Substituent position-dependent photophysics in fluorinated porphycenes

Area of Science:

• Photochemistry and photophysics of macrocyclic compounds.
• Organic chemistry and materials science.

Background:

• Porphycenes are macrocyclic compounds with interesting photophysical properties.
• Fluorine substitution is known to modulate electronic and structural characteristics of organic molecules.

Purpose of the Study:

• To investigate the effect of meso-fluorination on the photophysical properties of porphycenes.
• To correlate structural changes with fluorescence quantum yields and decay times.

Main Methods:

• Synthesis of meso-fluorinated porphycene derivatives.
• Spectroscopic measurements of fluorescence quantum yields and lifetimes.
• Computational calculations of excited state geometries and energies.

Main Results:

• Meso-fluorination position-dependently affects fluorescence; 9,19- and 9,20-difluoroporphycenes show higher quantum yields than 9,10-difluoroporphycenes.
• Increased solvent viscosity enhances fluorescence in weakly emitting porphycenes.
• Computational studies reveal nonplanar structures in the lowest excited singlet state, facilitating rapid depopulation.

Conclusions:

• The photophysical properties of fluorinated porphycenes are strongly influenced by the number and position of fluorine atoms.
• Geometry distortion in the excited state, leading to loss of aromaticity, is proposed as the primary nonradiative deactivation pathway.