Intramolecular charge transfer with the planarized 4-aminobenzonitrile 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6).
Intramolecular charge transfer with the planarized 4-aminobenzonitrile 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6).
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DOI：
10.1021/ja037544w
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发表时间：
2004-01
影响因子：
15
通讯作者：
K. Zachariasse;S. Druzhinin;Wilfried Bosch;R. Machinek
中科院分区：
文献类型：
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作者：
K. Zachariasse;S. Druzhinin;Wilfried Bosch;R. Machinek
使用平面化氨基苯甲腈 1-叔丁基-6-氰基-1,2,3,4-四氢喹啉 (NTC6) 在从正己烷到乙腈和甲醇的一系列溶剂中观察到快速高效的分子内电荷转移 (ICT) 和双荧光。对于具有 1-异丙基 (NIC6) 和 1-甲基 (NMC6) 基团的相关分子，以及具有甲基 (NMC5)、异丙基 (NIC5) 或叔丁基 (NTC5) 取代基的 1-烷基-5-氰基二氢吲哚，不会发生此类反应。对于这些分子，发现了来自局部激发 (LE) 态的单个荧光带。根据氨基苯甲腈中 ICT 的 PICT 模型，NTC6 相对较小的能隙 DeltaE(S(1),S(2)) 有利于电荷转移反应。对于 NTC6 的 ICT 态，通过溶剂化变色测量获得约 19 D 的偶极矩，类似于 4-(二甲基氨基)苯甲腈 (DMABN) 的 micro(e)(ICT) = 17 D。对于NMC5、NIC5、NTC5、NMC6和NIC6，通过溶剂化显色分析测定出约10D的偶极矩，与DMABN的LE态的偶极矩相同。对于-70℃下乙醚中的NTC6，正向ICT速率常数（1.3 x 10(11) s(-1)）远小于反向反应速率常数（5.9 x 10(9) s(-1)），表明平衡位于ICT一侧。这里给出的结果清楚地表明，当 DeltaE(S(1),S(2)) 足够小时，ICT 可以通过平面化分子（例如 NTC6）很好地发生，这表明氨基相对于分子其余部分的垂直扭曲对于达到具有大偶极矩的 ICT 状态不是必需的。例如，NMC6 中的六元脂环通过相对于 DMABN 增加 DeltaE(S(1),S(2)) 来防止 ICT。
Fast and efficient intramolecular charge transfer (ICT) and dual fluorescence is observed with the planarized aminobenzonitrile 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6) in a series of solvents from n-hexane to acetonitrile and methanol. Such a reaction does not take place for the related molecules with 1-isopropyl (NIC6) and 1-methyl (NMC6) groups, nor with the 1-alkyl-5-cyanoindolines with methyl (NMC5), isopropyl (NIC5), or tert-butyl (NTC5) substituents. For these molecules, a single fluorescence band from a locally excited (LE) state is found. The charge transfer reaction of NTC6 is favored by its relatively small energy gap DeltaE(S(1),S(2)), in accordance with the PICT model for ICT in aminobenzonitriles. For the ICT state of NTC6, a dipole moment of around 19 D is obtained from solvatochromic measurements, similar to micro(e)(ICT) = 17 D of 4-(dimethylamino)benzonitrile (DMABN). For NMC5, NIC5, NTC5, NMC6, and NIC6, a dipole moment of around 10 D is determined by solvatochromic analysis, the same as that of the LE state of DMABN. For NTC6 in diethyl ether at -70 degrees C, the forward ICT rate constant (1.3 x 10(11) s(-1)) is much smaller than that of the back reaction (5.9 x 10(9) s(-1)), showing that the equilibrium is on the ICT side. The results presented here make clear that ICT can very well take place with a planarized molecule such as NTC6, when DeltaE(S(1),S(2)) is sufficiently small, indicating that a perpendicular twist of the amino group relative to the rest of the molecule is not necessary for reaching an ICT state with a large dipole moment. The six-membered alicyclic ring in NMC6, for example, prevents ICT by increasing DeltaE(S(1),S(2)) relative to that of DMABN.