Chirality transfer upon preferential binding of homochiral guests to one stereoisomer of a conformationally equilibrated atropisomeric cyclophane is reported.

Herein, we report a water‐soluble macrocyclic host based on perylene bisimide (PBI) chromophores that recognizes natural aromatic alkaloids in aqueous media by intercalating them into its hydrophobic cavity. The host–guest binding properties of our newly designed receptor with several alkaloids were studied by UV/Vis and fluorescence titration experiments as the optical properties of the chromophoric host change significantly upon complexation of guests. Structural information on the host–guest complexes was obtained by 1D and 2D NMR spectroscopy and molecular modelling. Our studies reveal a structure–binding property relationship for a series of structurally diverse aromatic alkaloids with the new receptor and higher binding affinity for the class of harmala alkaloids. To our knowledge, this is the first example of a chromophoric macrocyclic host employed as a molecular probe for the recognition of aromatic alkaloids.

We have previously reported the formation of fluorescent 2,5-bis(arylethynyl)rhodacyclopentadienes from the reaction of [Rh(k 2-O,O-acac)(PMe 3) 2 ] (acac ¼ acetylacetonato) with a,u-bis(arylbutadiynyl)alkanes. However, a second isomer series, namely phosphorescent rhodium biphenyl complexes, was also obtained from the same reaction mixture, which made purification of the 2,5-bis(arylethynyl)rhodacyclopentadienes challenging and led to low isolated yields. Herein, we describe a synthetic protocol to access the desired fluorescent rhodium complexes by reaction of [Rh(k 2-O,O-acac)(P(p-tolyl 3) 2)] with a,u-bis(arylbutadiynyl)alkanes, which gives exclusively 2,5-bis(arylethynyl)rhodacyclopentadienes, and subsequent phosphine ligand exchange. The rhodacyclopentadienes bearing P(p-tolyl 3) ligands have been investigated and compared to their PMe 3 analogs with regard to their photophysical properties, showing that the aromatic phosphine ligands enhance non-radiative decay from the singlet excited state S 1 , while no phosphorescence from T 1 is observed despite the presence of the heavy rhodium atom. One of the P(p-tolyl 3) ligands can also be exchanged for an N-heterocyclic carbene (NHC), leading to unsymmetrically coordinated rhodacyclopentadienes. * Dedicated to Professor John Gladysz on the occasion of his 65th birthday.

Herein, we report aw ater-soluble macrocyclic host based on perylene bisimide (PBI) chromophores that recognizes natural aromatic alkaloids in aqueous media by intercalating them into its hydrophobic cavity.T he host-guest binding properties of our newly designed receptor with several alkaloids were studied by UV/Vis and fluorescence titration experiments as the optical properties of the chromophoric host change significantly upon complexation of guests.S tructural information on the host-guest complexes was obtained by 1D and 2D NMR spectroscopya nd molecular modelling.O ur studies reveal as tructure-binding property relationship for aseries of structurally diverse aromatic alkaloids with the new receptor and higher binding affinity for the class of harmala alkaloids.T oo ur knowledge,t his is the first example of ac hromophoric macrocyclic host employed as am olecular probe for the recognition of aromatic alkaloids.About fifty years ago,the discovery of cation complexation by macrocyclic crown ethers marked the beginning of the field of supramolecular chemistry. [1] Since then, encapsulation of abroad variety of organic substrates by macrocyclic hosts has been reported [2] and the research focus in this field has shifted towards water-soluble artificial receptors [3] owing to their promising pharmaceutical and medical applications. [4] In this regard, cyclodextrins and cucurbiturils as well as hydrophilic pillararenes and calixarenes evolved as universal hosts for the complexation of drugs,v itamins,f ragrances,a nd other desirable guest molecules. [5] Foro ther applications,h owever, for example,t he detection and analysis of biomolecules, selectivity towards aspecific analyte is required. [6] This holds in particular true for so-called molecular probes which, in addition to ah igh selectivity for the recognition of specific guest molecules,a re required to show as pecific response to the respective analyte such as ac hange in absorbance or fluorescence. [7] Towards this goal, among macrocyclic receptors the class of cyclophanes appears to be highly promising. By additionally employing p-p-a nd CÀH-p-interactions for guest encapsulation, cyclophanes are suitable hosts not only for biologically important aromatic molecules such as certain amino acids, [8] nucleotides, [7b, 9] and the neurotransmitters epinephrine or dopamine [10] but also for carbohydrates [11] in water.However,the design of cyclophanes,which possess larger cavities and are composed of dyes,r emains challenging. [7b,12] Fori nstance,o nly recently Stoddart and co-workers have accomplished the extension of their famous viologen-based cyclophanes ("blue box") [13] by additional phenyl units to achieve the encapsulation of larger p-systems such as tetracene or corannulene. [14] Likewise,o ur efforts to synthesize cyclophanes based on the large and strongly aggregating perylene bisimide (PBI) fluorophores [15] only recently succeeded in the complexation of avariety of polycyclic aromatic hydrocarbons (PAHs) in organic solvents. [16] Herein, we...