The surprising nonlinear optical properties of conjugated polyyne oligomers

Abstract

Polyynes represent a unique class of conjugated organic compounds. The third-order nonlinear optical response of polyynes has been extensively modeled theoretically, and it is generally believed that the increase in molecular second hyperpolarizability (gamma) as a function of length for polyynes should be lower than that for polyenes. Experimental evidence to test this prediction, however, has been absent. We have synthesized conjugated polyynes that contain up to 20 consecutive sp-hybridized carbons, and we have determined their nonresonant gamma-values as a function of the number of acetylene repeat units (n). These gamma-values demonstrate a power-law behavior versus n(gamma approximately n(4.28+/-0.13)), with an exponent that is both larger than theoretically predicted for polyynes and substantially higher than that observed for polyenes or polyenynes. Furthermore, no saturation of the linear or nonlinear optical properties is observed.

Carbon-atom wires: 1-D systems with tunable properties

“…18). 123,124 This power law behaviour was stronger than that theoretically predicted for polyynes, and it was higher than that reported for polyenes and polyenynes. The second method evaluated the NLO behaviour based on the vibrational contribution to the second hyperpolarizability (γ vib ) for adamantyl endcapped CAWs (Ad[n]), using the quantitative Raman spectra and the Raman scattering intensities that correspond to the polyyne.…”

Molecular Weight Effects in the Third-Harmonic Generation Spectroscopy of Thin Films of the Conjugated Polymer MEH-PPV

“…Short chains such as conjugated oligomers show a significant increase in the wavelength of the maximum of the main absorption band (λ max ) and the second hyperpolarizability (γ) per repeat unit, which usually follow power law dependencies of the chain length in a regime up to approximately 2 nm. 10,11,18,51 For chain lengths larger than typically 2 nm, socalled saturation effects are observed, which means that λ max and γ per repeat unit converge to finite values that are sensitively dependent on the chemical structure and conformation of the polymer. [52][53][54][55][56][57][58][59][60] However, it was noted recently that the twophoton absorption coefficient of thin films of a polydiacetylene can still increase with M w , even if M w is significantly larger than the saturation limit of γ per repeat unit.…”

sp Carbon chain interaction with silver nanoparticles probed by Surface Enhanced Raman Scattering

“…sp carbon has been produced by means of different physical and chemical techniques [10][11][12][13][14][15][16][17] and has been also observed in the core of multiwalled carbon nanotubes [18,19]. Interesting transport properties have been predicted and measured [20,21] and a strong non-linear optical response of finite linear carbon chains has been recently measured [22].…”