用能量转移探测萘-蒽二元分子体系的构象变化

合成了一个带有末端取代的能量给体-萘和能量受体-蒽的开链冠醚（DSA）.吸收光谱表明两个发色团之间在基态时没有相互作用.选择性激发萘观察到萘的荧光强度下降， 同时伴随着蒽的发射增强， 表明发生了从萘至蒽的单重态-单重态能量转移.能量转移效率受溶剂极性的影响.可以认为在极性小的溶剂如苯中－OCH2CH2O－单元中的中心C－C键主要以反式存在，而在极性大的溶剂如乙腈中则以邻交叉式为主.因此，开链冠醚末端取代的萘和蒽之间的距离随着溶剂极性的增大，能量转移效率却随之降低.表明能量转移可以用于探测以柔性配体键连接的给体-受体体系在不同极性溶剂中的构象变化特性.

Using Energy Transfer to Probe Solvent Dependent Conformational Changes in a D-A Podand

A podand carrying terminal naphthalene as energy donor and anthracene as energy acceptor groups (DSA) has been synthesized. Absorption spectroscopy showed that there was no intramolecular interaction between the two chromophores in ground state. Selective excitation of the naphthalene moiety a decrease in the naphthalene fluorescence is observed accompanied by an increase in the anthracene emission. The results indicate that singlet-singlet energy transfer from naphthalene to anthracene occurs. It is demonstrated that the efficiency of energy transfer is influenced by the solvent polarity attributed to the differences in the conformation about the central C - C bond of the - OCH2CH2O - unit which is predominantly trans in low-polarity solvent such as benzene but predominantly gauche in high-polarity solvent such as acetonitrile. This in turn is expected to lead to variations of the naphthalene-anthracene separation that effects energy transfer efficiency. It is concluded that energy transfer can be used as a diagnostic tool to probe solvent-specific conformational properties of a D-A system with a flexible bridging ligand.