Department of Chemistry and Chemical Biology, University of New Mexico, MSC03 2060, Albuquerque, New Mexico 87131, USA.
J Chem Phys. 2010 Nov 7;133(17):174901. doi: 10.1063/1.3500658.
Optical emission spectra of poly[2-methoxy-5-[3('),7(')-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) in dilute solutions exhibit a vibronic progression interval (∼1225 cm(-1)) that does not correspond to any ground state vibrational mode frequency. This phenomenon is assigned as the missing mode effect (MIME) in which five key displaced polymer backbone vibrational modes in the range of 800-1600 cm(-1) contribute to the MIME interval. Emission spectra are calculated by analytically solving the time-dependent Schrödinger equation using estimates of mode-specific vibrational displacements determined independently from preresonance Raman intensities. Emission spectra of MDMO-PPV thin films and nanoparticles are measured and lineshapes show an increase of the MIME frequency to ∼1340 cm(-1) in addition to changes in vibronic intensity distributions and energies. Composite blend thin films consisting of MDMO-PPV and a fullerene derivative (1:1 w/w) exhibit a substantially larger MIME interval (∼1450 cm(-1)) that arises from an increase in polymer chain planarity. This structural change is most apparent from large decreases of the excited state displacement of an out-of-plane C-H bending mode (961 cm(-1)) that becomes forbidden in the planar structure.
聚[2-甲氧基-5-[3'（），7'（）-二甲辛氧基]-1,4-亚苯基乙烯基]（MDMO-PPV）在稀溶液中的光发射光谱显示出一个振子间隔（1225cm-1），与任何基态振动模式频率都不对应。这种现象被分配为缺失模式效应（MIME），其中五个关键的聚合物主链在 800-1600cm-1 范围内的位移振动模式对 MIME 间隔有贡献。发射光谱通过分析求解时变薛定谔方程来计算，使用独立于预共振拉曼强度确定的模式特定振动位移的估计值。测量了 MDMO-PPV 薄膜和纳米颗粒的发射光谱，谱线形状显示 MIME 频率增加到1340cm-1，同时还改变了振子强度分布和能量。由 MDMO-PPV 和富勒烯衍生物（1:1w/w）组成的复合共混薄膜表现出更大的 MIME 间隔（~1450cm-1），这是由于聚合物链平面性的增加。这种结构变化最明显的表现是平面结构中禁止的面外 C-H 弯曲模式（961cm-1）的激发态位移大大减小。
