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Use of Mixed-Valence Complexes as Nonlinear Optical Chromophores

IP.com Disclosure Number: IPCOM000111560D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Moylan, CR: AUTHOR

Abstract

Many organic compounds have been synthesized for nonlinear optical applications such as frequency doubling and electro-optic modulation. To be useful for such applications, a compound must have a large molecular hyperpolarizability &beta. and a large dipole moment &mu.. The hyperpolarizability is proportional to the oscillator strength of the lowest-energy electronic transition, the difference in dipole moment between the ground and excited states, and the square of the wavelength corresponding to the absorption maximum. Since the usable component of the molecular hyperpolarizability tensor is that which lies along the molecular dipole moment, the ideal chromophore has an intramolecular electron transfer transition that takes place colinear with the molecular dipole, and has a very strong oscillator strength.

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Use of Mixed-Valence Complexes as Nonlinear Optical Chromophores

      Many organic compounds have been synthesized for nonlinear
optical applications such as frequency doubling and electro-optic
modulation.  To be useful for such applications, a compound must have
a large molecular hyperpolarizability &beta.  and a large dipole
moment &mu..  The hyperpolarizability is proportional to the
oscillator strength of the lowest-energy electronic transition, the
difference in dipole moment between the ground and excited states,
and the square of the wavelength corresponding to the absorption
maximum.  Since the usable component of the molecular
hyperpolarizability tensor is that which lies along the molecular
dipole moment, the ideal chromophore has an intramolecular electron
transfer transition that takes place colinear with the molecular
dipole, and has a very strong oscillator strength.  Most compounds
prepared for nonlinear optical studies are linear, delocalized
structures, such as stilbenes, with an electron donor added at one
end and an electron acceptor at the other end.  The amount of charge
transfer taking place in the excited state is less than a full
electron, but it can take place over large distances so that the
change in dipole moment upon excitation is respectable.

      Mixed-valence complexes are a completely different type of
compound in which a full electron can be transferred between two
metal centers, colinear with the dipole moment.  These inorganic
species were first prepared by Taube and coworkers [1], and have been
the subject of intense research ever since [2].  These coordination
compounds have the following general formula:

      (L&sub1.)[x]M&sub1.(+n)L[b] M&sub2.(+(n+1))(L&sub2.)[y]
where M&sub1.  and M&sub2.  are metal ions whose oxidation states
differ by one electron, L&sub1.  and L&sub2.  are ligands associated
with one metal or the other, and L[b]  is a bridging ligand
connecting the two metals.

      Mixed-valence complexes are expected to have large ground-state
dipole moments,...