Stable subphthalocyanine-type dyes with a high electron affinity attract much attention as potential substitutes for traditional fullerenes in molecular electronics devices. One possible way to enhance the acceptor properties of the subphthalocyanine core is by replacing the peripheral benzene fragments (C
6H
4) with 1,2,5-thiadiazole fragments (C
2N
2S
1). However, the resistance of these materials to light or atmospheric effect remains an open question, which limits their further application in device manufacturing. In this work, we compare vacuum-deposited films of three derivatives, SubPzS
3H
0 (all peripheral fragments are 1,2,5-thiadiazoles), SubPzS
2H
4 (two fragments are 1,2,5-thiadiazoles and one fragment is benzene), and SubPcS
0H
12 (all benzenes, i.e., parent subphthalocyanine). Practically relevant substrates were used for deposition, namely, bare glass, glass/ITO or FTO, and PET/ITO. Photobleaching of films under continuous 1 sun illumination was studied in laboratory air, synthetic air, and ultrapure argon. It is shown that the exclusion of near-UV photons from the incident light spectrum, which corresponds to the absorption of subphthalocyanines in the Soret-band, strongly inhibits degradation. Absorption in the Q-band range initiates soft annealing rather than photobleaching of films. The stability of the films deposited on glass decreases as SubPzS
3H
0 > SubPzS
2H
4 > SubPcS
0H
12 in air, and vice versa in argon. The substrate adds more complexity to this picture. In argon, the ITO coating reduces degradation of all of the compounds equally, in contrast to the glass samples, while in air, the SubPzS
3H
0 films discolor completely. The latter reaction proceeds due to the indium-containing species migrating from the conductive coating.
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