Investigating the potential of organic semiconductor materials by DFT and TD-DFT calculations on aNDTs

The effects of substituting electron withdrawing and electron donating functional groups on the electronic and optical properties of angular naphthodithiophene (aNDT) were studied. Substitutions were made to the aNDT molecule at position 2 and 7, respectively. The computed ionization parameters and reorganisation energies distinguished between the p-type and n-type semiconducting natures of the unsubstituted aNDT molecule and those with the –C(2)H(5), –OCH(3), –NO(2), and –CN substituents. However, the aNDT molecule with C(2)H(5) as a substitution showed p-type behaviour since it had the largest electron reorganisation energy of about 0.37 eV. The ambipolar semiconducting property of methoxy [–OCH(3)–] substituted aNDT molecule was revealed from the RMSD value of 0.03 Å for both positive and negative charges with respect to neutral geometry. The absorption spectra differ significantly from those of unsubstituted aNDT, which reveals the impact of functional group substitution that changes the energy level of the molecules. The maximum absorption (λ(max)) and oscillator strength (f) at the excited states in vacuum was investigated using time dependent density functional theory (TD-DFT). The aNDT with electron withdrawing group [-NO(2)] substitution has a maximum absorption wavelength of 408 nm. Studying the intermolecular interactions between aNDT molecules was also accomplished with the help of Hirshfeld surface analysis. The current work provides insight into the development of novel organic semiconductors.