状态，具有振动结构的红色可见吸收和发射光谱。从结构上看，这种低温状态是一种致密无序的聚合物聚集体，其中包含一部分有序排列的聚合物链。这些有序区域作为聚集体中更无序区域的低能陷阱位点，从而调节聚集体的最终发射，并施加一个振动分辨的发射光谱，通常与一个或几个发色团的发射有关。DAO-PPV 的高温状态是一种松散的聚集体，具有无定形的吸收和发射光谱在绿色可见光范围内。从结构上看，松散的聚集体是一种良好溶剂化的聚集体，保留了致密聚集体的物理尺寸，但随着温度的升高，链间相互作用减弱。因此，松散聚集体的光谱行为非常相似，如果不是完全相同的话，也与单个聚合物链的光谱行为非常相似。增加的溶解度将聚合物聚集体解开为单个、分散的聚合物链，正如我们在这里为 DAO-PPV 在 1,2-二氯苯和高温下所证明的那样。
