Johannes Gutenberg-University, Institute of Physical Chemistry, Jakob-Welder-Weg 11, D-55099 Mainz, Germany.
J Phys Chem B. 2010 Feb 4;114(4):1638-47. doi: 10.1021/jp909862x.
Absorption and emission spectra of perylene-3,4-dicarboximide (PMI) and perylene-3,4,9,10-tetracarboxdiimide (PDI) derivatives embedded in a thin polymer film were measured by room-temperature bulk and low-temperature single-molecule spectroscopy. In contrast to bulk line narrowing spectra, the low-temperature single-molecule data allowed to unambiguously resolve the vibrational fine structure of the emission spectra. Additionally, the emission spectra were calculated by quantum chemical methods within the Franck-Condon approximation for various N-substituted derivatives of PMI and PDI. The experimental as well as calculated emission spectra are dominated by two spectral regions of high vibronic activity, a band system ranging from the 0-0 transition (at DeltaE(0-0)) down to 600 cm(-1) below DeltaE(0-0) and a band system between approximately 1250 and 1700 cm(-1) below DeltaE(0-0). Apart from the wavenumber region close to DeltaE(0-0) (down to 100 cm(-1) below DeltaE(0-0)), good agreement is found between the calculated and experimental spectra, allowing a clear-cut assignment of the dominant vibrational modes. There are, however, discrepancies in the intensities in particular for low-frequency vibrational modes. These differences between theory and experiment are tentatively attributed to linear electron-phonon coupling which is completely neglected in the calculations and hindered internal rotation that is not properly accounted for in the harmonic approximation. Furthermore, in the experimental spectra, at the bulk as well as the single-molecule level, significant differences between PMI and PDI are observed which are attributed to stronger interactions with the matrix environment in the case of PMI due to the permanent electric dipole moment of that molecule.
将苝-3,4-二酰亚胺（PMI）和苝-3,4,9,10-四羧酸二酰亚胺（PDI）衍生物嵌入在聚合物薄膜中，通过室温体相和低温单分子光谱测量其吸收和发射光谱。与体相线宽光谱相比，低温单分子数据可以明确分辨出发射光谱的振动精细结构。此外，通过量子化学方法，在 Franck-Condon 近似下，对 PMI 和 PDI 的各种 N-取代衍生物进行了计算。实验和计算发射光谱都主要由两个高振动态活性的光谱区域主导，一个是从 0-0 跃迁（在ΔE(0-0)处）到ΔE(0-0)以下 600 cm(-1)的带状系统，另一个是在大约 1250 和 1700 cm(-1)之间的带状系统。除了接近ΔE(0-0)的波数区域（在ΔE(0-0)以下 100 cm(-1)）之外，计算光谱和实验光谱之间存在良好的一致性，这使得主要振动模式的明确分配成为可能。然而，在特别是低频振动模式的强度方面存在差异。这些理论与实验之间的差异，推测是由于线性电子-声子耦合在计算中完全被忽略，以及在谐波近似中没有适当考虑的内部旋转受到阻碍。此外，在实验光谱中，无论是在体相还是单分子水平，PMI 和 PDI 之间都观察到显著差异，这归因于 PMI 分子的永久电偶极矩导致其与基质环境的相互作用更强。
