Schanze Kirk S, Silverman Eric E, Zhao Xiaoming
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA.
J Phys Chem B. 2005 Oct 6;109(39):18451-9. doi: 10.1021/jp052818i.
A series of platinum-acetylide homo- and copolymers was prepared and characterized by using photophysical methods. The polymers feature repeat units of the type [trans-Pt(PBu3)2(-CC-Ar-CC-)], where Ar = 1,4-phenylene (P) or 2,5-thienylene (T). The properties of homopolymers that contain only the 1,4-phenylene or 2,5-thienylene repeat units were compared with those of random copolymers having the structure -[-(Pt(PBu3)2(-CC-T-CC-))x-(Pt(PBu3)2(-CC-P-CC-))(1-x)-)] where x = 0.05, 0.15, and 0.25. Absorption and photoluminescence spectroscopy demonstrates that the singlet and triplet excitations localized on 1,4-phenylene units are higher in energy relative to those localized on the 2,5-thienylene units. The mechanism and dynamics of intrachain triplet energy transfer from 1,4-phenylene to the 2,5-thienylene repeats were explored in the copolymers. Photoluminescence and nanosecond transient absorption spectroscopy indicate that at room temperature P --> T energy transfer is efficient and rapid (k >> 10(8) s(-1)), even in the copolymer that contains only 5% 2,5-thienylene repeat units. At 77 K, steady-state and time-resolved photoluminescence spectroscopy reveals that triplet energy transfer is much less efficient and a fraction of the triplet excitations is "trapped" on the high-energy 1,4-phenylene units. Intrachain energy transfer is believed to occur by two mechanisms, one involving P --> T singlet energy transfer followed by intersystem crossing, whereas the other involves intersystem crossing prior to P --> T triplet energy transfer. The relationship between the observed energy transfer efficiencies and mechanisms in the copolymers is discussed.
制备了一系列铂乙炔均聚物和共聚物，并采用光物理方法对其进行了表征。这些聚合物的特征重复单元为[trans-Pt(PBu3)2(-CC-Ar-CC-)]类型，其中Ar = 1,4-亚苯基（P）或2,5-噻吩亚基（T）。将仅含有1,4-亚苯基或2,5-噻吩亚基重复单元的均聚物的性质与具有结构-[-(Pt(PBu3)2(-CC-T-CC-))x-(Pt(PBu3)2(-CC-P-CC-))(1-x)-]（其中x = 0.05、0.15和0.25）的无规共聚物的性质进行了比较。吸收光谱和光致发光光谱表明，相对于2,5-噻吩亚基单元上的单重态和三重态激发，1,4-亚苯基单元上的单重态和三重态激发能量更高。在共聚物中探索了链内三重态能量从1,4-亚苯基转移到2,5-噻吩亚基重复单元的机制和动力学。光致发光和纳秒瞬态吸收光谱表明，在室温下，即使在仅含有5% 2,5-噻吩亚基重复单元的共聚物中，P→T能量转移也是高效且快速的（k >> 10(8) s(-1)）。在77 K时，稳态和时间分辨光致发光光谱表明，三重态能量转移效率要低得多，并且一部分三重态激发被“捕获”在高能1,4-亚苯基单元上。链内能量转移被认为通过两种机制发生，一种机制涉及P→T单重态能量转移，随后是系间窜越，而另一种机制涉及在P→T三重态能量转移之前的系间窜越。讨论了共聚物中观察到的能量转移效率与机制之间的关系。
