Electroabsorbance and Electrofluorescence Analysis of 1,7-, 1,6-, and 1,6,7- Derivatives of Dodecylthio Perylene Diimides

Perylene diimides (PDIs) are an extensively researched class of organic chromophores, known for their tunable electronic absorption spectra, high fluorescence quantum yields, and excellent photochemical stability. We recently synthesized and characterized the photophysical properties of 1,6-, 1,7-, and 1,6,7- derivatives of dodecylthio-N,N′-(2,4-diisopropylanaline)-3,4,9,10-perylenetetracarboxylic diimide (1,6-ThioPDI, 1,7-ThioPDI, and 1,6,7-ThioPDI). The three derivatives displayed noticeable differences in their electronic absorption and fluorescence spectra, excited-state lifetimes, and differences in dipole moments between the ground and excited states, as determined by the Lippert-Mataga analysis method. Herein, electroabsorption (EA) and electrofluorescence (EF) spectroscopy were employed to characterize the changes in polarizability and dipole moments between the ground and excited states. EA and EF spectra of ThioPDI derivatives are dominated by relatively large polarizability changes (Δα̿) with smaller contributions from a change in dipole moment (Δμ⃗). The absolute magnitude of the dipole moment change (|Δμ⃗|) ranges from 2.1 to 3.7 D for the ThioPDI derivatives for the S₁ state. TD-DFT calculations support the EA and EF results and are consistent with a small degree of charge transfer from the thio substituents to the perylene core for the S₁ state. Notably, charge transfer in 1,6-ThioPDI is largely aligned within the perylene plane, whereas it is oriented orthogonal in 1,7-ThioPDI and 1,6,7-ThioPDI due to the different arrangements of the thioether substituents.