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The synthesis, separation, and characterization of 1,6-, 1,7-, and 1,6,7- derivatives of dodecylthio–N,N’– (2,4–diisopropylphenyl)-3,4,9,10-perylenetetracarboxylic diimide are reported. The three derivatives display noticeable differences in their electronic absorption and emission properties, with a bathochromic shift in spectral maxima from 1,6–Thio–PDI, to 1,7–Thio–PDI, to 1,6,7–Thio–PDI. The 1,7–Thio–PDI derivative had the highest fluorescence quantum yield and longest fluorescence lifetime in toluene (ΦF = 0.85, τF = 8.3 ns), followed by 1,6–Thio–PDI (ΦF = 0.54, τF = 6.6 ns) and 1,6,7–Thio–PDI (ΦF = 0.16, τF = 4.4 ns). The difference in dipole moment between the ground and excited states were estimated by the Lippert-Mataga analysis of solvent dependent absorption and emission properties and ranged from Δμ = 7.1 Debye for 1,6,7–Thio–PDI to 8.3 Debye for 1,6–Thio–PDI. These measurements were supported by time–dependent density functional theory calculations, which helped interpret the differences in absorption spectra. Cyclic voltammetry showed minor differences in the reduction potentials for the singly and doubly reduced states. The absorption spectra of the singly and doubly reduced states are also reported.