The solvatochromic response of benzo[a]fluorenone in aprotic solvents compared with benzo[b]fluorenone and 9‐fluorenone

Abstract The solvatochromism and possible excited state deactivation pathways of benzo[a]fluorenone were investigated and compared with the related aromatic compounds 9‐fluorenone and benzo[b]fluorenone. These molecules can serve as molecular building blocks with application in light emitting diodes, catalysts, and dye‐sensitized solar cells. A study of the effect changes in aromatic structure might have on their relative photophysical responses is therefore of interest. Steady‐state absorption and emission spectra, Lippert‐Mataga plots, fluorescence lifetimes, and absolute quantum yields were used in tandem with time dependent density functional theory (TD‐DFT) calculations to investigate solvatochromism, excited state decay, and the relative energies of singlet and triplet excited states. It was found that changes in aromaticity affect the energetic order and character of the excited singlet and triplet states differently among these fluorenones as solvent polarity is varied. The observed fluorescence emission from all these molecules can be understood in terms of their relative ability to undergo intersystem crossing. Additional calculations on the related benzo[c]fluorenone predict that its solvatochromic behavior should resemble that of benzo[a]fluorenone.