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Proceedings Paper

Nonlinear optical properties of bacteriorhodopsin: assignment of the third-order polarizability based on two-photon absorption spectroscopy
Author(s): Robert R. Birge; M. B. Masthay; Jeffrey A. Stuart; Jack R. Tallent; Chian-Fan Zhang
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Paper Abstract

The third-order (pi) -electron polarizability, (gamma) (pi), of bacteriorhodopsin in the 0.0 - 1.2 eV optical region is assigned based on an analysis of the experimental two-photon properties of the low-lying singlet state manifold. The following selected values of (gamma) (pi) (units of 10-36 esu) are observed: (gamma) (0;0,0,0) equals 2482 +/- 327; (gamma) (-3(omega) ;(omega) ,(omega) ,(omega) ) equals 2976 +/- 385 ((omega) equals 0.25 eV), 5867 +/- 704 ((omega) = 0.5 eV), 14863 +/- 1614 ((omega) = 0.66 eV), 15817 +/- 2314 ((omega) equals 1.0 eV), 10755 +/- 1733 ((omega) equals 1.17 eV). The third-order polarizability of this protein which contains an all-trans retinyl protonated Schiff base chromophore with six double bonds, is comparable to that observed for much longer chain polyenes (for example, dodecapreno (beta) -carotene, a polyene with 19 double bonds, exhibits a third-order (pi) -electron polarizability at 0.66 eV of 17000 +/- 6000 X 10-36 esu. The authors attribute the enhanced third-order nonlinearity associated with the protein bound chromophore of bacteriorhodopsin to two mutually enhancing origins. First, the chromophore is protonated, and the resultant charge reorganization enhances the polarizability in a fashion that is similar to that known to occur for polaronic and bipolaronic chromophores. It is estimated that protonation generates a five-fold enhancement in (gamma) (pi). Second, the protein bound chromophore exhibits a large change in dipole moment upon excitation into the lowest-lying, strongly-allowed 1B*u+-like state ((Delta) (mu) = 13.5 D). The latter property is responsible for a Type III enhancement of the third-order polarizability, and yields at least a 20-fold increase in (gamma) (pi).

Paper Details

Date Published: 1 June 1991
PDF: 12 pages
Proc. SPIE 1432, Biomolecular Spectroscopy II, (1 June 1991); doi: 10.1117/12.44213
Show Author Affiliations
Robert R. Birge, Syracuse Univ. (United States)
M. B. Masthay, Syracuse Univ. (United States)
Jeffrey A. Stuart, Syracuse Univ. (United States)
Jack R. Tallent, Syracuse Univ. (United States)
Chian-Fan Zhang, Syracuse Univ. (United States)

Published in SPIE Proceedings Vol. 1432:
Biomolecular Spectroscopy II
Robert R. Birge; Laurence A. Nafie, Editor(s)

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