异构芘-N-甲基乙酰胺中的超快过程：具有不同耦合强度的氢键诱导静态激基缔合物的形成
Ultrafast Processes in Isomeric Pyrene-N-methylacetamides: Formation of Hydrogen Bond Induced Static Excimers with Varied Coupling Strength
AI总结：
本研究合成两种位点异构的芘甲基乙酰胺分子，发现它们在甲苯中可形成氢键诱导的静态激基缔合物，且取代位点差异导致激子耦合强度和激基缔合物形成速率显著不同。
摘要：
芘基分子在光激发下易于通过自缔合形成激基缔合物。本研究中，在芘核的1位或2位修饰N-甲基乙酰胺基团，分别合成了pyren-1-methylacetamide（PyMA1，芘-1-甲基乙酰胺）和pyren-2-methylacetamide（PyMA2，芘-2-甲基乙酰胺）。在1.0mM浓度的甲苯溶液中，两者经光激发后主要形成静态激基缔合物。稳态光谱研究表明，溶液中PyMA1二聚体的激子耦合远强于其异构体PyMA2。飞秒-皮秒量级的瞬态吸收（TA）测量（fs-TA）显示，PyMA1中强耦合预缔合二聚体的静态激基缔合物形成时间约为560飞秒，而PyMA2中弱耦合预缔合二聚体的激基缔合物形成时间尺度慢得多（约65皮秒）。研究认为，芘环1位或2位引入的甲基乙酰胺基团可形成具有不同激子耦合程度的氢键激基缔合物。
英文摘要：
Pyrene based molecules are inclined to form excimers through self-association upon photoexcitation. In this work, the pyrene core is functionalized with N-methylacetamide group at the position 1 or 2, to develop pyren-1-methylacetamide (PyMA1) and pyren-2-methylacetamide (PyMA2), respectively. Upon photoexcitation, PyMA1 and PyMA2, at 1.0mM, in toluene, have formed predominantly static excimers. The steady state spectroscopic studies have showed that the excitonic coupling of PyMA1 dimers are much stronger in solution than its isomeric counterpart, PyMA2. The transient absorption (TA) measurements over fs-ps regime (fs-TA) showed that the formation of static excimers with the strongly-coupled pre-associated dimers, in PyMA1, happens in approx. 560fs, whereas, the excimers for the weakly-coupled pre-associated dimers in PyMA2 have formed in much slower time scale (approx. 65ps). The introduction of methylacetamide group at the position 1 or 2 on pyrene ring, was believed to have allowed forming hydrogen bonded excimers with different degrees of excitonic coupling.
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