Double stranded polymeric ladderphanes with 16-π-electron antiaromatic metallocycle linkers

Abstract

Three double stranded polymeric ladderphanes with 16-π-electron antiaromatic metallocycle linkers are synthesised by ring opening metathesis polymerisation of the corresponding bisnorbornene monomers. Scanning tunnelling microscopic (STM) images indicate that these polymers can assemble nicely on a graphite surface to form a highly ordered pattern which has been observed in other ladderphanes with different kinds of aromatic linkers. Little change in (1)H NMR, absorption spectra and electrochemical oxidation potential between these polymers and the corresponding monomers suggest that there would be no interactions between adjacent antiaromatic linkers in these polymeric ladderphanes. Presumably, the distance between two antiaromatic rings in these ladderphanes (5-6 Å) is far too long in comparison with that between two rings in methylene-bridged antiaromatic superphanes (2.5 Å<), where stabilisation is predicted by theoretical calculations.

Excimer Formation in a Confined Space: Photophysics of Ladderphanes with Tetraarylethylene Linkers

“…The absorption spectrum of monomer 10 a is essentially the sum of the absorptions of tetraarylethylene 6 and aminobenzoate 8 c ( Figure 1). [25] Like other single-and double-stranded polynorbornenes, [7,[14][15][16]19] the absorption due to the aminobenzoate chromophores in ladderphane 2 a (l max = 314 nm) exhibited a hypsochromic shift in comparison with that of 10 a (l max = 320 nm, Figure 1), which may be due to release of strain from the norbornene moiety. [28] On excitation at 350 nm, no emission was observed from solutions of 10 a, 6, and 8 c in CH 2 Cl 2 (1.0 10 À5 to 1.0 10 À3 m).…”

“…[19] Since the linkers in 1 are connected to the polymeric backbones through a benzylic or an ester group, certain flexibilities might be expected. These experiments are carried out at ambient temperature, so that thermally induced mo-tions can take place to enable interactions between adjacent chromophores.…”

“…[14] However, when 16-p-electron antiaromatic metallacycles are employed as linkers in 1, the photophysical and electrochemical properties of 1 remain unchanged in comparison with those of the corresponding monomer. [19] Since the linkers in 1 are connected to the polymeric backbones through a benzylic or an ester group, certain flexibilities might be expected. These experiments are carried out at ambient temperature, so that thermally induced mo-tions can take place to enable interactions between adjacent chromophores.…”

End Group Modification of Polynorbornenes

“…We have previously established that, upon treatment with the first‐generation Grubbs catalyst 3 , norbornenes fused with N ‐arylpyrrolidine 4 afford the corresponding polynorbornenes 5a (Figure ) with isotactic stereochemistry and all double bonds in trans ‐configuration . Thus, when the ROMP was quenched with 2 , 5b with an allyl acetate end group was obtained in 85% yield.…”

“…Upon treatment with the first generation of Grubbs catalyst, norbornenes fused with N ‐arylpyrrolidene moiety undergo ROMP stereoselectively giving the corresponding 2D comb‐like polynorbornenes with isotactic stereochemistry and all double bonds in trans ‐configuration . These protocols have recently been used for the construction of a series of polynorbornene‐based double‐stranded ladderphanes 1 9 having a range of aromatic, antiaromatic, and 3D organic and organometallic linkers, L, with diverse structural variety. Significant interactions between aromatic linkers in these ladderphanes may take place as evidenced by fluorescence quenching, excimer formation, as well as Soret band splitting (in prophyrin‐containing ladderphanes).…”