2-Nitrotriptycene is 4 times as efficient as nitrobenzene for second harmonic generation in nonlinear optics. Molecular orbital calculations have been carried out to rationalize this result. A correlation has been established between the characteristics of the optical absorption peaks, the electron distribution of the frontier molecular orbitals, and the magnitude of the hyperpolarizability coefficients beta. The enhancement of the beta-value seems to be due to a large electron transfer (0.9 e(-)) in the interaromatic ring charge transfer. The difference in dipole moment between the excited state and the ground state is consequently unusually large (17 D). The rather small corresponding extinction coefficients, however, lead to a beta-value of about 10 +/- 3 x 10(-30) esu.