Intramolecular Cooperative Effects in Multichromophoric Cavitands Exhibiting Nonlinear Optical Properties

We report on the design, synthesis, and characterization of a new class of multichromophoric cavitands based on resorcin[4]arenes. The novel compounds have exhibited high values of second-order nonlinear optical (NLO) properties, as evidenced by electric-field-induced second harmonic generation (EFISHG) measurements. Theoretical calculations indicate the presence of edge-to-face T-shaped interactions between the aromatic building blocks within these multichromophoric systems, which is further supported by the detection of hypsochromic shifts in UV-vis and upfield aromatic chemical shifts in 1H NMR. We proved for the first time that the gain in the quadratic hyperpolarizabilities of multichromophoric NLO macrocycles, originating from the near parallel orientations of the subchromophores, can be partially suppressed if the distance between the dipolar subunits falls into a specific range, where intramolecular cooperative and/or collective effects are operative. Our finding will contribute to the better understanding of the phenomenon of cooperativity in new molecular materials with promising NLO properties. (Figure Presented). © 2015 American Chemical Society

Syntheses and characterization of novel ruthenium complexes based on 1,3-dicyanobenzene

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Light-Enhanced Fluorescence of Multi-Level Cavitands Possessing Pyridazine Upper rim

Completely different fluorescence behaviour of cavitands based on a same calix[4]resorcinarene compound was observed. While the fluorescence intensity of the parent compound, tetramethyl-cavitand (1) slowly faded as a result of UV-light exposure, the emission of the three level cavitand with pyridazine moieties at the upper rim (5a) was enhanced by the excitation in the UV-region. The structure of fluorescence emission (characterized by excitation-emission matrices) and the absorption of 5a remained unaltered. The analysis of fluorescence decay curves reveals the presence of two separated components assigned to two individual emitting species. The measured significant increase of the average lifetime and quantum yield is the consequence of the UV-light induced transition between the different states of 5a. These observations can be explained by the structural difference between 5a and 1. As a counterpart of the naked cavitand (1) with methyl substituents at the upper rim only, 5a has three additional moieties benzene, triazole and pyridazine levels. Computational studies proved the existence of two conformational isomers of 5a. Upon ultraviolet light excitation a Bdark^ to Blight^ conformational transition occurs between the two isomers. This hypothesis was confirmed by anisotropy decay measurements

The Use of Calixarenes in Metal-Based Catalysis

The condensation of formaldehyde with p-alkylphenols under alkaline conditions, a reaction dating back to the days of Baeyer and Zinke, affords initially linear polyphenols, which, once a certain temperature is achieved, yield cyclic oligomeric phenolic compounds (Scheme 1). One-step, multigram synthetic procedures have now been developed, which by varying either the temperature or amount of base used in the preparation, readily afford the tetrameric, hexameric, and octameric phenolic ring systems, bridged by methylene (-CH2-) spacers. Ring systems with up to 20 phenolic residues are now known, although methods of preparation for these higher members, and for those with an odd number of phenolic residues, are usually low yielding. The smaller members of the family adopt a cone-shaped structure, hence the name calix[n]arene coined by Gutsche, from the Greek “calix” meaning vase, where n denotes the number of phenolic residues. Such a bowl shape results in the formation of a hydrophobic, electron-rich cavity, which is well-suited to the formation of inclusion complexes, particularly cations.5 The synthetic methodology has also been adapted to allow for the incorporation of bridging groups other than methylene, such as dimethyleneoxa (-CH2OCH2-), thia (-S-), and aza [-CH2N(R)CH2-] bridged calixarenes,6 and these additional donors can provide extra binding sites