Department of Chemistry, University of Miami, 1301 Memorial Drive, Coral Gables, Florida 33146-0431, USA.
Photochem Photobiol Sci. 2010 Feb;9(2):136-40. doi: 10.1039/b9pp00114j. Epub 2009 Dec 9.
In search of strategies to operate photochromic compounds in aqueous environments, we synthesized two oxazines with a pendant oligo(ethylene glycol) chain each and a co-polymer with multiple oxazine and oligo(ethylene glycol) tails appended to a common macromolecular backbone. The hydrophilic character of the oligo(ethylene glycol) chains imposes solubility in water on two of the three systems. Their laser excitation in water opens the oxazine ring in less than 6 ns to generate zwitterionic isomers able to absorb in the visible region of the electromagnetic spectrum. The photogenerated species revert spontaneously back to the original forms with first-order kinetics. The transition from organic solvents to aqueous environments, however, causes a five-fold decrease in the quantum yield of the photoinduced ring-opening process and elongates the lifetime of the photogenerated isomer from the nanosecond to the microsecond domain. These hydrophilic and photochromic switches can be interconverted hundreds of times between their two states with no sign of degradation in water. As a result, our structural design for the realization of water-soluble photochromic compounds can lead to the development of viable strategies to modulate the structures and functions of biomolecules with microsecond switching times and excellent fatigue resistances under the influence of optical stimulation.
为了寻找在水相环境中操作光致变色化合物的策略，我们合成了两个带有侧链的恶嗪，每个恶嗪都带有一个支链的聚乙二醇链，以及一个带有多个恶嗪和聚乙二醇尾巴的共聚物，这些尾巴都连接到一个共同的大分子主链上。聚乙二醇链的亲水性使其中两个系统在水中具有可溶性。它们在水中的激光激发不到 6 纳秒就打开恶嗪环，生成能够在电磁光谱可见光区域吸收的两性离子异构体。光致生成的物质以一级动力学自发回复到原始形式。然而，从有机溶剂到水相环境的转变会导致光诱导开环过程的量子产率降低五倍，并将光致生成的异构体的寿命从纳秒延长到微秒范围。这些亲水性和光致变色开关可以在它们的两种状态之间进行数百次的相互转换，在水中没有降解的迹象。因此，我们的结构设计实现了水溶性光致变色化合物，可以导致开发可行的策略来调节生物分子的结构和功能，具有微秒的开关时间和在光刺激下的优异耐疲劳性。
