# Sunlight Bleaching of Subporphyrazine Dye Films
## 3 Results and Discussion
### Photobleaching
#### 3.4.2 On Transparent Conductive Oxides (Glass/ITO, PET/ITO, Glass/FTO)
This might be explained by the partial \"dissolving\" of intact dye molecules in the end-products of the destruction reaction. Next, we examined the photodestruction in the SubPzS\({}_{3}\)H\({}_{0}\) films deposited on PET/ITO substrates, where the bulk support under the conductive indium tin oxide coating is polymeric--Figure 6. Here, the Q-band was composed of five subbands (Figure S13). The fifth component arose at the longwave shoulder at around 613 nm, similar to what was observed in the SubPzS\({}_{3}\)H\({}_{0}\) films on glass/ITO irradiated in air. This new subband tended to grow in the samples exposed to sunlight. The photobleaching of SubPzS\({}_{3}\)H\({}_{0}\) films on PET/ITO was even more severe than in the case of a glass/ITO substrate--Figure 6a. The D\({}^{Q}\)\({}_{\text{pristine}}\)/D\({}^{Q}\)\({}_{\text{irradiated}}\) ratio was 12.2 and 3.0 for the films irradiated in air and in argon, respectively--cf. Table 3. We tentatively assume that the release of indium-containing species from the conductive layer made on the porous and flexible organic support could proceed more easily. The diffusion of chemically active organic admixtures from the PET substrate through a thick ITO coating towards the subporphyrazine layer is less realistic. The following experiment was carried out to clear up the effect of indium-containing species. SubPzS\({}_{3}\)H\({}_{0}\) was dissolved in dehydrated high-purity acetone with and without a pre-added equimolar (10\({}^{-5}\) M) quantity of indium acetylacetonate, In(Acac)\({}_{3}\), in a 10 mm quartz cuvette. As known, In(Acac)\({}_{3}\) can serve as a precursor for the fabrication of ITO by the CVD process [32]. In this way, we attempted to imitate, very roughly, of course, a reaction between the indium ion and the dye molecule. The spectra of the mixed SubPzS\({}_{3}\)H\({}_{0}\):In(Acac)\({}_{3}\) solution were recorded as a function of time in the dark and under illumination within 6 h under continuous argon purging. Photobleaching of the irradiated SubPzS\({}_{3}\)H\({}_{0}\) solution with the indium content occured 15% faster than in the control sample without In(Acac)\({}_{3}\). Furthermore, three low-intensity bands clearly appeared in the range of 620-760 nm in place of the initial blurry arc, and their intensity grew with the irradiation time--Figure 6b. These bands may indicate the reduction/tetrarization processes associated with the formation of trace amounts of indium tetrakis(thiadiazole)porphyrinazine or phthalocyanine complexes (Figure S7c) [33]. In the case of a SubPzS\({}_{3}\)H\({}_{12}\):In(Acac)\({}_{3}\) solution prepared and treated in similar conditions, the intensity of the Q-band did not differ for solutions with or without indium. In this case, there appeared only one low-intensity band at 650 nm (Figure S7c). Chemical reactions withophthalocyanine and its derivatives usually proceed through cleavage of the halogen axial ligand due to high lability of the B-Cl bond [4, 34] (Figure S7). From theoretical considerations [4], the farther the electron density is shifted from the heterocycle to the periphery, the lower the B-Cl bond energy is. Therefore, the detachment of chlorine in the axial position will proceed easier in SubPcS\({}_{3}\)H\({}_{0}\) than in SubPcS\({}_{0}\)H\({}_{12}\). Experiments with solutions help visualize intermediates or colored reaction products that cannot be registered in thin-films samples due to (i) a very small amount of the reagent (In) and (ii) a growing absorption tail in the long-wavelength region for samples on a glass/ITO substrate--cf. Figure 5b. Note that the degree of photobleaching of SubPc/SubPz was practically independent of whether it occured in atmospheric (i.e., relatively humid) or synthetic (dry) air--Table 3, Figure 5. Therefore, the destruction reaction involves oxygen, being less sensitive to other ambient air components.