Vibrational and rotational structure and excited-state dynamics of pyrene
Vibrational and rotational structure and excited-state dynamics of pyrene
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DOI：
10.1063/1.3270136
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发表时间：
2009-12-14
影响因子：
4.4
通讯作者：
Lin, Sheng Hsien
中科院分区：
文献类型：
--
作者：
Baba, Masaaki;Saitoh, Motohisa;Lin, Sheng Hsien
通过分析超声速射流单振动能级激发的荧光激发光谱和分散荧光光谱，并参考从头算理论计算结果，研究了芘S-0 (1)A(g)和S-1 B-1（3u）态的振动能级结构。两种状态下的振动能量非常相似。我们发现单振动能级激发的分散荧光光谱具有广谱特征，多余能量为730 cm（-1）。这表明，在芘的S-1 B-1（3u）态中，分子内的振动再分配在少量多余能量下有效地发生。我们还观察到0(0)(0)波段的旋转分辨超高分辨率光谱。测定了转动常数，结果表明，芘分子在S-0和S-1态都是平面的，其几何结构在电子激发下没有明显变化。由M-J能级的塞曼分裂引起的旋转线随磁场的展宽非常小，这表明系统间向三重态的交叉很小。较长的荧光寿命表明，内部转换到S-0状态也很慢。我们认为，芘在S-0和S-1态的分子结构和势能曲线的相似性是导致其无辐射缓慢跃迁的主要原因。
Vibrational level structure in the S-0 (1)A(g) and S-1 B-1(3u) states of pyrene was investigated through analysis of fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation in a supersonic jet and through referring to the results of ab initio theoretical calculation. The vibrational energies are very similar in the both states. We found broad spectral feature in the dispersed fluorescence spectrum for single vibronic level excitation with an excess energy of 730 cm(-1). This indicates that intramolecular vibrational redistribution efficiently occurs at small amounts of excess energy in the S-1 B-1(3u) state of pyrene. We have also observed a rotationally resolved ultrahigh-resolution spectrum of the 0(0)(0) band. Rotational constants have been determined and it has been shown that the pyrene molecule is planar in both the S-0 and S-1 states, and that its geometrical structure does not change significantly upon electronic excitation. Broadening of rotational lines with the magnetic field by the Zeeman splitting of M-J levels was very small, indicating that intersystem crossing to the triplet state is minimal. The long fluorescence lifetime indicates that internal conversion to the S-0 state is also slow. We conclude that the similarity of pyrene's molecular structure and potential energy curve in its S-0 and S-1 states is the main cause of the slow radiationless transitions.