Steady state photolysis of tetraphenylborate salts of meso-2,4-bis(4-(4-nitrostyryl)pyridiniumyl)pentane and 1,3-bis(4-(4-nitrostyryl)pyridiniumyl)propane has been studied by absorption and electron paramagnetic resonance (EPR) spectroscopy in solution at room temperature. The absorption spectra of these compounds upon irradiation at 405 nm in an inert atmosphere showed a strong peak in the visible region and two broad peaks in the near infrared (NIR) region. The meso-2,4-pentane derivative caused stronger electronic interaction between a photogenerated styrylpyridinyl radical and a parent styrylpyridinium cation, and hence showed two slightly blue shifted NIR bands around 920 and 1734 nm compared with those in the 1,3-propane derivative. During storage in the dark, the NIR absorption peak at longer wavelength gradually changed its shape and showed a new band at 1559 nm, which increased until 20 h and was maintained over 100 h. The nature of electronic interactions
responsible for such specific NIR bands was studied in detail spectroscopically. EPR spectra clearly indicated that the unpaired electron was not shared completely between two chromophores as in a normal dimer radical cation but was exchanged rather rapidly between them, probably due to the conformational confinement at one end of these molecules.
通过吸收和电子顺磁共振(EPR)光谱研究了室温下溶液中介于 2,4-双(
4-(4-硝基苯基)吡啶鎓基)
戊烷和 1,3-双(
4-(4-硝基苯基)吡啶鎓基)
丙烷的四苯基
硼酸盐的稳态光解。这些化合物在惰性气氛中经 405 纳米波长照射后的吸收光谱在可见光区显示出一个强峰,在近红外(NIR)区显示出两个宽峰。与 1,3-
丙烷衍
生物相比,介-2,4-
戊烷衍
生物在光生
苯乙烯吡啶基自由基和母体
苯乙烯吡啶阳离子之间产生了更强的电子相互作用,因此在 920 纳米和 1734 纳米附近出现了两个略微蓝移的近红外波段。在黑暗中储存期间,较长波长的近红外吸收峰逐渐改变了形状,并在 1559 nm 处出现了一个新的波段,该波段在 20 h 前不断增加,并在 100 h 内保持不变。EPR 光谱清楚地表明,两个发色团之间并不像正常的二聚自由基阳离子那样完全共享未配对电子,而是在它们之间快速交换,这可能是由于这些分子一端的构象限制所致。