Theoretical studies on 4H-cyclopenta[2,1-b:3,4-b′]dithiophene-based Windmill-shaped nanogrids with low reorganization energies

A new kind of organic charge transport nanomolecule, 4H-cyclopenta[2,1-b:3,4-b′]dithiophene-based windmill-shaped nanogrid called WG-CPDT, and its corresponding derivatives substituted by ethynyl, cyano, fluorine and methyl groups at 1-position of CPDT moiety, was designed and studied theoretically. The density functional theory (DFT) was then employed to investigate the molecular structures and electronic properties such as molecular orbitals, ionization potentials (IPs), electron affinities (EAs), reorganization energies (λ). Furthermore, the noncovalent interaction analysis and the normal mode analysis were utilized to estimate the intramolecular weak interactions and the contributions of each vibrational modes to reorganization energies, respectively. The results indicate that WG-CPDT possesses a small reorganization energy in the electron transfer process, and that WG-CPDT is a kind of potential organic electron transport material. This is especially notable when WG-CPDT is modified with cyano on the 1-position of the CPDT moiety and the electron reorganization energies decrease to 0.099 eV. In addition, the delocalization of LUMO near C(sp³) position is consistent with the S⋯π and C–H⋯π weak interactions, which favors good electron transport properties. This work provides new insights into a type of bulky macrocycle in charge transport materials.