Yang Yonggang, Li Donglin, Li Chaozheng, Liu YuFang, Jiang Kai
College of Physics and Materials Science, Henan Normal University, Xinxiang 453007, China.
College of Physics and Materials Science, Henan Normal University, Xinxiang 453007, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2017 Dec 5;187:68-74. doi: 10.1016/j.saa.2017.06.029. Epub 2017 Jun 23.
Researchers have proposed different effective mechanisms of hydrogen bonding (HB) on the fluorescence of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and its derivatives. Herein, excited state transition and dynamics analysis confirm that the fluorescence of PD (a derivative of PRODAN with ethyl replaced by 3-hydroxy-2,2-dimethylpropan) emits from the planar intramolecular charge transfer (PICT) state rather than twist ICT (TICT) state, because the fluorescence emission and surface hopping from the TICT state to the twist ground (T-S) state is energy forbidden. Nevertheless, the strengthening of intramolecular-HB (intra-HB) and intermolecular-HB (inter-HB) of PD-(methanol) smooth the pathway of surface hopping from TICT to T-S state and the external conversion going to planar ground state by decreasing the energy difference of the two states. This smoothing changes the fluorescence state of PD-(methanol) to the TICT state in which fluorescence emission does not occur but surface hopping, leading to the partial fluorescence quenching of PD in methanol solvent. This conclusion is different from previous related reports. Moreover, the inter-HB strengthening of PD-methanol in PICT state induces the cleavage of intra-HB and a fluorescence red-shift of 54nm compared to PD. This red-shift increases to 66nm for PD-(methanol) for the strengthening of the one intra-HB and two inter-HBs. The dipole moments of PD-methanol and PD-(methanol) respectively increase about 10.3D and 8.1D in PICT state compared to PD. The synergistic effect of intra-HB and inter-HB induces partial quenching of PD in methanol solvent by turning on the TICT state and fluorescence red-shift. This work gives a reasonable description on the fluorescence red-shift and partial quenching of PD in methanol solvent, which will bring insight into the study of spectroscopic properties of molecules owning better spectral characteristics.
研究人员针对氢键（HB）对6-丙酰基-2-二甲基氨基萘（PRODAN）及其衍生物荧光的不同有效机制提出了建议。在此，激发态跃迁和动力学分析证实，PD（PRODAN的一种衍生物，其中乙基被3-羟基-2,2-二甲基丙烷取代）的荧光从平面内分子电荷转移（PICT）态发出，而非扭曲的ICT（TICT）态，这是因为从TICT态到扭曲基态（T-S）态的荧光发射和表面跳跃在能量上是禁阻的。然而，PD-（甲醇）分子内氢键（intra-HB）和分子间氢键（inter-HB）的增强通过减小这两个态的能量差，使从TICT态到T-S态的表面跳跃途径以及向平面基态的外转换变得顺畅。这种顺畅将PD-（甲醇）的荧光态转变为TICT态，在此态中不发生荧光发射但存在表面跳跃，导致PD在甲醇溶剂中的部分荧光猝灭。这一结论与先前的相关报道不同。此外，处于PICT态的PD-甲醇分子间氢键的增强会导致分子内氢键的断裂，与PD相比荧光红移54nm。对于PD-（甲醇），由于一个分子内氢键和两个分子间氢键的增强，这种红移增加到66nm。与PD相比，处于PICT态的PD-甲醇和PD-（甲醇）的偶极矩分别增加约10.3D和8.1D。分子内氢键和分子间氢键的协同作用通过开启TICT态和荧光红移，导致PD在甲醇溶剂中的部分猝灭。这项工作对PD在甲醇溶剂中的荧光红移和部分猝灭给出了合理描述，这将为研究具有更好光谱特性的分子的光谱性质带来启示。
