Cyclopentene ring effects in cyanine dyes: a handle to fine-tune photophysical properties

The aim of this study is to investigate the photophysical properties of a cyanine dye analogue by performing first-principles calculations based on density functional theory (DFT) and time dependent-DFT. Cationic cyanine dyes are the subject of great importance due to their versatile applications and the tunability of their photophysical properties, such as by modifying their end groups and chain length. An example of this is the vinylene shift, which is experimentally known for these molecules, and it consists of a bathochromic (red) shift of approximately 100 nm of the 0–0 vibronic transition when a vinyl group is added to the polymethine chain. Our study shows that when the saturated moiety C2H4 of the cyclopentene ring is added to the chain, it interacts with the conjugated π-system, resulting in a smaller HOMO–LUMO gap. Here, we demonstrate the origin of this interaction and how it can be used to fine tune the absorption energies of this class of dyes.


Figure S4 :
Figure S4: Theoretical absorbance spectra for molecules 3(n) with n=1 to 4 in gas phase at TD-DFT/B3LYP/TZP level with 5 excited states.The inset shows the basic structure for the molecule.

)Figure S6 :
Figure S6: Theoretical absorbance spectra for molecules 2(n) with n=1 to 4 in solvent ODCB at TD-DFT/B3LYP/TZP level with 5 excited states.The inset shows the basic structure for the molecule.

Figure S8 :Figure S9 :
Figure S8: Energy difference between different conformers.For the first group (n=odd), trans-trans conformer is more stable.For the second group (n=even), trans-cis conformer is more stable.

Table S1 :
Table comparing the vertical excitation transitions S0-S1 at CC2 and TD-DFT level for molecules 8(n) with n=1 to 4.

Table S6 :
Vertical excitation transitions (eV), main orbitals electronic transitions and oscillator strength (f osc ) for molecules 2(n) with n=1 to 4 in solvent ODCB at TD-DFT/B3LYP/TZP level.The main orbitals involved in the first excitation of each molecule are its HOMO and LUMO.

Table S7 :
Vertical excitation transitions (eV), main orbitals electronic transitions and oscillator strength (f osc ) for molecules 2(n) trans-cis, with n=1 to 8 in gas phase at TD-DFT/B3LYP/TZP level.The main orbitals involved in the first excitation of each molecule are its HOMO and LUMO.

Table S8 :
Vertical excitation transitions (eV), main orbitals electronic transitions and oscillator strength (f osc ) for molecules 8(n) with n=1 to 6 in gas phase at TD-DFT/ω97BX/TZP level.The main orbitals involved in the first excitation of each molecule are its HOMO and LUMO.

Table S9 :
Vertical excitation transitions (eV), main orbitals electronic transitions and oscillator strength (f osc ) for molecules 8(n) with n=1 to 6 in gas phase at TD-DFT/CAM-B3LYP/TZP level.The main orbitals involved in the first excitation of each molecule are its HOMO and LUMO.

Table S12 :
Vertical excitation transitions (eV), main orbitals electronic transitions and oscillator strength (f osc ) for molecules 8(n) with n=1 to 6 in gas phase at TD-DFT/B3LYP/AUG/ATZP level.The main orbitals involved in the first excitation of each molecule are its HOMO and LUMO.7.5 ωB97X/AUG/ATZP

Table S13 :
Vertical excitation transitions (eV), main orbitals electronic transitions and oscillator strength (f osc ) for molecules 8(n) with n=1 to 6 in gas phase at TD-DFT/ωB97X/AUG/ATZP level.The main orbitals involved in the first excitation of each molecule are its HOMO and LUMO.

Table S14 :
Vertical excitation transitions (eV), main orbitals electronic transitions and oscillator strength (f osc ) for molecules1 1-8(n) in gas phase at TD-DFT/B3LYP/TZP level.The main orbitals involved in the first excitation of each molecule are its HOMO and LUMO.