Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
Phys Chem Chem Phys. 2018 Sep 19;20(36):23195-23201. doi: 10.1039/c8cp04329a.
Single-molecule fluorescence emission of certain positive photochromic systems such as diarylethenes have been exploited for biological imaging and optical memory storage applications. However, there is a lack of understanding if negative photochromic systems can be used for such type of applications. Hence, to explore the potential of negative photochromic molecules for possible optical memory storage applications, we have here synthesized and studied a series of four norbornadiene-quadricyclane (NBD-QC) photoswitching molecules. These molecules feature either linearly conjugated or cross-conjugated pi-electron systems. Upon photoisomerization, the UV-vis absorption spectra of the molecules revealed a strong blue shift in the QC-form, with a photoisomerization quantum yield close to 80% for the cross-conjugated systems. In contrast, a strong intrinsic emission (up to Φf = 49%) for the linearly conjugated compounds in the NBD form was observed. Upon light-induced isomerization, the emission was completely turned off in the QC-form in all the compounds studied. Further, the robustness of the system was evaluated by performing several switching cycles. Under nitrogen, the emission can be turned off and recovered with almost no loss of emission. We also show that the QC-form can be photochemically triggered to convert back to the NBD-form using a low energy UV light (340 nm), allowing an all optical conversion to both species. The demonstrated properties can make the NBD-QC system attractive for potential applications such as optical memory storage devices.
某些正光致变色体系（如二芳基乙烯）的单分子荧光发射已被用于生物成像和光存储应用。然而，对于负光致变色体系是否可以用于此类应用，目前还缺乏了解。因此，为了探索负光致变色分子在可能的光存储应用中的潜力，我们在这里合成并研究了一系列四环壬烷-双环[2.2.1]庚烷（NBD-QC）光致开关分子。这些分子具有线性共轭或交叉共轭的π电子体系。光致异构化后，分子的紫外可见吸收光谱显示 QC 形式发生了强烈的蓝移，交叉共轭体系的光致异构化量子产率接近 80%。相比之下，在 NBD 形式下，线性共轭化合物表现出强烈的固有发射（高达Φf = 49%）。光诱导异构化后，在所有研究的化合物中，在 QC 形式下，发射完全关闭。此外，通过进行多次开关循环来评估系统的稳健性。在氮气中，发射可以关闭并恢复，几乎没有发射损失。我们还表明，QC 形式可以用光化学触发，使用低能量的 UV 光（340nm）转换回 NBD 形式，允许两种物质的全光学转换。所展示的性质使 NBD-QC 体系成为潜在应用（如光学存储设备）的有吸引力的选择。
