^<17>O-^1H Double resonance study of the mechanism of thermochromism

近年来，热致变色的分子机理引起了人们极大的兴趣。为了利用氧-17核的核四极共振研究热致变色材料热致变色的分子基础，我们根据Slusher-Hahn双共振原理，设计并建造了一台^<17>O-^1H核双共振谱仪。它观测了零磁场下稀有自旋系统^ O和^ N向质子的极化转移的存在和程度<17><14>（场为4.7T，200 Mhz下的^1H共振），观察质子核磁共振谱的Bruker MSL-200 NMR系统，样品拍摄系统在几秒钟内进入零场步速，以及用于消除大约10 mT的剩余磁场的小型螺线管磁体。后两个系统是去年建造和测试的。一个L-C匹配单元， ...更多信息 建立了低频核四极共振的射频磁场，双共振实验通过扫描低频四极共振频率，寻找质子共振信号从稀有自旋系统到质子自旋的极化转移的减弱;整个实验过程通过使用个人计算机系统来自动化，该个人计算机系统的程序由BASIC和汇编语言编码。利用工作站进行数据分析，成功地观测到了结晶乙酰胺中^ N的纯核四极共振信号<14>，而<17><14>在典型的热致变色材料N-亚水杨基苯胺中没有观测到^ O和^ N的明显信号。失败可能归因于由于非常差的质子信号引起的数据的显著大的散射以及由有效弛豫速率引起的质子信号的快速自还原，其掩盖了通过极化转移的质子信号的有效还原。少

Thermochromism has recently been attracted much interest with respect to its molecular mechanisms. In order to investigate the molecular basis of the thermochromism by means of nuclear quadrupole resonance of the oxygen-17 nucleus in thermochromic materials we designed and constructed a ^<17>O-^1H nuclear double resonance spectrometer on the basis of Slusher-Hahn double resonance principle. It observes the existence and the degree of polarization transfer from rare spin systems such as ^<17>O and ^<14>N to proton at zero magnetic field.The apparatus consists of Oxford superconducting magnet (the field is 4.7 T, ^1H resonance at 200Mhz), Bruker MSL-200NMR system which observe the proton nuclear magnetic resonance spectrum, a sample shooting system into zero-fields pace in a few seconds, and the small solenoid magnet for eliminating the residual magnetic field of an amount of about 10 mT.The latter two systems were constructed and tested the last year. An L-C matching unit to supply the … More radio-frequency magnetic field for the low-frequency nuclear quadrupole resonance was constructed.The double resonance experiments search the reduction of the proton resonace signal due to the polrization-transfer from the rare spin system to the proton spins by sweeping the low-frequency quadrupole resonance frequency ; whole experimental procedures were automated by the use of a personal computer system the program for which was coded by the BASIC and the assembler languages. The data analysis were performed by means of a work station.The double resonance system described above was used to observe successfully the pure nuclear quadrupole resonance signals of ^<14>N in crystalline acetamide ; however, we could neither observe any significant signals of ^<17>O nor ^<14>N in N-salicylideneaniline which is typical thermochromic material. The failure may be attributed to significantly large scattering of data due to very poor proton signal and to rapid self-reduction of the proton signal caused by efficient relaxation rate, which concealed the effective reduction of the proton signal by the polarization transfer. Less