# Sunlight Bleaching of Subporphyrazine Dye Films
## 1 Introduction  
Subphthalocyanines and subporphyrazines (SubPc and SubPz) are tripyrrole-type dyes with tunable optical and redox properties that make them suitable candidates for use as nonfullerene acceptors in molecular electronics devices. In solutions, the interaction of molecules with the visible light has been studied quite well, including study on the photoexcited states, and their relaxation pathways [1; 2; 3]. In solids, however, the situation becomes intricate due to the intermolecular interactions, optical screening, or crystal-size effects.  
[PERSON] et al. [4] investigated the electronic structure of boron subphthalocyanine halide molecules using the density functional theory, DFT. They found that the nature of the axial ligand governs the stability of the macrocycle, while peripheral substituents rather affect the electrical and optical properties of the material. [PERSON] et al. [5] examined the oxygen-dependent photophysics and photochemistry of subphthalocyanine derivatives and found out that the photosensitized production of a singlet molecular oxygen, O\({}_{2}\)(a\({}^{1}\)A\({}_{\beta}\)), by these molecules is a key step in the degradation process. Furthermore, the addition of either \(\beta\)-carotene or aastaxanthin as antioxidants inhibited degradation due to a combination of three processes. The first is deactivation of O\({}_{2}\)(a\({}^{1}\)A\({}_{\beta}\)) to the oxygen ground state, O\({}_{2}\)(X\({}^{3}\)E\({}^{-}\)g);the second is quenching of the O\({}_{2}\)(a\({}^{1}\Delta_{\text{g}}\)) precursor; the third is sacrificial reactions of the carotenoid with free radicals formed in the photo-initiated reactions. [PERSON] et al. [6] studied the light-induced degradation of various conjugated polymers deposited on glass, including those bearing thiophene and benzothiadiazole electron-accepting units. The photooxidation began even in the presence of trace amounts of oxygen, on the order of several hundreds of ppm, which is easier than in the case of polymers that contain more electron-deficient building blocks.  
We have showed recently that the exposure of subphthalocyanine-based thin films to direct sunlight in air causes both chemical (photodestruction) and morphological (photoan-nealing) processes [7]. Yet, there are issues that need to be clarified. First, it is important to obviate the effect of destructive reactions with gas molecules from ambient [8] or with admixtures coming from the substrate or adjacent layers. Second, from the viewpoint of device stability [9], it is necessary to distinguish between the partial photodestruction of molecules and the soft annealing of the layer, as both processes are likely to arise under prolonged exposure of a sample to sunlight. Just thermal heating of a reference sample in the dark in order to reproduce solar exposure is not fully adequate [10], since the actual temperature up to which the irradiated molecular layer warms up is difficult to control, especially on a non-heat-conducting substrate [11; 12]. Thirdly, it is interesting to know whether all wavelengths absorbed by a molecule initiate (or intensify) the destructive reaction, or only some of them. These issues are addressed here using tris (1,2,5-thiadiazol) subporahrazinatoboron(III) chloride as a new molecular material for optoelectronics [13; 14; 15] and, for comparison, its derivatives with one or three benzene units (i.e., conventional subphthalocyaninato boron(III) chloride, SubPc)--Figure 1.