Photo-Orientation Dynamics and Transitions Symmetry

Real-time dichroism experiments were used to investigate the dynamics of photo-orientation of SP and DE in films of PMMA. The samples were irradiated with linearly polarized light while in situ transmittance 

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., orientations. The insets in (A) are e q anded 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 Abs 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. 

V (d rees), between Pump and Probe Polarizations 

FIGUitE 3.17 Real-time evolution of the isotropic absorbance (left) and the anisotropy (right) of Spin PMMA upon linearly polarized UV irradiation for several irradiation intensities.The numbers from I to 5 indicate the value of the irradiation intensity in units of Einstein.s. cm with the coiresponding sample absorbance (value in parentheses) at the irradiation wavelength (365 nm). The moments of turning the irradiation light on and off are indicated. After reference 26, redrawn by permission. 

and Pjicos mlH) = 0.642. wlfl = 71.25 and - 29.24 degrees are the angles, calculated using Equation 3,2, between the B isomer s transition moments at 365 and 633, and 546 and 633 nm, respectively, = 11380 and - 3460 L moHcm were adapted from the literature,and the fastest component of the thermal isomerization rate, k = 0.00125 s used in Equation 3,20 for the determination of 

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