Tomasulo Massimiliano, Sortino Salvatore, Raymo Françisco M
Center for Supramolecular Science, Department of Chemistry, University of Miami, 1301 Memorial Drive, Miami, Florida 33146-0431, USA.
J Org Chem. 2008 Jan 4;73(1):118-26. doi: 10.1021/jo7017119. Epub 2007 Dec 6.
We have designed bichromophoric photochromes based on the photoinduced opening and thermal closing of a [1,3]oxazine ring. In particular, we have synthesized six compounds incorporating fused 3H-indole and 4-nitrophenoxy fragments and pendant biphenyl, styryl, biphenylvinyl, or stilbenylvinyl groups. The laser excitation of two of these six molecules cleaves a [C-O] bond and opens their [1,3]oxazine ring in less than 6 ns with quantum yields of 0.08 and 0.28, respectively. This photoinduced process generates simultaneously a 4-nitrophenolate anion and a 3H-indolium cation. Both chromophores absorb in the same region of the electromagnetic spectrum. As a result, an intense band appears at ca. 440 nm upon the photoinduced opening of the [1,3]oxazine ring. In both instances, the photogenerated species switches back to the original isomer with first-order kinetics and lifetimes of 38 and 140 ns, respectively. Both compounds have excellent fatigue resistances and retain their photochemical behavior within rigid poly(methyl methacrylate) matrices. However, the thermal reisomerization within the polymer matrix is significantly slower and requires several microseconds to occur. The other four compounds do not undergo ring opening upon excitation under otherwise identical experimental conditions. Indeed, either photoinduced electron transfer or intersystem crossing compete successfully with the ring-opening process.
我们基于[1,3]恶嗪环的光致开环和热闭环设计了双色发色光致变色化合物。具体而言，我们合成了六种化合物，它们包含稠合的3H-吲哚和4-硝基苯氧基片段以及侧链联苯基、苯乙烯基、联苯乙烯基或二苯乙烯基乙烯基。这六种分子中的两种在激光激发下会在不到6纳秒的时间内断裂[C-O]键并打开其[1,3]恶嗪环，量子产率分别为0.08和0.28。这种光致过程同时产生一个4-硝基酚盐阴离子和一个3H-吲哚鎓阳离子。两种发色团都在电磁光谱的同一区域吸收。因此，在[1,3]恶嗪环光致开环时，在约440纳米处出现一个强吸收带。在这两种情况下，光生物种都以一级动力学分别在38纳秒和140纳秒的寿命内切换回原始异构体。这两种化合物都具有出色的抗疲劳性，并在刚性聚甲基丙烯酸甲酯基质中保持其光化学行为。然而，聚合物基质中的热异构化明显较慢，需要几微秒才能发生。在其他相同的实验条件下，另外四种化合物在激发时不会发生开环。实际上，光致电子转移或系间窜越与开环过程成功竞争。
