Using the steady-state and time-resolved fluorescence spectroscopy, the behavior of "hairy-rod" oligo- and poly[2,5-bis(hexadecyloxy)-1,4-phenylene]s in tetrahydrofuran solutions was investigated. The materials were prepared by the Yamamoto coupling reaction using zinc as a reducing metal, the nickel(II)/triphenylphosphine complex as a catalyst, and 2,2'-bipyridine as a coligand. The appropriate oligomer fractions were separated by fractional precipitation and characterized by GPC and end group analysis. The fluorescence quantum yield of oligomers and polymers increased with their increasing conjugation length. The fluorescence emission spectra of polymers and longer oligomers exhibited one emission maximum at 390 nm with a single-exponential decay and fluorescence lifetimes (τ) around 1 ns. The substitution in positions 2 and 5 forces the adjacent backbone benzene units out of the plane, which results in twist angles 60-80°, and the bulky substituents exclude the cofacial sandwich-type configuration necessary for excimer formation. However, with shorter oligomers, another emission band at 460 nm appeared. Fluorescence decays at 460 nm were found to be double-exponential with longer excited-state lifetimes [e.g. τ1 = 6.9 ns (76%), τ2 = 2.4 ns (24%)]. With shorter oligomers (dimer, trimer), we assume a sandwich-type configuration with sufficiently close interchain distance and hence the excimer can form. Hydrophobic interactions of long aliphatic side chains in a polar medium play an important role in the excimer formation.
使用稳态和时间分辨荧光光谱技术,研究了“毛状杆”寡聚物和聚[2,5-双(十六烷氧基)-1,4-苯基]在四氢呋喃溶液中的行为。该材料是通过使用锌作为还原金属,镍(II)/三苯基膦配合物作为催化剂,2,2'-联吡啶作为共配体的山本偶联反应制备的。适当的寡聚物分数通过分级沉淀法分离并通过GPC和末端基分析进行表征。随着共轭长度的增加,寡聚体和聚合物的荧光量子产率增加。聚合物和较长的寡聚体的荧光发射光谱在390 nm处显示一个发射峰,具有单指数衰减和荧光寿命(τ)约为1 ns。2和5位置的取代使相邻的骨架苯基单元脱离平面,导致扭曲角度在60-80°之间,而笨重的取代基排斥了必要的共面夹层型构造以形成激聚物。然而,对于较短的寡聚体,另一个发射带在460 nm处出现。在460 nm处的荧光衰减被发现是双指数的,具有较长的激发态寿命[例如τ1=6.9 ns(76%),τ2=2.4 ns(24%)]。对于较短的寡聚体(二聚体、三聚体),我们假设存在足够接近的链间距离的夹层型构造,因此可以形成激聚物。疏水性较长的脂肪侧链在极性介质中的相互作用在激聚物的形成中起重要作用。