Highly Twisted N,N-Dialkylamines as a Design Strategy to Tune Simple Aromatic Hydrocarbons as Steric Environment-Sensitive Fluorophores
Highly Twisted N,N-Dialkylamines as a Design Strategy to Tune Simple Aromatic Hydrocarbons as Steric Environment-Sensitive Fluorophores
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DOI：
10.1021/jacs.6b03749
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发表时间：
2016-07-06
影响因子：
15
通讯作者：
Konishi, Gen-ichi
中科院分区：
文献类型：
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作者：
Sasaki, Shunsuke;Suzuki, Satoshi;Konishi, Gen-ichi
从实验和理论上研究了9，10-双(N，N-二烷氨基)菲类化合物(BDAAs)的空间环境荧光敏感性。提出了一种新的设计策略，将简单芳烃类化合物作为高效的聚集诱导发射(AIE)发光体和分子旋转体。对于多种BDAA，观察到了显著的斯托克斯位移和高效的固体荧光。对BDAA-甲基的计算表明，在基态(S-0)构象中，锥体胺基团高度扭曲，使其孤对轨道不能与菲的pi轨道共轭。荧光发生在S-1的最小值，其中一个或两个胺基是平面化的。S-1激发态极小值的稳定性和S-0态的失稳是产生大斯托克斯位移的原因。非绝热跃迁速率的实验测量表明，二烷氨基(或强给电子基)的对位二取代是快速内转换的关键。发现S-1态和S-0态的最小能量锥交具有类杜瓦-苯结构。虽然在液相中可以有效地实现快速内转换，但需要大幅度的运动才能达到这种MECI，这在固态时是被禁止的，从而导致了高效的AIE。这一策略被用来实验发现，萘类似物也是有效的AIE发光体。氨基上的烷基链的柔性也被发现对于允许的电荷转移转变是重要的。因此，提出了三个点[(1)高扭曲的N，N-二烷胺，(2)对位取代，(3)柔性烷基]来活化小芳烃。
The steric-environment sensitivity of fluorescence of 9,10-bis(N,N-dialkylamino)anthracenes (BDAAs) was studied experimentally and theoretically. A new design strategy to tune simple aromatic hydrocarbons as efficient aggregation-induced emission (AIE) luminogens and molecular rotors is proposed. For a variety of BDAAs, prominent Stokes shifts and efficient solid-state fluorescence were observed. Calculations on BDAA-methyl suggested that in the ground state (S-0) conformations, the pyramidal amine groups are highly twisted, so that their lone-pair orbitals cannot conjugate with the anthracene pi orbitals. Fluorescence takes place from the S-1 minima, in which one or both amine groups are planarized. The stability of the S-1 excited state minima as well as destabilization of the S-0 state is the origin of large Stokes shift. Experimental measurement of the nonadiabatic transition rate suggests that para disubstitution by dialkylamino (or strongly electron-donating) groups is a key for fast internal conversion. Minimum energy conical intersection (MECI) between S-1 and S-0 states was found to have a Dewar-benzene like structure. Although this can be reached efficiently in liquid phase for fast internal conversion, a large amplitude motion is required to reach this MECI, which is prohibited in the solid state and caused efficient AIE. This strategy is used to find experimentally that naphthalene analogues are also efficient AIE luminogens. The flexibility of alkyl chains on amino groups is also found to be important for allowed charge-transfer transition. Thus, three points [(1) highly twisted N,N-dialkylamines, (2) substitution at the para positions, (3) with flexible alkyl groups] were proposed for activation of small aromatic hydrocarbons.