Intramolecular charge transfer with the planarized 4-aminobenzonitrile 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6)

Fast and efficient intramolecular charge transfer (ICT) and dual fluorescence is observed with the planarized aminobenzonitrile 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6) in a series of solvents from n-hexane to acetonitrile and methanol. Such a reaction does not take place for the related molecules with 1-isopropyl (NIC6) and 1-methyl (NMC6) groups, nor with the 1-alkyl-5-cyanoindolines with methyl (NMC5), isopropyl (NIC5), or tert-butyl (NTC5) substituents. For these molecules, a single fluorescence band from a locally excited (LE) state is found. The charge transfer reaction of NTC6 is favored by its relatively small energy gap DeltaE(S(1),S(2)), in accordance with the PICT model for ICT in aminobenzonitriles. For the ICT state of NTC6, a dipole moment of around 19 D is obtained from solvatochromic measurements, similar to micro(e)(ICT) = 17 D of 4-(dimethylamino)benzonitrile (DMABN). For NMC5, NIC5, NTC5, NMC6, and NIC6, a dipole moment of around 10 D is determined by solvatochromic analysis, the same as that of the LE state of DMABN. For NTC6 in diethyl ether at -70 degrees C, the forward ICT rate constant (1.3 x 10(11) s(-1)) is much smaller than that of the back reaction (5.9 x 10(9) s(-1)), showing that the equilibrium is on the ICT side. The results presented here make clear that ICT can very well take place with a planarized molecule such as NTC6, when DeltaE(S(1),S(2)) is sufficiently small, indicating that a perpendicular twist of the amino group relative to the rest of the molecule is not necessary for reaching an ICT state with a large dipole moment. The six-membered alicyclic ring in NMC6, for example, prevents ICT by increasing DeltaE(S(1),S(2)) relative to that of DMABN.     

Finite element investigation of the ground states of the helium trimers 4He3 and 4He2–3He

A three‐dimensional finite element method is applied to the ground states of the symmetric and asymmetric atomic helium trimers ⁴He₃ and ⁴He₂–³He. Three different He–He interaction potentials of hard‐core nature were studied. Two extrapolation procedures based on the convergence properties of the finite element method are investigated. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

The dynamics of second-order equations with delayed feedback and a large coefficient of delayed control

The dynamics of second-order equations with nonlinear delayed feedback and a large coefficient of a delayed equation is investigated using asymptotic methods. Based on special methods of quasi-normal forms, a new construction is elaborated for obtaining the main terms of asymptotic expansions of asymptotic residual solutions. It is shown that the dynamical properties of the above equations are determined mostly by the behavior of the solutions of some special families of parabolic boundary value problems. A comparative analysis of the dynamics of equations with the delayed feedback of three types is carried out.     

BINOL-derived diphosphoramidites bearing unsymmetrical 1,2-diamine link and their application in asymmetric catalysis

New P,P-bidentate diastereomeric diphosphoramidite chiral ligands with mixed stereogenic elements and a C₁ backbone symmetry have been prepared from (S_a)- and (R_a)-1,1′-binaphthyl-2,2′-diol (BINOL) and (S)-N-benzyl-1-(pyrrolidin-2-yl)methanamine and are fully characterized. The use of these ligands provides up to 84% ee in the Pd-catalyzed asymmetric allylic substitution of (E)-1,3-diphenylallyl acetate and up to 95% ee in the Rh-catalyzed asymmetric hydrogenation of α-dehydrocarboxylic acid esters. The results indicate that the catalytic performance is highly affected by the axial chirality of the binaphthyl moieties of the ligand and the nature of the solvent.