Perylene diimides (PDIs) and their derivatives are active n-type semiconducting materials widely used in organic electronic devices. A series of PDI derivatives have been investigated by quantum chemistry calculations combined with Marcus–Hush electron-transfer theory. The substitution of three different sites of a PDI induces large changes in its electron-transfer mobility. 2,5,8,11-Tetrachloro-PDI with four chlorine atoms in ortho positions shows both large electron- and hole-transfer mobilities of 0.116 and 0.650 cm² V⁻¹ s⁻¹, respectively, indicative of a potentially highly efficient ambipolar organic semiconducting material. The calculated electron-transfer mobility of 1,6,7,12-tetrachloro-PDI is 0.081 cm² V⁻¹ s⁻¹, which is in good agreement with the experimental result. Octachloro-PDIs have the largest electron mobility among these derivatives, although the π system of the central core is twisted. 2D π-stacking and hydrogen bonds formed at the imide positions are responsible for the large mobility. Simulated anisotropic transport mobility curves of these materials prove the magnitude of the mobility that appears when the measuring transistor channel is along the a-axis of the crystal, which is the direction of hydrogen bond formation.

Experimental and theoretical methods were used to study newly synthesized thiophene-π-conjugated donor–acceptor compounds, which were found to exhibit efficient intramolecular charge-transfer emission in polar solvents with relatively large Stokes shifts and strong solvatochromism. To gain insight into the solvatochromic behavior of these compounds, the dependence of the spectra on solvent polarity was studied on the basis of Lippert–Mataga models. We found that intramolecular charge transfer in these donor–acceptor systems is significantly dependent on the electron-withdrawing substituents at the thienyl 2-position. The dependence of the absorption and emission spectra of these compounds in methanol on the concentration of trifluoroacetic acid was used to confirm intramolecular charge-transfer emission. Moreover, the calculated absorption and emission energies, which are in accordance with the experimental values, suggested that fluorescence can be emitted from different geometric conformations. In addition, a novel S₂ fluorescence phenomenon for some of these compounds was also be observed. The fluorescence excitation spectra were used to confirm the S₂ fluorescence. We demonstrate that S₂ fluorescence can be explained by the calculated energy gap between the S₂ and S₁ states of these molecules. Furthermore, nonlinear optical behavior of the thiophene-π-conjugated compound with diethylcyanomethylphosphonate substituents was predicted in theory.