Diarylethene, absorbance

State was attained. After UV-light irradiation, about 80% of the absorbance at 580 nm was recovered. The conversion of 80% from 2a to 2b was almost the same as that in the solution phase. The conversion of the film prepared from 2a solution was 40%, which is half of the conversion of the film prepared from a solution of the closed-ring form isomer. This difference in the maximum conversion to 2b is caused by the conformation of the open-ring form isomers. The isomer has two conformations, anti-parallel and parallel conformations. The former is photoactive whereas the latter is inactive, and half of the open-ring form isomers are in the inactive parallel conformations in solution. Half of 2a molecules in the film prepared from 2a solution are in the inactive parallel conformation. The conformational change is difficult in the amorphous film below Tg. In contrast, 2a in the bleached film prepared from the solution of 2b is in an anti-parallel conformation, and the maximum conversion to 2b at the photostationary state is about two times larger than that in the film prepared from 2a solution. A similar increase in the conversions in the film prepared from the closed-form isomer has been observed in amorphous diarylethenes, 3-10. It should be noted that heat treatment of the bleached 7a film at a temperature above Tg resulted in a decrease in the maximum conversion, which indicates that conformational change takes place at temperatures above Tg. 

Figure 3.58. Absorbance of diarylethene embedded in PMMA films as a function of the angle between the infrared irradiation and the probe beam polarizations. The infrared polarization is either parallel ( ) or perpendicular (A). The normalized absorbance is expressed by the ratio of (Abs — Abs )j(Absm ix — Abs ), where Afonin is the minimum absorbance and Abslu i , corresponds to the maximum absorbance. (From Ref. [223] with permission of Elsevier.)...

FIGURE 3.16 Dependence of the absorbance of PMMA films containing (left) diarylethene and (right) spiropyran on the angle, 4, between UV irradiation and probe beam polarizations. The normalized absorbance is defined as (Abs - Abs n)/(Abs - Abs ,, where Abs j and Abs , are the maximum and minimum absorbances, respectively. The H and signs stand for the directions parallel and perpendicular to the UV polarization, respectively. The markers are experimental data points, and the full and dashed lines are cos 4 theoretical fits. The analysis wavelengths are indicated. Note the apparent n/2 angle-shift between the UV and visible orientational distributions of the diarylethene chromophore. After reference 29, redravm by permission. 

Wang also prepared compound 45 in which two UPy units are connected with a photochromic dithienylethene unit [112]. It exists as a cyclic monomer at low concentrations and undergoes concentration-dependent ring-opening polymerization process (Fig. 1.13). To explore the potential applications of the supramolecular polymer, a small amount of mono-UPy-terminated fluorescent dye FI was added to a solution of 45 to end-cap the linear polymer and then the mixture was spin coated to fabricate a smooth mixed film. The closed form of the diarylethene can absorb... 

Miklailov et have employed TDDFT to design two-photon operated molecular switches built from the diarylethene photoswitching unit and a two-photon absorbing pendant substituent. Both the one- and two-pho-ton absorption spectra were simulated and analyzed in order to understand... 

---