Electronic Transition Oscillator Strength and UV Stability of Nematogenic Cyanobiphenyls—Role of Alkyl Chains

Abstract

The electronic transitions in the ultraviolet (UV)/visible (VIS) range of nematogenic 4′-n-alkyl-4-cyanobiphenyl (nCB) with butyl (4CB) and hexyl (6CB) groups have been studied. The UV/VIS and circular dichroism (CD) spectra of nCB (n = 4, 6) molecules have been simulated using the TDDFT/B3LYP/6-31+G (d) method. Mulliken atomic charges for each molecule have been compared with Loewdin atomic charges to analyze the molecular charge distribution and phase stability. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies corresponding to the electronic transitions in the UV/VIS range have been reported. Excited states have been calculated via CI-singles (CIS) with semiempirical Hamiltonian ZINDO. Furthermore, two types of calculations have been performed for model systems containing single and double molecules of nCB. The dimer complexes during the different modes of molecular interactions have also been taken into consideration in order to investigate the most energetically stable configuration. These computations provide valuable information regarding the role and flexibility of end chains in a particular phase behavior and UV stability.