# Luminescence Tuning of Fluorinated Bistolanes via Electronic or Aggregated-Structure Control
## 3 Results and Discussion  
### Molecular Design  
Using DFT and TD-DFT calculations in the Gaussian 09 suite of programs, we examined the effect of the terminal substituent in each designed molecule on the electron-density distribution over the entire molecule. The geometries of **1 aB-D** in the ground (S\({}_{0}\)) and excited (S\({}_{1}\)) states were optimized at the CAM-B3 LYP/6-31+G(d) level of theory with the implicit solvation CPCM model for CH\({}_{2}\)Cl\({}_{2}\). Figure 2 shows the structures of **1 aB-D** and their calculated electrostatic potential maps, dipole moments along the long molecular axis (\(\mu_{\parallel}\)), isodensity surfaces, and orbital energies for the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO).  
The electrostatic potential maps of **1 aB-D** reveal that the electron density at the fluorinated aromatic ring decreases in the following order: **1 aB \(>\) 1 aC \(>\) 1 aD**. The dipole moment (\(\mu_{\parallel}\)) along the  
Figure 2: Chemical structures of **1 aB–D** and their electrostatic potential maps, dipole moments (\(\mu_{\parallel}\)) along the long molecular axis, isodensity surfaces with the color-bar (isovalue = 0.0004), and orbital energies for the HOMO and LUMO in the S\({}_{1}\) state.  
long molecular axis can be used to assess the electron-density distribution over the entire molecule quantitatively. AcO-substituted **1 aB** had the smallest \(\mu_{\parallel}\) value (3.48 D), and this value increased when the AcO group was replaced by a CF\({}_{3}\) or CN group (\(\mu_{\parallel}\) = 9.63 D for **1 aB** and 12.2 D for **1 aC**). These results clearly confirm that the incorporation of AcO, CF\({}_{3}\), and CN groups into the fluorinated bistolane scaffold can be used to systematically change the electron-density distribution over the entire molecule. The electron-density distribution also affected the molecular orbitals, with the orbital lobes in the HOMO largely localized on the relatively electron-rich aromatic rings, whereas the LUMO lobes were relatively localized on the electron-deficient aromatic rings. The orbital separation between the HOMO and LUMO in the S\({}_{1}\) state may contributable to unique PL behavior through intramolecular charge transfer [31]. The energy differences (\(\Delta\)E\({}_{\text{H-L}}\)) between HOMO and LUMO levels were 5.08 eV for **1 aB**, 4.89 eV for **1 aC**, and 4.67 eV for **1 aD**. Thus, **1 aD** is expected to show a PL band in the long-wavelength region, with the PL wavelength shifting towards shorter wavelengths as the transition energy increases, i.e., **1 aB** > **1 aC**. Theoretical calculations for **1 bB-D**, bearing long alkoxy substituents, also provided similar \(\mu_{\parallel}\) and HOMO/LUMO distributions (see Supplementary Materials), assuming that the alkoxy-substituent does not affect in the electron density distribution. Consequently, systematic control of the electron-density distribution induced by modulating the electronic character of the terminal substituent should realize luminescence tuning for the fluorinated luminophores. According to our previous study, modulation of terminal substituents also influences the LC behavior [21; 23], not only through changes in the electron-density distribution but also in the steric bulkiness of the substituent. Thus, systematic modulation of the terminal substituent in **1 aB-D** may also allow control of the LC behavior.