Nonlinear Optical Response of Tetrel-Modified Tetraphenyl-Adamantane Clusters.

The second harmonic generation (SHG) properties of adamantane-based tetraphenyl clusters are predicted from first principles and analyzed on the basis of the involved electronic transitions. In particular, the effect of a tetrel substitution in the cluster core on the nonlinear optical response is investigated. Electronic transitions spatially localized at the substituents are found to be responsible for the optical nonlinearities. The intensity of the SHG signal grows with the atomic number of the considered tetrel. As the substitution does not distort the cluster core or substantially alter its symmetry, the enhanced SHG intensity is traced to a higher electron density at the substituents. The latter results in a larger spatial overlap of the states involved in the electronic transitions, which increases their probability. The presented results provide a theoretical foundation for the design of tailored nonlinear optical sources.