An effective Hamiltonian in a basis of spin-and space-symmetry adapted configuration state functions ͑CSF͒, which includes information from Kohn-Sham density functional theory ͑DFT͒, is used to calculate configuration interaction ͑CI͒ wave functions for the electronic states of molecules. The method emphasizes on states of multiconfigurational character which cannot be represented by conventional DFT. The CI matrix elements are constructed empirically by using the exact operator and corrections from DFT. Both the optimized KS orbitals from the parent determinant and the corresponding KS potential from the parent state density are used. Depending on their energy gap the CI off-diagonal elements between CSF are exponentially scaled to zero to avoid double counting of electron correlation. The selection of the most important CSF describing nondynamical correlation effects and the use of an approximate resolution of the identity ͑RI͒ for the evaluation of the two-electron integrals allows a very efficient DFT/MRCI treatment of molecules with several hundreds of electrons. As applications, the prediction of excitation energies for singlet and triplet states of organic molecules and transition metal complexes, the calculation of electronic circular dichroism spectra and investigations of the energetics of diradicals are presented. It is found, that the new DFT/MRCI approach gives results of high accuracy ͑rms errors for relative energies Ͻ0.2 eV͒ comparable to those from sophisticated ab initio treatments.

We present a parallelized version of a direct selecting multireference configuration interaction (MRCI) code [S. Grimme and M. Waletzke, J. Chem. Phys. 111, 5645 (1999)]. The program can be run either in ab initio mode or as semiempirical procedure combined with density functional theory (DFT/MRCI). We have investigated the efficiency of the parallelization in case studies on carotenoids and porphyrins. The performance is found to depend heavily on the cluster architecture. While the speed-up on the older Intel Netburst technology is close to linear for up to 12-16 processes, our results indicate that it is not favorable to use all cores of modern Intel Dual Core or Quad Core processors simultaneously for memory intensive tasks. Due to saturation of the memory bandwidth, we recommend to run less demanding tasks on the latter architectures in parallel to two (Dual Core) or four (Quad Core) MRCI processes per node. The DFT/MRCI branch has been employed to study the low-lying singlet and triplet states of mini-n-beta-carotenes (n=3, 5, 7, 9) and beta-carotene (n=11) at the geometries of the ground state, the first excited triplet state, and the optically bright singlet state. The order of states depends heavily on the conjugation length and the nuclear geometry. The (1)B(u) (+) state constitutes the S(1) state in the vertical absorption spectrum of mini-3-beta-carotene but switches order with the 2 (1)A(g) (-) state upon excited state relaxation. In the longer carotenes, near degeneracy or even root flipping between the (1)B(u) (+) and (1)B(u) (-) states is observed whereas the 3 (1)A(g) (-) state is found to remain energetically above the optically bright (1)B(u) (+) state at all nuclear geometries investigated here. The DFT/MRCI method is seen to underestimate the absolute excitation energies of the longer mini-beta-carotenes but the energy gaps between the excited states are reproduced well. In addition to singlet data, triplet-triplet absorption energies are presented. For beta-carotene, where these transition energies are known from experiment, excellent agreement with our calculations is observed.

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Combined methods of cyclophane and bipyridine synthesis open the way to the new planar-chiral 2,2'-bipyridine 1, whose CD spectrum is strongly dependent on metal salts. The absolute configuration of the chiral precursor 2 could be assigned by comparison of experimental and theoretical CD spectra. The usefulness of planar chirality in heterocyclic transition metal ligands is revealed in experiments towards stereoselective catalysis using 1.Chiral ligands are the key compounds in asymmetric catalysis. 2 A ligand playing a major role in transition metal complexation is 2,2'-bipyridine, which has been frequently provided with stereogenic centres. Chiral bipyridines are not only used in asymmetric synthesis, 3 but also for the organization of stereochemically defined supramolecular 4 structures. 5 We combined intramolecularly two structural features that have always been important in stereochemistry as well as in coordination chemistry, the [2.2]paracyclophane system and the 2,2'-bipyridine complex ligand, resulting in a planar chiral ligand of a new type, 13-pyridinyl [2](1,4)benzeno[2](2,5)pyridinophane (1).The number of planar chiral ligands based on ferrocenes in catalytic asymmetric synthesis is very high. 6 A [2.2]paracyclophane skeleton, however, has rarely been described so far in this field. 7 We now make use of the special attributes of the [2.2]paracyclophane type scaffold as chiral unit. It possesses a high sterical demand that is particularly effective because of its rigidity. Furthermore, the chiral information is located near to the metal ion, one side being shielded by the benzene ring.To obtain the key educt for 1, the [2](1,4)benzeno[2](2,5)pyridinophane (2), which is once mentioned in literature, but, concerning synthesis and precursors, was insufficiently described, 8 we proceeded from commercially available 2,5-pyridinedicarboxylic acid, which was converted into the diethyl ester via the acid chloride.The diol 3, generated by reduction of the ester through sodium borohydride/calcium chloride in ethanol, 9,10 could be isolated exclusively by using a strongly acidic cation exchange resin (e.g. Amberlite IR 200 C) 11 . After bromination of the diol, 12 we obtained the dibromide 4. Under high-dilution conditions 13 and by taking advantage of the cesium effect, 14 4 was coupled with 1,4-bis(sulfanylmethyl)benzene to yield 2,11-dithia [3](1,4)benzeno[3](2,5)pyridinophane 5.Irradiation of 5 with ultraviolet light (Hg, 180 W) in a thiophilic solvent generated the [2.2]phane 2, the N-oxide Reagents and conditions: i, SOCl 2 , reflux, 8 h, recryst. of acid chloride (petroleum ether 40/60), then EtOH, reflux, 2 h, 82%; ii, NaBH 4 (2 equiv), CaCl 2 (1 equiv), EtOH, r.t., 16 h, 67%; iii, HBr/HOAc (30%), r.t., 6d; iv, sol. A: 4 in EtOH, sol. B: 1,4-bis(sulfanylmethyl)benzene (1 equiv), KOt-Bu (2.3 equiv) in EtOH (85%); Cs 2 CO 3 in mixture, reflux, 16 h, 62%; v, P(OMe) 3 , hν (Hg, 180 W), r.t., 18 h, 84%; vi, MCPBA (2 equiv), CH 2 Cl 2 , r.t., 20h, then N,Ndimethylcarbamoyl chloride (1.3 equiv.), TMSCN (1.3 equ...

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