Structural, electronic and charge transfer studies of dianthra[2,3-b:2′,3′-f]thieno[3,2-b]thiophene and its analogues: Quantum chemical investigations

The ground state structures of dianthra[2,3-b:2′,3′-f]thieno[3,2-b]thiophene, its derivatives and analogues have been optimized at B3LYP/6-31G** level of density functional theory. The computed geometrical parameters are in good agreement with the experimental data. The decrease in the bond length has been observed in the sequence, SC > BC > OC. The substitution of F and N has no effect to lengthen or shorten the nearest CC or central CC, SC, OC, BC bond lengths. The highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of all the molecules are spread over the whole pi-conjugated backbones with similar character. The HOMOs displays bonding character within each unit while the LUMOs exhibit the antibonding character. By substituting the boron (3), fluoro and nitrogen (4-6) make the LUMOs energy levels lower resulting higher electron mobility. The values of IPv/a and EAv/a increase from 1 to 6 except in 2 where EA decrease but the effect is not so significant. The high EAs of 3 and 6 revealed that these molecules would be more suitable for generating free electron. The positive correlation between EAv and the LUMO levels has been observed. The 3 and 6 would be better as n-type materials having EAs close to 3.0 eV. The electron reorganization energies for 1, 2, 4 and 5 are higher than hole reorganization energies while λe are less than those of λh for 3 and 6. In the last step, we have simulated and successfully regenerated the crystal structure of parent molecule by MM energy minimization approach.