1,8-萘酰亚胺类衍生物的结构特性对其吸收和发射光谱影响的密度泛函研究

利用B3LYP/6-31G(d)方法优化了一系列N取代1，8-萘酰亚胺类物质的结构，利用含时密度泛函TD-B3LYP/6-31+G(d)方法及C-PCM模式，计算了它们在气相及二氯甲烷溶剂中的吸收和发射光谱。利用计算得出的前线轨道电子云分布及其对应的能级对它们的取代基对电子吸收光谱的影响进行了讨论。结果表明：此种方法计算出的二氯甲烷溶剂中的1，8-萘酰亚胺的吸收光谱与实验光谱比较吻和。取代CO基团的CN基团及其成环在吸收光谱和发射光谱中发挥了重要的作用。酰亚胺结构上的改性即CN基团的引入及在萘环上取代基一方面引入了结构上的不对称性，导致了衍生物的偶极矩的增大;同时结构上的改性扩展了萘酰亚胺共轭结构。4位取代NO₂衍生物从基态到第一激发态的Mulliken原子电荷比5位多一些，这意味着5位取代NO₂衍生物提供了较多的电子。对N(Ph)₂ 和N(Me)₂衍生物而言，他们4位取代衍生物提供了更多的电荷。前线轨道电子云表明：OCNCN基团改性扩展和N(Me)₂, N(Ph)₂和NO₂取代基拓展了这类分子的π—π*跃迁范围，从而使得前线轨道能级差降低，它们的吸收和发射光谱也发生了一定程度的红移。对给体取代基而言，它们的4位是电子传输态;对受体取代基NO₂而言，它们的5位是电荷传输态。当NO₂基团与CO基团在同一侧及当N(Me)₂和N(Ph)₂与在CN在同一侧时，此类化合物具有较好的传导特性。从化合物1到4，吸收光谱红移了139 nm。电荷传输越明显，吸收光谱红移的就越多。OCNCO的结构改性及其电荷传输机理为今后的萘酰亚胺类物质的分子设计提供了设计理论依据。

Structural Effect on Absorption and Emission Properties of 1,8-Naphthalimide Derivatives:a DFT Study

Using B3LYP/6-31G(d) model, time depended(TD)-B3LYP/6-31+G(d) method and Conductor-like Polarizable Continuum Model (C-PCM)-TD-B3LYP/6-31+G(d) method, we calculated the structure and the absorption and emission spectra of a series of N-substituted 1,8-naphthalimides in both gas-phase and dichloromethane. The influence of the substituents on the electronic absorption spectra and their emission spectra has been discussed on their calculated frontier molecular orbitals contour and their energy levels. Results show that their rings extension from CN group and the substituents on their naphthalimic ring play an important role in the absorption spectra and the emission spectra properties. Modification of OCNCO group and the substituents in their naphthalimic rings breaks the structural symmetry. The Mulliken atomic charges values of NO₂ groups from S0 to S1 in 4 positions are a little greater than the 5-positions, which also mean that the 5 position provide more electrons. For MACs of N(Ph)₂ and N(Me)₂, the 4 position substituents provide more charges than that of 5 position. They not only lead to bigger dipole moments, but also extend frontier orbital contour. Frontier orbitals also show that the modification of OCNCN and the introduction N(Me)₂, N(Ph)₂ and NO₂ groups extends their π—π* excitation scope and decreases their energy gap accordingly. Besides, those kinds of molecular design enhance intra molecular charge transfer between substituent and naphthalimic ring. Therefore, redshift are shown in their absorption and emission spectra, which is also verified by calculated results. Their absorption and emission spectra in solvent redshift compared with their gas spectra. For the NO₂ derivatives, the charge transfer state is in the 5 position substituent compounds. For donor substituents, charge transfer state lies in their 4 position compounds. When the CO group is in the same side with the NO₂ group, and the N(Me)₂ and the N(Ph)₂ are in the different side with the CO group, compounds have better conduction properties. From compound 1 to compound 4, the redshift of the absorption spectra in dichloromethane is about 139 nm. The more intramolecular charge transfer, the bigger absorption maximum those compounds shown. Above result is in good agreement with the 5-position NO₂ derivatives and the 4-position N(Me)₂, N(Ph)₂ derivatives. Above OCNCO structural change and their charge transfer mechanism provide design basis for further 1,8-naphthalmic derivatives.