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

Abstract

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 "dark" to "light" conformational transition occurs between the two isomers. This hypothesis was confirmed by anisotropy decay measurements.

Synthesis and Properties of 6-Aryl-4-azidocinnolines and 6-Aryl-4-(1,2,3-1H-triazol-1-yl)cinnolines

“…Among azidoheterocycles, azidoquinolines (Figure 2A) [17,18,19,20,21,22,23] and azidopyridazines (Figure 2B) [24,25,26,27,28] are well known, however only one known example of an azidocinnloline has been reported to date (Figure 2C) [29], while triazolylcinnolines still remain unknown. Taking into account that the cinnoline core can be found both in biologically active compounds with different types of activities [30,31,32,33,34] and in fluorescent materials [35,36,37,38,39,40], the development of a synthetic route towards azidocinnolines and triazolylcinnolines could lead to new biologically active molecules and interesting fluorescent probes.…”

27 Years of Catalytic Carbonylative Coupling Reactions in Hungary (1994–2021)

“…Moreover, carbonylative syntheses applied on a cavitand skeletons were not mentioned in the literature at all, with the exception of the works of our research group. In the recent ten years, our research group had developed several palladium-and copper-catalyzed reactions on a cavitand sceleton [86][87][88][89], including palladium-catalyzed aminocarbonylation [90][91][92][93].…”

Synthesis of Novel Cavitand Host Molecules via Palladium-Catalyzed Aryloxy- and Azidocarbonylation

“…In the last decade, our research group had developed and described several palladium- and copper-catalyzed homogeneous catalytic processes on a cavitand scaffold, including the palladium-catalyzed aminocarbonylation [ 13 ], copper-catalyzed azide-alkyne cycloaddition (CuAAC) [ 14 , 15 ] and Sonogashira or Suzuki-Miyaura coupling [ 16 ]. It has been proven that homogeneous catalytic processes can be easily adopted for cavitands, and similar results can be expected in terms of both reactivity and selectivity as in the case of small molecules.…”