Excited-state properties and the static nonlinear optical (NLO) susceptibilities of a series of organic and organometallic phenylacetylene dendrimers have been studied using the density functional theory (DFT). The calculated electronic absorption spectra of these phenylacetylene dendrimers exhibit the most intensive excitations in the low-lying region. Besides, the absorption spectra of the organometallic systems show a considerable redshift as compared with the organic analogues. The response calculations reveal that both the expansion of the organic conjugated structure and the introduction of the organometallic group can lead to the drastic increase of the molecular first and second hyperpolarizabilities, especially for the dendrimers including ruthenium, whose β and γ values are enlarged about 1-2 orders of magnitude. For the organic dendrimers and the organometallic one involving palladium, the charge transfers with π→π* character occurred with the conjugated configurations are predominant for the molecular first and second hyperpolarizabilities. And on the other hand, the extremely high hyperpolarizabilities of the organometallic systems including ruthenium originate mainly from the transitions from ruthenium d-orbitals to π* orbitals located at the conjugated structures. In addition, the charge transfers of π→π* from the C≡C adjacent to ruthenium to the conjugated structures make minor contributions to for their β and γ values.

Key words: Density Functional Theory, Organic Phenylacetylene Dendrimers, Organometallic Phenylacetylene Dendrimers, Excited-state Properties, Nonlinear Optical Properties