Tomasulo Massimiliano, Kaanumal Sireesha L, Sortino Salvatore, Raymo Françisco M
Center for Supramolecular Science, Department of Chemistry, University of Miami, 1301 Memorial Drive, Florida 33146-0431, USA.
J Org Chem. 2007 Jan 19;72(2):595-605. doi: 10.1021/jo062004d.
We have designed and synthesized four compounds integrating luminescent and photochromic components in their molecular skeletons. Two of them combine a nitrospiropyran photochrome with either one or two naphthalene fluorophores and can be prepared in three synthetic steps. The other two consist of a nitrospiropyran photochrome and a benzophenone phosphore connected by either ether or ester linkages and can be prepared in six or five, respectively, synthetic steps. The luminescent components of these assemblies are expected to transfer energy intramolecularly to the photochromic species upon excitation and encourage their photoisomerization. Consistently, the phosphorescence of the benzophenone units and the fluorescence of the naphthalene components are effectively quenched when these species are connected covalently to a nitrospiropyran. Nonetheless, the photoisomerization of the photochrome becomes significantly less efficient after the covalent attachment to the luminescent partner. The fraction of incident radiations absorbed by either the benzophenone or the naphthalene fragment does not promote the isomerization of the photochromic appendage. Instead, irreversible transformations occur upon irradiation of the luminophore-photochrome assemblies. Thus, the covalent attachment of a benzophenone or a naphthalene to a nitrospiropyran is not a viable strategy to improve the photocoloration efficiency of the photochromic component. Even although the very same luminophores are known to sensitize intermolecularly the isomerization of nitrospiropyrans, the transition to covalent luminophore-photochrome assemblies tends to promote degradation, rather than sensitization, upon irradiation.
我们设计并合成了四种化合物，这些化合物在其分子骨架中整合了发光和光致变色成分。其中两种化合物将硝基螺吡喃光致变色剂与一个或两个萘荧光团结合在一起，可通过三个合成步骤制备。另外两种化合物由硝基螺吡喃光致变色剂和通过醚键或酯键连接的二苯甲酮磷光体组成，分别可通过六个或五个合成步骤制备。这些组装体的发光成分预计在激发时会在分子内将能量转移到光致变色物种上，并促进它们的光异构化。一致地，当这些物种与硝基螺吡喃共价连接时，二苯甲酮单元的磷光和萘成分的荧光会被有效淬灭。然而，在与发光伙伴共价连接后，光致变色剂的光异构化效率显著降低。二苯甲酮或萘片段吸收的入射辐射分数并不能促进光致变色附属物的异构化。相反，在照射发光体-光致变色剂组装体时会发生不可逆的转变。因此，将二苯甲酮或萘与硝基螺吡喃共价连接不是提高光致变色成分光致变色效率的可行策略。即使已知相同的发光体能够分子间敏化硝基螺吡喃的异构化，但在照射时，向共价发光体-光致变色剂组装体的转变往往会促进降解，而不是敏化。
