Intrachain photoluminescence properties of conjugated polymers as revealed by long oligothiophenes and polythiophenes diluted in an inactive solid matrix
Intrachain photoluminescence properties of conjugated polymers as revealed by long oligothiophenes and polythiophenes diluted in an inactive solid matrix
复制标题
DOI：
10.1103/physrevb.73.235203
复制
发表时间：
2006-06-01
影响因子：
3.7
通讯作者：
Otsubo, Tetsuo
中科院分区：
文献类型：
--
作者：
Kanemoto, Katsuichi;Sudo, Tatsuji;Otsubo, Tetsuo
研究了固态共轭聚合物的本征链内光致发光动力学。我们重点研究了长β取代低聚硫吩类化合物(8-聚体、12-聚体和16-聚体)和区域规则(RR)和区域随机聚(3-辛基噻吩基)(P3OTS)在非活性固体基质聚丙烯(PP)中的发光性质。低聚硫吩类化合物在4K有良好的0-0荧光光谱和吸收峰，并与环数倒数呈良好的线性关系。光致发光光谱的Franck-Condon分析表明，随着齐聚物链长的增加，以黄里斯因子为代表的电子-声子耦合强度变弱。相反，在RR P3OT中证实了更强的电子-声子耦合的存在，尽管它的链长比低聚物长得多。这可能是由于其立体规则的链构象所致。本工作中使用的材料在PP中稀释后呈现单指数发光衰减，寿命随着链长的增加而减少。除了RR P3OT的情况外，时间分辨光致发光测量表明，除了RR P3OT的情况外，链内激子迁移的存在。由链内迁移引起的能量转移比由链间迁移引起的能量转移小得多。我们的结论是，在噻吩衍生物的吸收转变后的50ps内，噻吩环键周围的扭转角度发生了变化，并且这种扭转变化引起了恒定的斯托克斯位移(60-70 meV)，与链长无关。我们认为，即使在未稀释的薄膜中，斯托克斯位移也可以用来估计噻吩衍生物中激子迁移的大小。
The intrinsic intrachain photoluminescence (PL) dynamics of conjugated polymers in the solid state is investigated. We focus on the PL properties of long beta-substituted oligothiophenes (8-mer, 12-mer, and 16-mer) and regio-regular (RR) and regio-random poly(3-octylthiophenes) (P3OTs) diluted in the inactive solid matrix polypropylene (PP). The oligothiophenes have well-resolved 0-0 PL and absorption peaks at 4 K and show a good linear relationship with the reciprocal of the ring number. Franck-Condon analyses on the PL spectra reveal that the strength of the electron-phonon coupling represented by the Huang-Rhys factor becomes weak with increasing chain length in the oligomers. In contrast, the presence of stronger electron-phonon coupling is confirmed in RR P3OT despite it being of a much longer chain length than oligomers. This is probably due to its stereoregular chain conformation. The materials used in this work diluted in PP exhibit single-exponential PL decays with lifetimes that decrease with increases in the chain length. The presence of intrachain exciton migration is shown by the time-resolved PL measurements, except for the case of RR P3OT. The energy shifts attributed to intrachain migration are much smaller than those ascribed to interchain migration. We conclude that a change in the torsion angle around the thiophene ring bonds occurs within 50 ps following the absorption transition in thiophene derivatives and that the torsional change gives rise to a constant Stokes shift (60-70 meV), regardless of the chain length. We propose that the Stokes shift can be utilized for estimating the magnitude of exciton migration in thiophene derivatives, even in the case of undiluted films.