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

近年来，热致变色的分子机制引起了人们的极大兴趣。为了利用热致变色材料中氧-17核的核四极共振来研究热致变色的分子基础，我们在Slusher-Hahn双共振原理的基础上设计并建造了一台^&lt；17&gt；O-^1H核双共振谱仪。该装置由牛津超导磁体(场强为4.7T，200 MHz下的1H共振)、Bruker MSL-200核磁共振系统、几秒钟内进入零场的零场打样系统和消除约10mT剩余磁场的小型螺线管磁体组成。为…提供服务的L-C匹配单元双共振实验通过扫描低频四极共振频率，寻求从稀有自旋系统到质子自旋的极化转移过程中质子共振信号的减少；整个实验过程由个人计算机系统实现自动化，其程序用BASIC和汇编语言编写。利用上述双共振系统成功地观察到了结晶乙酰胺中的纯核四极共振信号，而在典型的热致变色材料N-水杨醛中却没有观察到明显的核四极共振信号。失败的原因可能是由于质子信号非常差而导致数据的大量散射，以及有效驰豫速率导致的质子信号的快速自还原，这掩盖了通过极化转移对质子信号的有效还原。较少

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