Structural, Vibrational, and Electronic Characteristics of Enyne Macrocycles as a Function of Ring Strain

Eisler, Sara; McDonald, Robert; Loppnow, and Glen R.; Tykwinski, Rik R.

doi:10.1021/ja000617g

Cited by 66 publications

(63 citation statements)

References 70 publications

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“…Overall, the inplane s*-orbitals contribute more significantly to the total delocalization energy than do the in-plane and out-of-plane p*-orbitals. This suggests that hyperconjugative effects through s-bonds play a larger role in stabilizing the g-DEE structure than pelectron interactions such as homoconjugation that have been suggested previously [34]. The remarkably large delocalization energies for D -A-type 18e supply evidence for enhanced D -A electronic interactions via the enediyne backbone, which is in accordance with the conclusions of the UV/VIS analysis (vide supra).…”

supporting

confidence: 88%

Donor/Acceptor Effects on the Linear and Nonlinear Optical Properties of Geminal Diethynylethenes (g‐DEEs)

Zhao¹,

Zhou²,

Slepkov³

et al. 2007

Helvetica Chimica Acta

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A series of geminal diethynylethenes (g-DEEs) with electron-donating and/or electron-accepting (D/A) groups were synthesized via a Pd-catalyzed cross-coupling sequence. The UV/VIS spectra for donor -acceptor (D -A) functionalized g-DEEs 5, 8, and 11 show distinctive absorption trends attributable to intramolecular charge-transfer (ICT). The bond-length-alternation (BLA) index for the cross-conjugated enediyne framework varies slightly with different terminal substituents as determined by density-functional theory (DFT) calculations and single-crystal X-ray analysis. Ultrafast third-order optical nonlinearities for the g-DEEs were measured by the differential optical Kerr effect (DOKE) technique and show that terminal donor -acceptor substitution of g-DEEs enhances molecular second hyperpolarizabilities (g) in comparison to donor or acceptor g-DEEs. A small increase in the twophoton-absorption cross-section (s (2) ) is observed in the series 9 -11 as a result of increased functionalization. The effects of donor/acceptor substitution on electron delocalization along the cross-conjugated enediyne structure are evaluated on the basis of natural-bond-orbital (NBO) analysis. Solid-state structures of the four derivatives 3b, 4b, 7 and 8 were characterized by single-crystal X-ray structural analysis and show an asymmetric unit cell for one derivative, D -A g-DEE 8.1. Introduction. -Conjugated molecules with highly delocalized and polarizable pelectron systems are prospects for third-order nonlinear optical (NLO) materials, and could form the basis for achieving ultrafast all-optical-based computing and telecommunications technology [1] [2]. To find ideal and applicable organic NLO materials, a large number of organic chromophores have been extensively explored, with many efforts focused on linearly conjugated aromatic and/or nonaromatic pconjugated systems [2 -5]. In assessing the suitability of an organic material for NLO purposes, its efficiency/transparency trade-off at a specific wavelength is an important factor to be considered, and maintaining transparency in the visible region of the spectrum is a significant challenge [6]. Many linearly p-conjugated chromophores tend to perform poorly in this respect, and the pursuit of alternative molecular designs has become more and more appealing and important. In particular, the use of cross-

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supporting

confidence: 88%

Donor/Acceptor Effects on the Linear and Nonlinear Optical Properties of Geminal Diethynylethenes (g‐DEEs)

Zhao¹,

Zhou²,

Slepkov³

et al. 2007

Helvetica Chimica Acta

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“…201,202 A desire to explore the effects of ring strain in crossconjugated macrocycles such as 209 (Scheme 68) led to the synthesis of cyclophanes 290a-e by Tykwinski and Eisler (Scheme 95). 73 Spectroscopic and X-ray crystallographic analyses outlined the resultant changes in the bond orders as ring strain was increased and showed that, for example, correlations between 13 C NMR shifts, solid-state bond angles, and Raman frequencies were all essentially linear. X-ray crystallography of the most highly strained system, 290a, showed alkyne angles as small as 155°, making it one of the most strained alkynyl systems characterized to date.…”

Section: Radialene Substructuresmentioning

confidence: 99%

Oligomeric and Polymeric Systems with a Cross-conjugated π-Framework

2006

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“…8 In the emission spectrum of 3 frozen in 2-methyltetrahydrofuran at 77 K ( ex = 260 nm), a broad phosphorescence peak at around 365 nm was clearly observed. This peak was positioned at a shorter wavelength compared to that of the previously studied germylene-ethynylene compounds (around 380 nm).…”

mentioning

confidence: 92%

“…Compound 2 was further treated with butyllithium and diphenylgermanium dichloride to complete the germapericyclyne synthesis. It is interesting that in this case, tetrakis(TMSethynyl)germa[4]pericyclyne 3 was the only pericyclyne product obtained, although previous synthesis of perphenyl germapericyclynes from monogermane units led to the non-selective formation of [4]-, [6]-, and [8]pericyclynes. 6a Probably, this is due to the relieved repulsion of the cis conformation of the cyclization precursor between the phenyl and TMS-ethynyl groups, compared to the previous phenylphenyl and isopropyl isopropyl repulsions.…”

mentioning

confidence: 97%

Synthesis and Characterization of Ethynylated Germa[4]pericyclyne

Tanimoto¹,

Nagao²,

Hosokawa³

et al. 2016

Chem. Lett.

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This paper presents the synthesis and characterization of (TMS-ethynyl)-substituted germa [4]pericyclyne composed of acetylene moieties and germanium atoms. Characterization was performed by X-ray crystallography, UVvis absorption, and photoluminescence spectroscopy. DFT calculations suggested interactions between the side chain alkynes and the ringforming acetylenes through germanium vertex atoms. Keywords: Element-blocks | Germanium | PericyclynesResearch on polyacetylene materials has attracted increasing attention with the growing importance of "element-blocks" (functional nano building blocks composed of heteroatoms) for advanced electronic and optical materials.1,2 Skipped polyynes ([R 2 XC¸C] n ) have received particular interest as a versatile "element-block" due to their easy modification and tunability of their characteristics by choosing appropriate linker atoms (X). Specifically, recent reports reveal that by using group 14 heteroatoms like silicon, with smaller ionization energies than those of carbon, one can achieve electron delocalization (although usually, the conjugation is interrupted at the alkyne units), resulting in effective enhancement of electric and optical properties.4 Therefore, skipped polyynes are potential candidates for preparing functional materials such as semiconductors, ceramic precursors, and hole-transporting materials. 5We have studied the synthesis and properties of both acyclic and cyclic germylene-ethynylene materials containing germanium (Scheme 1).6 Having a smaller ionization energy than silicon, germanium also forms stronger bonds to sp-carbon compared to tin. Additionally, cyclic skipped Ge-polyynes, called germa [N]pericyclynes, display characteristic emission properties compared to acyclic molecules, due to the fixed conformations and through-bond/through-space interactions. Therefore, element-block polymers composed of germapericyclynes, which are expected to impart functionality superior to that provided by monomeric pericyclyne units, are a promising platform for the fabrication of unique optical materials. Polymeric pericyclyne materials with linear, branched, dendric, and spirocyclic forms can be designed, with each pericyclyne unit connected via alkyne bridges. Thus, to enable electronic delocalization across the alkyne units, it is necessary for the vertex atoms to mediate conjugation between the alkyne spacers. The existence of alkynealkyne interactions through Ge atoms in pericyclyne ring systems has been suggested in our previous investigations.6 Thus, exo-ethynylated pericyclynes could be expected to show exoendo and exoexo alkynes interactions, and would be suitable candidate monomer units for polypericyclynes. However, their optical properties along with their molecular orbitals have not been studied yet. To explore the unique character of germa[N]pericyclynes as polymer precursors, we herein disclose the synthesis of an ethynylated germa[4]pericyclyne for preliminary research on poly(germapericyclynes), and provide a discussion of its properties.Star...

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Structural, Vibrational, and Electronic Characteristics of Enyne Macrocycles as a Function of Ring Strain

Cited by 66 publications

References 70 publications

Donor/Acceptor Effects on the Linear and Nonlinear Optical Properties of Geminal Diethynylethenes (g‐DEEs)

Donor/Acceptor Effects on the Linear and Nonlinear Optical Properties of Geminal Diethynylethenes (g‐DEEs)

Oligomeric and Polymeric Systems with a Cross-conjugated π-Framework

Synthesis and Characterization of Ethynylated Germa[4]pericyclyne

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