Theoretical study of charge-transport and optical properties of organic crystals: 4,5,9,10-pyrenedi­imides

This work presents a systematic study of the conducting and optical properties of a family of aromatic di­imides reported recently and discusses the influences of side-chain substitution on the reorganization energies, crystal packing, electronic couplings and charge injection barrier of 4,5,9,10-pyrenedi­imide (PyDI). Quantum-chemical calculations combined with the Marcus–Hush electron transfer theory revealed that the introduction of a side chain into 4,5,9,10-pyrenedi­imide increases intermolecular steric interactions and hinders close intermolecular π–π stacking, which results in weak electronic couplings and finally causes lower intrinsic hole and electron mobility in t-C(5)-PyDI (μ(h) = 0.004 cm(2) V(−1) s(−1) and μ(e) = 0.00003 cm(2) V(−1) s(−1)) than in the C(5)-PyDI crystal (μ(h) = 0.16 cm(2) V(−1) s(−1) and μ(e) = 0.08 cm(2) V(−1) s(−1)). Furthermore, electronic spectra of C(5)-PyDI were simulated and time-dependent density functional theory calculation results showed that the predicted fluorescence maximum of t-C(5)-PyDI, corresponding to an S (1)→S (0) transition process, is located at 485 nm, which is close to the experimental value (480 nm).