Electronic spectra, and the nonlinear optical (NLO) properties of five isomers of C-96 were investigated using density functional theory and semi-empirical methods. The simulated electronic spectra of C-2:181, C-1:144, C-1:145, and C-2:176 have strong absorptions above 500 nm. The electronic spectra of C-1:144, C-1:145, and C-2:176 are similar. The third-order NLO properties of the isomers were analyzed under an external field. Small structural differences between C-1:144 and C-1:145 result in NLO responses that occur at different external fields. Entropy effects on the NLO properties are significant. The NLO responses of the five most stable isomers differ in the concentration averaged sample. (C) 2015 Elsevier B.V. All rights reserved.