Kurth Todd L, Lewis Frederick D
Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA.
J Am Chem Soc. 2003 Nov 12;125(45):13760-7. doi: 10.1021/ja034311w.
The structure, spectroscopy, and photochemistry of N,N'-dimethyl-N,N'-di-1-naphthylurea have been investigated and compared to the properties of the corresponding secondary diarylurea N,N'-di-1-naphthylurea and the tertiary mono arylurea N,N,N'-trimethyl-N'-1-naphthylurea. The crystal structures and solution NMR spectra of the tertiary and secondary dinaphthylureas establish that they adopt folded (E,E) and extended (Z,Z) structures, respectively, both in the solid state and in solution. In solution, the tertiary E,E-dinaphthylurea exists as a mixture of syn and anti conformations separated by a barrier of ca. 14 kcal/mol, as determined by variable-temperature (1)H NMR spectroscopy. Computational exploration of the ground-state potential energy surface suggests that the lowest energy pathway for interconversion of the syn and anti conformers requires concurrent rotation about both the nitrogen-naphthalene and the nitrogen-carbonyl single bonds. The tertiary dinaphthylurea exhibits blue-shifted absorption and red-shifted emission attributed to excitonic interactions between the naphthalene rings. The secondary dinaphthylureas and mono naphthylurea have typical naphthalene-like monomer absorption and fluorescence spectra. Dual exponential fluorescence decay is assigned to the two conformers of the tertiary dinaphthylurea. Nonlinear fitting of the fluorescence decay times provides activation parameters for singlet decay of the two conformers. The decay process is attributed to nonsynchronous naphthalene-naphthalene bonding which, in the case of the syn conformer, results in the formation of a [2+2] intramolecular adduct. The preferred E,E conformation and moderate barrier to conformational isomerization make the tertiary dinaphthylurea an attractive building block for larger self-organizing pi-stacked aromatic arrays.
对N,N'-二甲基-N,N'-二-1-萘基脲的结构、光谱学和光化学性质进行了研究，并与相应的仲二芳基脲N,N'-二-1-萘基脲和叔单芳基脲N,N,N'-三甲基-N'-1-萘基脲的性质进行了比较。叔二萘基脲和仲二萘基脲的晶体结构和溶液核磁共振谱表明，它们在固态和溶液中分别采用折叠的（E,E）结构和伸展的（Z,Z）结构。在溶液中，通过变温（1）H核磁共振光谱测定，叔E,E-二萘基脲以syn和anti构象的混合物形式存在，它们之间的能垒约为14 kcal/mol。基态势能面的计算探索表明，syn和anti构象体相互转化的最低能量途径需要同时围绕氮-萘和氮-羰基单键旋转。叔二萘基脲表现出蓝移吸收和红移发射，这归因于萘环之间的激子相互作用。仲二萘基脲和单萘基脲具有典型的萘状单体吸收和荧光光谱。双指数荧光衰减归因于叔二萘基脲的两种构象体。荧光衰减时间的非线性拟合提供了两种构象体单线态衰减的活化参数。衰减过程归因于非同步的萘-萘键合，在syn构象体的情况下，导致形成[2+2]分子内加合物。优选的E,E构象和适度的构象异构化能垒使叔二萘基脲成为用于更大的自组装π堆积芳香族阵列的有吸引力的构建单元。
