Molecular Rotor based on an Oxidized Resorcinarene

Molecular single stator-double rotor activity of an oxidized resorcinarene (fuchsonarene) macrocycle containing unsaturated hemiquinonoid groups at its meso positions was investigated. Fuchsonarenes containing two hemiquinonoid substituents at diagonally-opposed meso-positions with two electron rich phenol groups at the remaining meso-positions between the hemiquinonoid groups. All meso-substituents are in proximity at one side of the resorcinarene macrocycle (so-called rccc-type isomer) with rotational activity of the phenol meso-substituents. Rotation rates of the phenol moieties can be controlled by varying temperature, solvent polarity and acidity of the medium of study with rotation being thermally activated in neutral and acidic media and tunable in the range from 2 s-1 to 20,000 s-1. Experimental and computational data indicate that rotation of the mobile phenol meso-substituents is remotely affected by interactions with acidic solvents at the carbonyl C=O groups of macrocyclic acetyloxy groups, which occurs with the emergence of a lower energy electronic absorption band whose intensity is correlated with both the acidity of the medium and the rotation rate of the phenol substituents. Time-dependent DFT calculations suggest that the low energy band is due to a molecular conformational adjustment affecting electronic conjugation caused by strong interaction of macrocyclic acetyloxy carbonyl groups with the acid medium. The work presents a molecular mechanical model for estimating solution acidity and also gives insight into a possible method for modulating rotor activity in molecular machines.

Multicolor-Raman analysis of Korean paintworks: emission-like Raman collection efficiency

It has been reported that the scattering cross-sections of resonance Raman spectra strongly depend on the resonance between the laser's excitation energy and the electronic absorption band of pigments in solution.

Intermolecular Interactions in Water-Ethanol Mixtures, Studied by Ultrasound Technique

Containing -OH groups with non-participant electrons, water and primary alcohols, form clusters by hydrogen bonds. Mixtures of water and ethanol and their ternary solutions containing small amounts of a spectrally active substance were studied by ultrasound techniques in order to determine the coefficient of adiabatic compressibility considered as being an indicator of the strength of intermolecular interactions in hydroxy liquids. A linear dependence between the adiabatic compressibility of solution and the wavenumber in the maximum of the solute electronic absorption band was evidenced in our experiments.

Two-Photon Absorbing Organic Chromophores for Optical Limiting

Strong optical limiting and large two-photon absorptivities are reported for a class of bisdonor diphenylpolyene derivatives with varying polyene bridge lengths. These molecules exhibit strong optical limiting using nanosecond pulses over a broad spectral range. Bis(diphenylamino)stilbene exhibits a 90 nm red shift of its optical limiting band, and only a minimal shift of about 13 nm of its lowest one-photon electronic absorption band relative to bis(di-n-butylamino)stilbene. This suggests a potential for broadband optical limiting with high transparency using mixtures of such compounds. Pulse width dependent nonlinear transmission measurements suggest that two-photon pumped excited-state absorption contributes significantly to the limiting of nanosecond pulses.

The 0.9 eV Absorption Band of Polyaniline: A Morphologically Sensitive Electronic Absorption

The optical absorption spectra of polyaniline in the visible and UV spectral regions have been characterized before. The electrically conductive form has a band gap absorption at 3.8 eV and polaron absorptions at 2.9 and 1.5 eV [1,2] . An additional electronic absorption band at 0.9 eV was found to be also related to the existence of polaron. The assignment of this transition has yet to be made. Epstein and co-workers [31 have found a photo-induced absorption band at 0.9 eV by photo-exciting emeraldine base (insulator) with 2.0 eV light. It is not known yet whether these two 0.9 eV transitions belong to the same set of electronic energy levels of polaron, or they belong to two different electronic systems but are coincidentally have the same transition energy.