# Sunlight Bleaching of Subporphyrazine Dye Films
## 4 Conclusions  
(a) The degree of bleaching of SubPz/SubPc thin films exposed to sunlight strongly depends on the environment. While it was intuitively anticipated that the light-driven reactions would run differently in ambient air and in inert gas, the substrate effect was unsuspected. (b) The impact of air can be dammed by varying the composition of peripheral rings in a subphthalocyanine molecule. Parent SubPc5\({}_{0}\)H\({}_{12}\) subphthalocyanine discolors deeply in air but is more stable in argon, whereas for SubPz5\({}_{3}\)H\({}_{0}\), the situation is reversed. These observations are valid for films deposited on bare glass. (c) ITO coating on glass generally inhibits photobleaching. The exception is a SubPz5\({}_{3}\)H\({}_{0}\) film irradiated in the presence of oxygen, in which the Q-band intensity drops nearly 10-fold, i.e., the films become almost transparent. By further replacing the substrates with PET/ITO and glass/FTO, we confirmed that namely ITO components are responsible for this anomaly. Presumably, the accelerated bleaching of SubPz5\({}_{3}\)H\({}_{0}\) films on ITO results from a specific reaction of symmetrical subporphyrazine macroligand in its photoexcited state with O\({}_{2}\) in the presence of (catalyzed by?) indium-containing species coming from the conductive coating. (d) If near-UV photons are removed from the incident light by application of a long-pass filter cutting \(\lambda<\) 400 nm, then the spectrum of irradiated films changes only slightly. A slight change after UV-free irradiation is basically due to the solid-state processes, such as annealing-induced morphological transformation. In addition, some photoactivated reactions with residual atmospheric components and/or with admixtures emerging from the substrate cannot be ruled out. (e) Therefore, photo(catalytic?) destruction of the subphthalocyanine chromophore is effective only when high-energy electronic transitions in the dye molecule corresponding to the Soret-band range are involved. This finding can potentially be useful in the design or selection of phthalocyanine-based materials for thin-film electronic devices, where photostability is an important issue. For instance, the macroheterocycles having blue-shifted Soret-band would be interesting in photovoltaics, since the destructive UV component of sunlight will naturally be filtered by the substrate through which the light enters the device. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app13021211/s1](https://www.mdpi.com/article/10.3390/app13021211/s1)]([https://www.mdpi.com/article/10.3390/app13021211/s1](https://www.mdpi.com/article/10.3390/app13021211/s1)): Figure S1. Initial sections of the 'temperature vs. time' dependence: (**a**) light-On and (**b**) light-Off (direct sunlight). Rsqr--correlation coefficient; Figure S2. Cross-sectional profiles and 3D surface maps of V-metallized SubPz5\({}_{3}\)H\({}_{0}\) films on glass, scanning area 0.3 \(\times\) 0.3 mm\({}^{2}\): pristine film (**a**) and films irradiated by the direct sunlight in Ar (**b**), filtered sunlight in Ar (**c**), and filtered sunlight in air (**d**); Figure S3. Height distribution (top panels) and 2D images (bottom panels) of V-metallized SubPz5\({}_{3}\)H\({}_{0}\) films on glass: pristine film (**a**) and films irradiated by the direct sunlight in Ar (**b**), filtered sunlight in Ar (**c**), and filtered sunlight in air (**d**); Figure S4. (**a**) Absorption spectrum of the SubPz5\({}_{3}\)H\({}_{0}\) film in the UV/Vis/NIR range and transmission of the glass/ITO substrate (red dashed line). (**b**) Absorption spectrum of the SubPz5\({}_{3}\)H\({}_{0}\) film from Figure 4a and transmission of the GS-12 optical filter in the visible/NIR range. Filter cuts off the wavelengths <400 nm, while in the area of Q-band, its transparency is better than 90%. The AM1.5 G simulated sunlight has a shortwave limit at \(\sim\)300 nm; Figure S5.