Versatile Bottom‐up Approach to Stapled π‐Conjugated Helical Scaffolds: Synthesis and Chiroptical Properties of Cyclic o‐Phenylene Ethynylene Oligomers

Abstract

Spring loaded: the smallest members of a family of carbon nanocoils (CNCs), adopting a fixed helical structure, have been synthesized by introduction of one or two staples in o-phenylene ethynylene oligomers. The chiroptical responses of the systems having enantiopure L-tartrate-derived staples confirmed the induced helicity. Theoretical studies suggest that these CNCs are pseudoelastic.

Helicene Monomers and Dimers: Chiral Chromophores Featuring Strong Circularly Polarized Luminescence

“…We note however,t hat the magnitude of CPL could possibly be influenced by the number of acetylene moieties per molar mass in am olecule whicha ppearst o coincidew ith other CPL data reported for polycyclic aromatic hydrocarbons bearing multiple acetylene units. [24] Future research will hopefully help confirming why the all-carbon-backbone chromophores, dimeric( P) 2 -1 and monomeric (P)-8 and (P)-9,d isplayC PL intensities of such largem agnitude as observed in our measurements (Figure 5a nd Figure S7 in the Supporting Information).…”

“…The g lum values in all CPL spectra are very large, reaching j 0.025 j for monomeric (P)-and( M)-8 (black in Figure5), whichi ss ubstantial compared to most previously reportedv alues for helicenes and for pure organic molecules in general. [10,12,23,24] The dimericc arbohelicenes (P) 2 -a nd (M) 2 -1 and monomeric (P)-and (M)-9 ( Figure S7 in the Supporting Information) [13] also reach values of j 0.02 j .T hiene-2,5-diyl linked dimerich elicenes (P) 2 -a nd (M) 2 -2 (dark blue in Figure5)o rp yrrole-2,5-diyll inked (P) 2 -a nd (M) 2 -3 (green in Figure 5) displayed valuesi nt he range of g lum % j 0.01 j .T he substituents at the C- Table 1. Optical and chiropticalp roperties of the new dimers (P) 2 -3-7 in comparison to the data for the previouslyp ublishedd imers (P) 2 -1 and 2 and monomers (P)-8 and 9.S hown are the intensities (e)o ft he 1 B b and 1 B a absorptionb ands, [19] the absorptiona nisotropy factors g abs (= De/e)a t % 430 nm, the fluorescence emissionb ands (l em ), the absolute fluorescence quantum yields measured by integrating sphere (F f ), [20] andt he CPL factor j g lum j = 2 DI/I (I = intensity of circularly polarized light).…”

Circularly Polarized Luminescence Switching in Small Organic Molecules

“…In compound 13,t he OPE can be fixed into ah elical conformation. [44] The introductiono fe nantiopure 2,3-dihydroxybutane diethers allows for the chirality transfer to OPE and thus chiral helical conformation. The theoretical calculations (B3LYP/6-31G*) suggested P helical configuration was favored energetically by about 2kcal mol À1 with respectt ot he M helical configuration in the case of S,S configured diols, whichw as also approved by the CD results.…”

Sulfoxide‐Induced Homochiral Folding of ortho‐Phenylene Ethynylenes (o‐OPEs) by Silver(I) Templating: Structure and Chiroptical Properties

“…[21] We recently showedt hat folded o-OPE-based nanopores could be filled with silver(I)c ations through carbophilic interactions with alkynes, [22] to give an ew class of metallofoldamers (Figure 1, acyclica chiral organic emitters). [23] We also synthesized helical stapled o-OPEs [24] with an enantiopure 2,3-dihydroxybutane diether moiety,w hich showed excellentC PL responses ( Figure 1, cyclic chiral enantiopure organic emitters). [25] These homochiral helically folded structures suffer from a change in the CPL emission in the presenceo fsilver(I);thus exemplifying the first case of CPL-active, small,organic,molecular emitters, the response of which can be modulated by carbophilic interactions in ar eversible manner.T hese results showed the potential of OPEs as efficient andv ersatile CPL emitters.…”