理论计算解释单分子不发射荧光，得到S1振子强度几乎为零，但HOMO与LUMO重叠度很大

Poe

1：背景介绍：通过计算解释单分子不发光，计算了基态结构优化和频率分析，激发态几何优化和频率分析都正常收敛，无虚频
2：问题：通过借助b3lyp泛函，优化了第一激发态，振子强度几乎都为零，但是HOMO和LUMO轨道几乎完全重叠，请问这种情况是否正常？
Excited State   1:      Singlet-?Sym    1.2892 eV  961.68 nm  f=0.0001  <S**2>=0.000
     152 ->153         0.70642
This state for optimization and/or second-order correction.
Total Energy, E(TD-HF/TD-KS) =  -1840.47645239   
Copying the excited state density for this state as the 1-particle RhoCI density.
Excited state symmetry could not be determined.
Excited State   2:      Singlet-?Sym    3.0993 eV  400.04 nm  f=0.0000  <S**2>=0.000
     151 ->153        -0.70700
Excited state symmetry could not be determined.
Excited State   3:      Singlet-?Sym    3.4479 eV  359.60 nm  f=0.0008  <S**2>=0.000
     152 ->154        -0.69362
     152 ->157         0.13186
S1的振子强度几乎为零，实验结果也是无荧光发射，但是HOMO和LUMO轨道几乎完全重叠

想问问各位老师，这种情况是否正常，或者有什么合理的解释呢？

catenarygong

Sorry my computer cannot input Chinese
As your figure displayed, the LUMO orbitals is mostly like the conjugated-pi orbitals of the right segment.
But the HOMO orbitals is mostly like the sigma orbitals, which is mostly vertical to the pi orbitals.

Poe

catenarygong 发表于 2019-1-18 13:10
Sorry my computer cannot input Chinese
As your figure displayed, the LUMO orbitals is mostly like t ...

十分感谢你的回复。LUMO轨道是pi*轨道，HOMO轨道是sigma轨道，这个过程是一个宇称禁阻的过程，所以振子强度几乎为零，而且不发射荧光，这么理解可以吗？

我本是个娃娃

Poe 发表于 2019-1-18 15:24
十分感谢你的回复。LUMO轨道是pi*轨道，HOMO轨道是sigma轨道，这个过程是一个宇称禁阻的过程，所以振子强 ...

Please try to use the functionals such as M06-2X or wB97XD.
Sometimes, B3LYP is not fitted to TD-DFT.

Poe

我本是个娃娃 发表于 2019-1-19 14:41
Please try to use the functionals such as M06-2X or wB97XD.
Sometimes, B3LYP is not fitted to TD- ...

好的，我去试试看，谢谢老师