Shpolskii matrix

A Shpolskii (or Shpol'skii) matrix is a low-temperature host-guest system consisting of guest or impurity chromophore embedded in a crystaline matrix. The fluorescence emission spectra and absorption spectra of Shpolskii matrices exhibit narrow lines instead of the inhomogeneously broadened features normally associated with spectra of chromophores in liquids or solids. The phenomena was first described by Éduard Vladimirovich Shpol'skiĭ in the 1950s [E. V. Shpolskii, A. A. Ilina and L. A. Klimova, 1952, Transactions Doklady of the U.S.S.R. Academy of Sciences, volume 87, pages 935] and 1960's [E. V. Shpolskii, 1960, Line Fluorescence Spectra of Organic Compounds and Their Applications. Soviet Physics Uspekhi, volume 3, pages 522-531 [http://dx.doi.org/10.1070/PU1960v003n03ABEH003277 DOI Link] ] [E. V. Shpolskii, year 1962, Problems of the Origen and Structure of the Quasilinear Spectra of Organic Compounds at Low Temperatures, Soviet Physics Uspekhi,volume 5,pages 522-531 [http://dx.doi.org/10.1070/PU1962v005n03ABEH003436 DOI Link] ] [E. V. Shpolskii, 1963, New Data on the Nature of the Quasilinear Spectra of Organic Compounds, Soviet Physics Uspekhi, volume 6, pages = 411-427 [http://dx.doi.org/10.1070/PU1960v003n03ABEH003277 DOI Link] ] in the journals "Transactions of the U.S.S.R. Academy of Sciences" and "Soviet Physics Uspekhi".

Shpolskii matrices are formed when each chromophore neatly replaces one or more molecules in the host crystaline lattice. A good match between the chromophore and the host lattice leads to a uniform environment for all the chromophores and hence greatly reduces the inhomogeneous broadening of the electronic transitions. In addition to the weak inhomogeneous broadening of the transitions, the quasi-lines observed at very low tempeatures are phonon-less transitions. [J. L. Richards and S. A. Rice, 1971, Study of Impurity-Host Coupling in Shpolskii Matrices, Journal of Chemical Physics, volume 54, pages = 2014-2023 [http://dx.doi.org/10.1063/1.1675132 DOI Link] ] Since phonons originate in the lattice, an additional requirement is weak chromophore-lattice coupling. Weak coupling increases the probability of phonon-less transitions and hence favors the narrow zero phonon lines. [J. Friedrich and D. Haarer, 1984, Photochemical Hole Burning - a Spectroscopic Study of Relaxation Processes in Polymers and Glasses, Angewandte Chemie-International Edition in English, volume 23, pages = 113-140 [http://dx.doi.org/10.1002/anie.198401131 DOI Link] ] The weak coupling is usually expressed in terms of the Debye-Waller factor, where a maximum value of one indicates no coupling between the chromophore and the lattice phonons. The narrow lines characteristic of the Shpolskii matrix are only observed at cryogenic temperatures because at higher temperatures many phonons are active in the lattice and all of the amplitude of the transition shifts to the broad phonon sideband. The original observation was made at liquid nitrogen temperature (77 kelvins), but using temperatures close to that of liquid helium (4.2 K) yields much sharper spectral lines and is the usual practice.

Shpolskii matrices result from fortuitous compatibility between the chromophore and the host matrix and most of the known systems consist of dilute solutions of mono- or polycyclic aromatic hydrocarbons in low molecular weight linear alkanes. The solution is often flash frozen with cold helium gas. Linear alkanes interact weakly with the chromophores and crystallize when frozen. The length of the alkanes is often chosen to approximately match the dimensions of the chromophore, and are usually in the size range between n-pentane and n-dodecane.

ee also

*Zero-phonon line and phonon sideband
*Phonon

Notes

Journal links may require subscription (DOI-Digital object identifier).

References

# cite journal
author = J. Friedrich and D. Haarer.
year = 1984
title = Photochemical Hole Burning - a Spectroscopic Study of Relaxation Processes in Polymers and Glasses
journal = Angewandte Chemie-International Edition in English
volume = 23
pages = 113–140
doi = 10.1002/anie.198401131 [http://dx.doi.org/10.1002/anie.198401131 DOI Link]
# cite journal
author = V. Gebhardt, K. Orth and J. Friedrich.
year = 1996
title = Optical spectroscopy and ground state dynamics of methyl groups
journal = Journal of Chemical Physics
volume = 104
pages = 942–949
doi = 10.1063/1.470817 [http://dx.doi.org/10.1063/1.470817 DOI Link]

External links

* [http://www.physics.montana.edu/faculty/rebane/Research/Tutorials/Hole_burning/HoleBurning_00.htm Aleksander Rebane's site at Montana State University, Bozeman ]
* [http://hyperphysics.phy-astr.gsu.edu/hbase/molecule/molspecon.html#c1 Hyperphysics: Molecular Spectra]