Tuning of the Electro-Optical Properties of Tetraphenylcyclopentadienone via Substitution of Oxygen with Sterically-Hindered Electron Withdrawing Groups

In this report, the substitution of the oxygen group (=O) of Tetraphenylcyclopentadienone with =CR₂ group (R = methyl ester or nitrile) was found to have tuned the electro-optical properties of the molecule. Although both groups are electrons withdrawing in nature, their absorption from UV-vis spectra analysis was observed to have been blue-shifted by methyl ester substitution and red-shifted by nitrile substitution. Interestingly, these substitutions helped to enhance the overall intensity of emission, especially in the context of methyl ester substitution whereby the emission was significantly boosted at higher concentrations due to hypothesized restrictions of intramolecular motions. These observations were explained through detailed descriptions of the electron withdrawing capability and steric properties of the substituents on the basis of density functional theory calculations.