Structural study of tropane-3-spiro-4'-imidazol-5'-one

Tropane-3-spiro-4'-imidazol-5'-one has been synthesized and its crystal and molecular structures determined by X-ray diffraction, IR, Raman, ¹H-NMR and ¹³C-NMR methods. The tautomeric equilibrium between this structure and the corresponding conjugated form in different solvents is also studied from IR and UV data. The imidazoline ring, the spiranic C(3, 4'), the N(8) and the methyl C(9) atoms are situated in a plane. The piperidine ring adopts a distorted chair conformation in the crystalline form and in solution. The flattening of the C(1), C(2), C(3, 4'), C(4), C(5) part of the chair and the opposite puckering are noticeably large. In order to complete the results, some spectroscopic measurements have also been made for the tropane-3-spiro-4'-imidazol-5'-one hydrochloride.     

Mega three-photon absorption cross-section enhancement in pseudoisocyanine J-aggregates

Herein we report an extraordinary three-photon absorption cross-section (sigma'3) enhancement in J-aggregates supramolecular systems. The much higher value of sigma'3 in PIC J-aggregate (2.5 x 10(-71) cm6 s2 ph(-2)) compared to typical values obtained in organic molecules (10(-80) cm6 s2 ph(-2)) is attributed to the strong molecular transition dipole moment coupling in the supramolecular assembly. Three-photon absorption of PIC J-aggregates and monomer aqueous solutions were measured using the well known open aperture Z-scan technique pumping with a 25 ps pulse laser-OPG system at 1720 nm. This novel result opens new expectations for applications of supramolecular systems in bioimaging and medicine.     

Synthesis,structural and conformational study of 4-α-(or β)-p-chlorobenzoyloxy-1-azaadamantane hydrochloride

4-α-(or β)-p-Chlorobenzoyloxy-1-azaadamantane hydrochloride have been synthesized and studied by ¹H and ¹³C nmr spectroscopy, and the crystal structure of the α-epimer has been determined by X-ray diffraction. Each ring of the adamantane cage system is a nearly perfect chair, the substituted cyclohexane and piperidine rings, in endo and exo position respectively, having the biggest deviation. From the ¹H and ¹³C nmr data, several stereoelectronic effects have been deduced.     

Unveiling electronic transitions in three novel chiral azo-compounds using linear and nonlinear circular dichroism: a theoretical-experimental study

Herein, we report on the experimental and theoretically study of the linear absorption, electronic circular dichroism (ECD) spectra, as well as the two-photon absorption circular-linear dichroism measurements of three different chiral azo derivatives in dimethylsulfoxide solution. Using potential energy surfaces and frontier orbital analysis, we established the most stable conformation for each molecule and elucidated their different electronic transitions. Our theoretical calculations allowed us to unambiguously identify the spectral position of such transitions and correlate them with the spectral profiles observed in the two-photon absorption spectra. To further elucidate the characteristics of the main electronic transitions in terms of spectral shape and position, we carried out measurements of the polarization dependent two-photon absorption cross sections and determined the two-photon circular-linear dichroism spectra of these azo dyes.     

Circularly Polarized Luminescence from Simple Organic Molecules

This article aims to show the identity of “circularly polarized luminescent active simple organic molecules” as a new concept in organic chemistry due to the potential interest of these molecules, as availed by the exponentially growing number of research articles related to them. In particular, it describes and highlights the interest and difficulty in developing chiral simple (small and non‐aggregated) organic molecules able to emit left‐ or right‐circularly polarized light efficiently, the efforts realized up to now to reach this challenging objective, and the most significant milestones achieved to date. General guidelines for the preparation of these interesting molecules are also presented.     

Fluorescence emission of disperse Red 1 in solution at room temperature

In this article, we report the fluorescence emission of Disperse Red 1 in solution at room temperature and pumping at 532 nm with a 25 mW diode laser. We have measured its fluorescence quantum yield in methanol, ethylene glycol, glycerol, and phenol obtaining values as high as 10(-3) in the aliphatic alcohols. The excitation spectra of Disperse Red 1 in all four solvents as well as its excitation anisotropy in glycerol are presented. Applying a Gaussian decomposition method to the absorption spectra along with the support from the excitation spectra, the positions of the different transitions in this pseudo-stilbene azobenzene dye were determined. Solvatochromic and isomerization constraint effects are discussed. Calculations using density functional theory at TD-B3LYP/6-31G*//HF/6-31G* level were performed to interpret the experimental observations.