Synthesis, photocyclization, stacking, solvatochromic properties, and liquid crystalline behavior of Y-enynes

We have designed and synthesized a new class of cross-conjugated enediynes (so-called “Y-enyne”) to investigate their optical and photochemical properties.; The photochemical investigation of the naphthyl substituted Y-enyne reveals that upon its irradiation at 350 nm, in the presence/absence of oxygen, this Y-enyne undergoes electrocyclic ring closure to a substituted phenanthrene via a proposed allene intermediate. In non polar solvents, a [1,5] H-shift in the allene affords the photoproduct, while in methanol protonation/deuteration of the central allenic carbon occurs. Evidence for the proposed strained allene intermediate is presented. The photoreaction was followed by NMR and UV. The X-ray structure of the photoproduct is reported.; Additionally, the interest in crystal engineering and solid-state architecture to design and generate networks has grown recently. The introduction of fluorine atoms in the styrene moiety in Y-enyne has resulted in such networks. The X-ray structure of the perfluorophenyl substituted Y-enyne reveals a face-to-face stacking interaction between phenyl and perfluorophenyl groups. The formation of “ladders” and hexagonal channels along the aromatic rings and the different types of interactions that led to the high order stacking of this compound are discussed. The X-ray structure shows the unusual distorted conjugation of this chromophore.; Furthermore, an approach to develop fluorescent probes from Y-enynes is reported. Different substitution patterns in Y-enynes result in distinct solvatochromic behavior. The combination of methoxy and perfluoro substitution is essential to probe the emission of Y-enynes. β,β-Bis (3,4,5-trimethoxyphenylethynyl)pentafluorostyrene shows the largest shift (94 nm bathochromic upon changing solvent from cyclohexane to acetonitrile). Lippert-Mataga treatment yields a slope of −10,800 cm−1 corresponding to a dipole moment change of 9.6 D. The solvatochromic shift supports formation of an intramolecular charge transfer (ICT).; Finally, we introduce the liquid crystalline behavior of Y-enynes. The advantages of liquid crystalline Y-enynes are their high molar extinction coefficient and their fluorescence making them an attractive target for industrial application such as liquid crystal display devices (LCDs). The approach to induce a mesophase in Y-enynes is presented. Synthesis of the first generation of Y-enyne dendrimers with C₂ and C₃ symmetry is reported. The charge transfer complexes of the dendrimers with 2,4,7-trinitro-9-fluorenone (TNF) induced a discotic columnar liquid crystal phase in C₂/TNF complex and discotic nematic phase in C₃/TNF complex. C₂ and C₃ dendrimers are highly fluorescent in both the solid state and in solution.