Page 111 - Photoreactive Organic Thin Films

ZOUHEIR SEKKAT

0.15 -

I
-e o.io -

0.05

0.00
400 500 600
(A)
Wavelength (nm)

60x10

500
Wavelength (nm)
FIGURE 3.15 UV-vis absorption spectra of PMMA films containing (A) diarylethene and (B)
spiropyran before (I) and after (2,3) linearly polarized UV irradiation.The probe light was also linearly
polarized, and spectra were obtained for both parallel, Abs//, and perpendicular, Abs x, orientations. The
insets in (A) are expanded views of both the UV and the visible absorptions of the diarylethene
chromophore. Identical spectra were obtained for both Abs// and Abs^ before UV irradiation. For both
the diarylethene and spiropyran chromophores, inasmuch as the orientational hole burning and
orientational redistribution processes occur with Absj_ > Abs// within the irradiation wavelength band,
note the inversion of the sign of the dichroism between the UV and visible bands of the spectra. After
reference 29, redrawn by permission.

measurements were performed with a probe light polarized either parallel or
perpendicular to the initial irradiating light polarization. The probe beam
was propagating perpendicular to the plane of the sample and linearly
polarized at 45 degrees with respect to the plane of incidence of the
irradiating beam. The transmitted parallel and perpendicular components