Synthesis and Fluorescence Spectra of Oxa[3.n]phenanthrenophanes

Fluorescent cyclophanes and their applications

With the serendipitous discovery of crown ethers by Pedersen more than half a century ago and the subsequent introduction of host-guest chemistry and supramolecular chemistry by Cram and Lehn, respectively, followed by the design and synthesis of wholly synthetic cyclophanes-in particular, fluorescent cyclophanes, having rich structural characteristics and functions-have been the focus of considerable research activity during the past few decades. Cyclophanes with remarkable emissive properties have been investigated continuously over the years and employed in numerous applications across the field of science and technology. In this Review, we feature the recent developments in the chemistry of fluorescent cyclophanes, along with their design and synthesis. Their host-guest chemistry and applications related to their structure and properties are highlighted.

New ferrocene-triazole derivatives for multisignaling detection of Cu2+ in aqueous medium and their antibacterial activity

Ferrocene-based naphthalene or quinoline receptors 1-4 linked by triazole were designed and synthesized. Their recognition properties of metal cations have been investigated systematically in aqueous environment. Upon addition 1 equiv. of Cu²⁺ ion, receptors 1 (C₂₃H₁₉FeN₃O) and 2 (C₂₂H₁₈FeN₄O) showed fluorescent turn-off, enhanced absorption and color variations. At the same time, receptor 1 also caused the perturbation of redox potential after addition 1 equiv. of Cu²⁺ ion. Therefore, receptors 1 and 2 behaved as naked-eye chemosensors and fluorescent probes for Cu²⁺ without interference by other ions and with low detection limit. In addition, receptor 1 could also be considered electrochemical sensor for Cu²⁺ having excellent sensitivity and selectivity. However, increasing the molecules flexibility resulted in the lower selectivity of ion recognition in the case of receptors 3 (C₂₄H₂₁FeN₃O) and 4 (C₂₃H₂₀FeN₄O). Furthermore, this series of compounds were nontoxicity and receptor 1 exhibited certain antibacterial activity.

A modular LHC built on the DNA three-way junction

A light-harvesting complex composed of a π-stacked multichromophoric array in a DNA three-way junction is described. The modular design allows for a ready exchange of non-covalently attached energy acceptors.

Binding motif of terminal alkynes on gold clusters

Gold clusters protected by terminal alkynes (1-octyne (OC-H), phenylacetylene (PA-H) and 9-ethynyl-phenanthrene (EPT-H)) were prepared by the ligand exchange of small (diameter <2 nm) Au clusters stabilized by polyvinylpyrrolidone. The bonding motif of these alkynes on Au clusters was investigated using various spectroscopic methods. FTIR and Raman spectroscopy revealed that terminal hydrogen is lost during the ligand exchange and that the C≡C bond of the alkynyl group is weakened upon attachment to the Au clusters. Acidification of the water phase after the ligand exchange indicated that the ligation of alkynyl groups to the Au clusters proceeds via deprotonation of the alkynes. A series of precisely defined Au clusters, Au34(PA)16, Au54(PA)26, Au30(EPT)13, Au35(EPT)18, and Au(41-43)(EPT)(21-23), were synthesized and characterized in detail to obtain further insight into the interfacial structures. Careful mass analysis confirmed the ligation of the alkynes in the dehydrogenated form. An upright configuration of the alkynes on Au clusters was suggested from the Au to alkyne ratios and photoluminescence from the excimer of the EPT ligands. EXAFS analysis implied that the alkynyl carbon is bound to bridged or hollow sites on the cluster surface.

Oligo(3,6-phenanthrene ethynylenes): synthesis, characterization, and photoluminescence

A series of highly fluorescent, oligo(3,6-phenanthrene ethynylenes) (F1-F7) were synthesized, and their photophysical behavior was systematically investigated. They emitted light with highly emissive quantum yields, up to 0.92. Emissive wavelengths of these compounds relied on the number of phenanthrene blocks existing in the oligomers. Red-shifted emissions were observed as the number of phenanthrenes increased. On the basis of theoretical calculations, helical structures could be formed for F4-F7, indicating that the excimer emissions might be observed for F4-F7 due to the intramolecular π-π stackings of phenanthrenes in the helical structures. However, excimer emissions were only observed for F5-F7 in dilute cyclohexane and for F6 and F7 in dilute methylene chloride, respectively. No excimer emission was observed for F4-F7 in dilute tetrahydrofuran due to the degree of solvation.

Photochemical oxidative cyclisation of stilbenes and stilbenoids--the Mallory-reaction

After Mallory described in 1964 the use of iodine as catalyst for the photochemical cyclisation of stilbenes, this reaction has proven its effectiveness in the synthesis of phenanthrenes, other PAHs and phenacenes with a surprisingly large selection of substituents. The "early age" of the reaction was reviewed by Mallory in 1984 in a huge chapter in the Organic Reactions series, but the development has continued. Alternative conditions accommodate more sensitive substituents, and isomers can be favoured by sacrificial substituents. Herein the further developments and applications of this reaction after 1984 are discussed and summarized.

Synthesis, Characterization, and Fluorescence Behavior of Twisted and Planar B2N2-Quaterphenyl Analogues

A series of planar and twisted heteroaromatic quaterphenyl analogues containing BN ring linkages has been synthesized using primarily difunctional Lewis acidic diborabiphenyl moieties as molecular cores. Crystal structure analyses indicated the presence of large twist angles between adjacent aromatic rings in 1 and 3, which were also observed to possess nonfluorescent behavior due to a lack of molecular rigidity and insufficient B=N character in the excited state. In contrast, the incorporation of one or two bridging ethylene groups between the adjacent rings (installed via an ethynyl cycloisomerization) was found to afford planar phenanthrene or pyrene moieties, which resulted in weak fluorescence behavior (Phi F = 0.02-0.16) for the n-Bu and Ph derivatives 5-12. Emission colors ranged from green (lambda em = 521 nm) to red (lambda em = 630 nm) and depended primarily on the conformation (2,2'- vs 4,4'-), the extent of chromophore conjugation (phenanthrene vs pyrene), and the type of exocyclic substituent present (n-Bu vs Ph). Communication between the two phenanthrene or pyrene moieties was observed in some cases, which was characterized by bathochromically shifted emission bands relative to that of monomeric phenanthrene or pyrene species. Unique excited-state dimer (excimer) fluorescence was observed for the 2,2'-isomer 8, which was characterized by broad, low-energy emission bands bathochromically shifted from that of the corresponding monomer.

Facile Synthesis, Fluorescence, and Photochromism of Novel Helical Pyrones and Chromenes

[reaction: see text] Aryl coumaryl ethylenes undergo oxidative photocyclization readily to yield helical pyrone-annulated condensed aromatics. The pyrones are conveniently converted to the corresponding photochromic diphenylpyrans/chromenes. Both pyrones and chromenes exhibit helicity-dependent fluorescence efficiency and persistence, respectively.