Fu Na, Baumes Jeffrey M, Arunkumar Easwaran, Noll Bruce C, Smith Bradley D
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46545, USA.
J Org Chem. 2009 Sep 4;74(17):6462-8. doi: 10.1021/jo901298n.
Mechanical encapsulation of fluorescent, deep-red bis(anilino)squaraine dyes inside Leigh-type tetralactam macrocycles produces interlocked squaraine rotaxanes. The surrounding macrocycles are flexible and undergo rapid exchange of chair and boat conformations in solution. A series of X-ray crystal structures show how the rotaxane co-conformational exchange process involves simultaneous lateral oscillation of the macrocycle about the center of the encapsulated squaraine thread. Rotaxane macrocycles with 1,4-phenylene sidewalls and 2,6-pyridine dicarboxamide bridging units are more likely to adopt boat conformations in the solid state than analogous squaraine rotaxane systems with isophthalamide-containing macrocycles. A truncated squaraine dye, with a secondary amine attached directly to the central C(4)O(2) core, is less electrophilic than the extended bis(anilino)squaraine analogue, but it is still susceptible to chemical and photochemical bleaching. Its stability is greatly enhanced when it is encapsulated as an interlocked squaraine rotaxane. An X-ray crystal structure of this truncated squaraine rotaxane shows the macrocycle in a boat conformation, and NMR studies indicate that the boat is maintained in solution. Encapsulation as a rotaxane increases the dye's brightness by a factor of 6. The encapsulation process appears to constrain the dye and reduce deformation of the chromophore from planarity. This study shows how mechanical encapsulation as a rotaxane can be used as a rational design parameter to fine-tune the chemical and photochemical properties of squaraine dyes.
将荧光深红色双（苯胺基）方酸染料机械封装在利氏型四内酰胺大环化合物中可产生互锁的方酸轮烷。周围的大环化合物具有柔韧性，在溶液中会快速发生椅式和船式构象的交换。一系列X射线晶体结构表明，轮烷的共构象交换过程涉及大环化合物围绕被封装的方酸链中心的同时横向振荡。与具有间苯二甲酰胺大环化合物的类似方酸轮烷体系相比，带有1,4-亚苯基侧壁和2,6-吡啶二甲酰胺桥连单元的轮烷大环化合物在固态时更倾向于采用船式构象。一种截短的方酸染料，其仲胺直接连接到中心C(4)O(2)核上，亲电性比延伸的双（苯胺基）方酸类似物弱，但仍易受化学和光化学漂白的影响。当它被封装为互锁的方酸轮烷时，其稳定性会大大提高。这种截短的方酸轮烷的X射线晶体结构显示大环化合物处于船式构象，核磁共振研究表明船式构象在溶液中得以保持。作为轮烷进行封装可使染料的亮度提高6倍。封装过程似乎限制了染料，并减少了发色团从平面性的变形。这项研究表明，作为轮烷的机械封装如何可以用作合理的设计参数来微调方酸染料的化学和光化学性质。
