Department of Physics, Liaoning University, Shenyang 110036, People's Republic of China.
J Phys Chem A. 2010 Feb 11;114(5):2230-4. doi: 10.1021/jp909594e.
The ground-state and excited-state electronic structures as well as the tunable optical properties of a variety of newly designed fluorenone-based molecular materials have been theoretically investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The substitutes on the O atom in the carbonyl group of the fluorenone (FN) molecule with S (FN-C=S), Se (FN-C=Se), and Te (FN-C=Te) atoms can significantly influence their electronic structures, molecular orbitals, geometric conformations, and optical properties of fluorenone-based molecular materials. Due to the important difference of electronegativity for O, S, Se, and Te atoms in the same group, the ground-state dipole moment of these fluorenone-based molecular materials is gradually decreased in the order FN, FN-C=S, FN-C=Se, and FN-C=Te. At the same time, the ground-state bond length of the C=X (X refers O, S, Se, and Te) is gradually increased in the order of FN, FN-C=S, FN-C=Se, and FN-C=Te. Due to the different nature of the S(1) state for FN (pipi* character) and FN-C=S, FN-C=Se, and FN-C=Te (sigmapi* character), the excited-state dipole moment of FN in the S(1) state is dramatically increased in comparison with that in the ground state; however, the excited-state dipole moments of FN-C=S, FN-C=Se, and FN-C=Te are significantly diminished. In addition, the excited-state bond length of C=X (X refers O, S, Se, and Te) in the S(1) state is lengthened in comparison with that in the ground state due to the photoexcitation of the C=X bond FN, FN-C=S, FN-C=Se, and FN-C=Te. On the other hand, the energy level of the HOMO orbital is heightened and that of LUMO orbital is lowered with the introduction of heteroatoms in the order of S, Se, and Te. Consequently, the energy gap between LUMO and HOMO orbtials is gradually decreased in the order of the FN, FN-C=S, FN-C=Se, and FN-C=Te. Consequently, the calculated fluorescence wavelengths are strongly red-shifted from the visible region for FN to the near-infrared (NIR) region for FN-C=S, FN-C=Se, and FN-C=Te. These newly designed fluorenone-based molecules may be potential NIR fluorescent molecular functional materials.
本文采用密度泛函理论（DFT）和含时密度泛函理论（TDDFT）方法，对一系列新设计的基于芴酮的分子材料的基态和激发态电子结构以及可调谐光学性质进行了理论研究。芴酮（FN）分子羰基上的 O 原子被 S（FN-C=S）、Se（FN-C=Se）和 Te（FN-C=Te）取代，可以显著影响其电子结构、分子轨道、几何构象和基于芴酮的分子材料的光学性质。由于同一族中 O、S、Se 和 Te 原子的电负性存在显著差异，这些基于芴酮的分子材料的基态偶极矩逐渐减小，顺序为 FN、FN-C=S、FN-C=Se 和 FN-C=Te。同时，C=X（X 指 O、S、Se 和 Te）的基态键长逐渐增大，顺序为 FN、FN-C=S、FN-C=Se 和 FN-C=Te。由于 FN（pipi* 特征）和 FN-C=S、FN-C=Se 和 FN-C=Te（sigmapi* 特征）的 S(1)态具有不同的性质，FN 在 S(1)态的激发态偶极矩与基态相比显著增加，而 FN-C=S、FN-C=Se 和 FN-C=Te 的激发态偶极矩则显著减小。此外，由于 C=X（X 指 O、S、Se 和 Te）键的光激发，S(1)态中 C=X 键的激发态键长比基态伸长。另一方面，随着杂原子的引入，HOMO 轨道的能级升高，LUMO 轨道的能级降低，顺序为 S、Se 和 Te。因此，FN、FN-C=S、FN-C=Se 和 FN-C=Te 的 LUMO 和 HOMO 轨道能级差逐渐减小。因此，计算出的荧光波长从 FN 的可见光区强烈红移到 FN-C=S、FN-C=Se 和 FN-C=Te 的近红外（NIR）区。这些新设计的基于芴酮的分子可能是潜在的 NIR 荧光分子功能材料。
