Published: February 21, 2011 r2011 American Chemical Society 1774 dx.doi.org/10.1021/jp107046r | J. Phys. Chem. A 2011, 115, 1774–1780 ARTICLE pubs.acs.org/JPCA Ab Initio Theory for Ultrafast Magnetic Local Spin Flip on the Newly Synthesized Homodinuclear Complex [Ni II 2 (L-N 4 Me 2 )(emb)] G. Lefkidis,* ,† C. Li, ‡ G. Pal, z M. Blug, § H. Kelm, § H.-J. Kr€ uger, § and W. H€ ubner † † Department of Physics and Research Center OPTIMAS, Kaiserslautern University of Technology, PO Box 3049, 67653 Kaiserslautern, Germany ‡ School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an 710072, China z Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany § Department of Chemistry, Kaiserslautern University of Technology, PO Box 3049, 67653 Kaiserslautern, Germany ABSTRACT: We present a fully ab initio calculation, the synthesis and the characterization of the homodinuclear [Ni 2 II (L-N 4 Me 2 )- (emb)] complex, which can act as a prototypic, realistic substance for ultrafast laser-induced spin dynamics. The new compound, which has been synthesized and characterized, consists of two magnetic centers with different spin properties and different local symmetries (distorted octahedral versus distorted square-planar) and exhibits strong spin localization. We calculate the vibrational and electronic spectra of the compound and predict a local spin-flip scenario. The very existence and the properties of the compound represent an important step toward ultrafast experimental spin dynamics in ligand-stabilized multicenter compounds and paves the path toward laser-induced magnetic logic on a single molecule. 1. INTRODUCTION Today’s computer technology is strongly oriented toward both portability and efficiency, which means smaller and, at the same time, faster devices. The conventional semiconductor- based electronics is reaching its physical limits, and therefore, its alternatives are becoming more and more appealing for technological applications. Molecular spintronics on the other hand seems capable of overcoming some of the disadvantages of conventional transistors because it can combine a much higher information density (1 spin per about 100 atoms versus 1 elemen- tary charge per 10 4 atoms) with ultrafast dynamics. The latter has become obvious through the experimental evidence of laser-driven ultrafast magnetic manipulation in (anti)ferromagnetic materials 1-3 and motivates the search for materials which allow for spin manipulation both spectroscopically and spatially resolved, that is, both spin switch and spin transfer. The key idea is that while one (magnetic) center allows only for switch, two or more (magnetic) centers can additionally allow for spin transport and, with proper laser-induced dynamics, build (magnetic) logic elements. Thus, several interesting alternatives have seen the light of day in the recent years, starting from mesoscopical magnetoresistive elements, 4 magnetic-domain-wall logic, 5 and majority logic gates for magnetic quantum dots, 6 going over to the microscopical “moleculators”, capable of performing logic operations based on the environmental cation concentration as input. 7 All of these approaches being either top-down or bottom-up concentrate on speed or size but not both. It was already theoretically shown that nanoclusters with more than one magnetic center can perform the desired logic opera- tions by using the spin state on several magnetic atoms and an external magnetic field as input bits and, after a laser pulse, the magnetic state of a different atom as the output bit. 8 Key in- gredients are the spin localization, the possibility of local spin-flip and intramolecular spin transfer, and, of course, connection to an experimentally accessible quantity, for example, IR frequency markers (CO ligand). 9 This quantity can become spatially sen- sitive to the spin via symmetry breaking and proper resonant structures and hence map the localized magnetic states of the molecule to optical, IR, or UV absorption spectra. It is largely accepted that the interplay between light and matter proceeds through relativistic terms of the Hamiltonian and the light- induced polarization in the material. 3,10,11 Received: July 28, 2010 Revised: January 14, 2011