PICOSECOND FLUORESCENCE AND 2-STEP LIF STUDIES OF THE EXCITED-STATE PROTON-TRANSFER IN METHANOL SOLUTIONS OF 7-HYDROXYQUINOLINE AND METHYL-SUBSTITUTED 7-HYDROXYQUINOLINES
PICOSECOND FLUORESCENCE AND 2-STEP LIF STUDIES OF THE EXCITED-STATE PROTON-TRANSFER IN METHANOL SOLUTIONS OF 7-HYDROXYQUINOLINE AND METHYL-SUBSTITUTED 7-HYDROXYQUINOLINES
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DOI：
10.1021/ja00135a013
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发表时间：
1995-08-02
影响因子：
15
通讯作者：
ITOH, M
中科院分区：
文献类型：
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作者：
NAKAGAWA, T;KOHTANI, S;ITOH, M
7-羟基喹啉（7-HQ）和6-甲基取代的7-HQ（6-Me-7-HQ）的甲醇溶液具有紫外（λ（max）370-390 nm）和大斯托克斯位移（λ（max）510-520 nm）的荧光光谱。前者和后者归因于正常（1：1和1：2氢键复合物）和互变异构体的荧光光谱。皮秒荧光和纳秒/皮秒两步激光诱导荧光表明，这些化合物的互变异构体荧光是通过1：2氢键复合物中的激发态质子转移（ESPT）产生的。7-羟基-8-甲基喹啉（8-Me-7-HQ）的甲醇溶液显示出相当宽的紫外荧光（λ（max）类似于400 nm）而没有互变异构体荧光。这些化合物的吸收光谱的浓度依赖性（甲醇/己烷）和pK（a）测定表明，7-HQ和6-Me-7-HQ可能形成1：2的H-键合复合物，导致ESPT，而8-Me-7-HQ仅形成1：1的H-键合复合物，没有显著的ESPT。考虑到6-和8-甲基的空间位阻因素，7-羟基和环氮原子的顺式构象似乎是形成1：2氢键复合物所必需的，从而导致7-HQ及其甲基取代化合物在醇溶液中的ESPT。
The methanol solutions of 7-hydroxyquinoline (7-HQ) and 6-methyl-substituted 7-HQ (6-Me-7-HQ) exhibit UV (lambda(max) 370-390 nm) and large Stokes shifted (lambda(max) 510-520 nm) fluorescence spectra. The former and latter were ascribed to the normal (1:1 and 1:2 H-bonded complexes) and tautomer fluorescence spectra. Picosecond fluorescence and nanosecond/picosecond two-step LIF demonstrated that the tautomer fluorescence was generated by the excited-state proton transfer (ESPT) in the 1:2 H-bonded complexes of these compounds. The methanol solution of 7-hydroxy-8-methylquinoline (8-Me-7-HQ) shows a considerably broad UV fluorescence (lambda(max) similar to 400 nm) without the tautomer fluorescence. Concentration dependence (methanol/hexane) of absorption spectra and pK(a) determination of these compounds indicated that 7-HQ and 6-Me-7-HQ probably form 1:2 H-bonded complexes leading to the ESPT, while 8-Me-7-HQ forms only 1:1 H-bonded complex exhibiting no significant ESPT. Taking account of the steric factor of the 6- and 8-methyl groups, the cis conformation of the 7-OH group and the ring nitrogen atom seems to be required for 1:2 H-bonded complex formation leading to the ESPT in alcohol solutions of 7-HQ and its methyl-substituted compounds.