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Absolute Raman intensity measurements and determination of the vibrational second hyperpolarizability of adamantyl endcapped polyynes
Author(s) -
Lucotti A.,
Tommasini M.,
Fazzi D.,
Del Zoppo M.,
Chalifoux W. A.,
Tykwinski R. R.,
Zerbi G.
Publication year - 2012
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.3166
Subject(s) - hyperpolarizability , raman scattering , raman spectroscopy , chemistry , conjugated system , molecule , nonlinear optics , computational chemistry , analytical chemistry (journal) , organic chemistry , optics , physics , polarizability , polymer , laser
Linear sp‐carbon polyynes are ideal molecules for the direct investigation of the physical properties of one‐dimensional conjugated systems. Traditionally, the main obstacle to the study of these systems has been their instability under normal laboratory conditions. Thanks to improved chemical syntheses, a broadened range of polyynes is now available for study, including the hydrocarbon series endcapped with adamantyl groups, Ad[ n ]. In this work, the quantitative Raman spectroscopic analysis is reported for each member of this homologous series. The Raman scattering intensities corresponding to the major features of the polyyne segment (i.e., the effective conjugation coordinate or Я lines) are then used to evaluate the nonlinear optical (NLO) behavior via determination of the vibrational contribution to the second hyperpolarizability ( γ vib ). This study shows that γ vib values as a function of length are of the same order of magnitude as those arising from the electronic contribution to the molecular second hyperpolarizability, γ ele , as reported for triisopropylsilyl polyynes, TIPS[ n ], using the differential optical Kerr effect technique. The nonlinear response for Ad[ n ] polyynes, supported by the analogous response for TIPS[ n ] polyynes, confirms that linear sp‐carbon molecules have large second hyperpolarizabilities that show a power‐law increase in γ ‐values versus length that is larger than other known π‐conjugated systems, such as polyenes. Furthermore, the NLO response of polyynes versus length approaches the theoretical limit described by Kuzyk more closely than other conjugated organic oligomers. Copyright © 2012 John Wiley & Sons, Ltd.