Effects of interaction between the chelate rings and π‐conjugated systems in fused salphen complexes on UV‐Vis‐NIR spectra

Dinuclear (Zn₂, Ni₂, and NiZn) complexes of fused salphen with acene‐type annelation were synthesized from 3,7‐diformyl‐2,6‐dihydroxynaphthalene. The spectroscopic properties of these complexes were compared with those of their constitutional isomers with phene‐type annelation. The acene‐type complexes exhibited a characteristic absorption band in the near‐infrared region that showed a noticeable solvent effect. Time‐dependent density functional theory calculations suggested that the absorption arose from a π → π* transition localized at the naphthalene ring, which was perturbed by the adjoining chelate rings. Effects of the connection topology in the fused salphen complexes are discussed by comparison with those of polycyclic aromatic hydrocarbons.     

Disordered loop model and coupled conformal field theories

A family of models for fluctuating loops in a two-dimensional random background is analyzed. The models are formulated as O(n) spin models with quenched inhomogeneous interactions. Using the replica method, the models are mapped to the M→0 limits of M-layered O(n) models coupled each other via _1,3 primary fields. The renormalization group flow is calculated in the vicinity of the decoupled critical point, by an epsilon expansion around the Ising point (n=1), varying n as a continuous parameter. The one-loop beta function suggests the existence of a strongly coupled phase (0<n<n_*) near the self-avoiding walk point (n=0) and a line of infrared fixed points (n_*<n<1) near the Ising point. For the fixed points, the effective central charges are calculated. The scaling dimensions of the energy operator and the spin operator are obtained up to two-loop order. The relation to the random-bond q-state Potts model is briefly discussed.     

Halogen-substituent effect on the spectroscopic properties of 2-phenyl-6-dimethylaminobenzothiazoles

6-Dimethylamino-2-phenylbenzothiazole (1-H) is a push-pull benzothiazole fluorophore mimicking the firefly oxyluciferin structure. We newly prepared 7-chloro and 7-bromo derivatives of 1-H and its 4-acetyl derivative (2-H), and their spectroscopic and photophysical properties were investigated. The halogenated derivatives showed the blue-shifted electronic absorption maxima and fluorescence emission maxima compared to 1-H and 2-H, resulted from the deformations of the NMe₂ groups and the electron withdrawing properties of the halogen groups. In addition, the halogen substitutions accelerate intersystem crossing by heavy atom effect, resulting in a decrease in fluorescence quantum yields. Interestingly, however, the halogenated derivatives of 2-H still showed moderate fluorescence quantum yields. The halogenation effect is one of the guides to design push-pull benzothiazole fluorophores for tuning fluorescence properties.     

Quantum control of a chiral molecular motor driven by laser pulses

"Molecular motors or machines" are one of the hot subjects in chemistry because they play an important role in molecular devices. We have theoretically demonstrated that unidirectional rotations of a chiral molecular motor can be driven by using tailored linearly polarized laser pulses. The findings obtained here serve as a theoretical basis for control of functions such as gearing or acceleration of molecular motors.     

Fluorescence enhancement of bis-acridine orange peptide, BAO, upon binding to double stranded DNA

Bis-acridine orange peptides carrying two acridine oranges at the epsilon-amino moieties of both terminal lysines of a tetra(lysine) chain showed a ca. 200-fold fluorescence enhancement upon addition of double stranded DNA.     

An electric cyclophane: cavity control based on the rotation of a paraphenylene by redox switching

Although a free rotation around a single bond gives no mechanical output, it has let us imagine a molecular motor. A para-substituted aromatic ring can be regarded as a rotator with the para-rotation axis. When it is incorporated in a wider pi-conjugated system, a quinoidal structure is generated accompanied by oxidation on the substituted groups at the 1,4-position, and the axis is fixed. A paraphenylenediamine was selected as the nanomechanical molecular module capable of locking and releasing the free rotation using an electrode in solution. We inserted the module into a simple molecular system, cyclophane. It was clarified that the cyclophane was able to open and close its cavity in a reversible redox process repeatedly.     

Single-crystal-to-single-crystal transformation of diolefin derivatives in nanocrystals

Topochemical [2 + 2] cycloaddition polymerization of methyl p-phenylenediacrylate and 2,5-distyrylpyridine in nanocrystals, prepared by the reprecipitation method, were investigated in comparison with those in bulk crystals. The bulk single crystals, larger than 1 mum in size, broke into microcrystals with variety of size and shape in the course of polymerization. Interestingly, however, these nanocrystals show single-crystal-to-single-crystal transformation.     

Description of molecular dynamics in intense laser fields by the time-dependent adiabatic state approach: application to simultaneous two-bond dissociation of CO2 and its control

We theoretically investigated the dynamics of structural deformations of CO(2) and its cations in near-infrared intense laser fields (approximately 10(15) W cm(-2)) by using the time-dependent adiabatic state approach. To obtain "field-following" adiabatic potentials for nuclear dynamics, the electronic Hamiltonian including the interaction with the instantaneous laser electric field is diagonalized by the multiconfiguration self-consistent-field molecular orbital method. In the CO(2) and CO(2+) stages, ionization occurs before the field intensity becomes high enough to deform the molecule. In the CO(2)(2+) stage, simultaneous symmetric two-bond stretching occurs as well as one-bond stretching. Two-bond stretching is induced by an intense field in the lowest time-dependent adiabatic state |1> of CO(2)(2+), and this two-bond stretching is followed by the occurrence of a large-amplitude bending motion mainly in the second-lowest adiabatic state |2> nonadiabatically created at large internuclear distances by the field from |1>. It is concluded that the experimentally observed stretched and bent structure of CO(2)(3+) just before Coulomb explosions originates from the structural deformation of CO(2)(2+). We also show in this report that the concept of "optical-cycle-averaged potential" is useful for designing schemes to control molecular (reaction) dynamics, such as dissociation dynamics of CO(2), in intense fields. The present approach is simple but has wide applicability for analysis and prediction of electronic and nuclear dynamics of polyatomic molecules in intense laser fields.     

Adjustment of twist angles in pseudo-helical lanthanide complexes by the size of metal ions

Control of self-assembled nanostructures is a promising technique for nanotechnology. We have examined as to whether nanostructures could be controlled by the size of the central metal ion. Lanthanides are a natural choice for such a study as the size of their trivalent ions changes with atomic number gradually. For this investigation, a series of rare earth complexes ([LaL(1)], [CeL(1)], [SmL(1)], [TbL(1)], [YL(1)], and [LuL(1)]) with a tripodal heptadentate ligand L(1) were synthesized, and their X-ray crystallographic analysis was performed. Although the structures of the ligand (H(3)L(1)) and of the metal complex ([ML(1)]) were quite different, all complexes were almost isostructural pseudohelices. The result of the crystallographic studies demonstrated that the twist angles of helices in the complexes depend on the ionic size of the central metal. A detailed analysis helped determine which portion of the helical strand contributed to the total helicity, and the major cause for the difference in helicity among the lanthanides is discussed. Moreover, this result is the first example showing that La(I) (II) and Lu(I) (II) complexes with the same tripodal heptadentate ligand are isostractural.     

Calculations of ionization and excitation energies for SiH3 X (X = F,Cl, Br and I) using the discrete variational Xα method

The electronic structure of silyl halide SiH₃ X molecules are investigated using the discrete variational Xα method based on the Hartree—Fock—Slater model. Theoretical ionization and excitation energies are in very good agreement with the experimental results of UPS and UV spectra. The effects of Si 3d orbitals are found to be significant on the bondings and orbital energies.