Sunlight Bleaching of Subporphyrazine Dye Films

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 (C6H4) with 1,2,5-thiadiazole fragments (C2N2S1). 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(3)H(0) (all peripheral fragments are 1,2,5-thiadiazoles), SubPzS(2)H(4) (two fragments are 1,2,5-thiadiazoles and one fragment is benzene), and SubPcS(0)H(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(3)H(0) > SubPzS(2)H(4) > SubPcS(0)H(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(3)H(0) films discolor completely. The latter reaction proceeds due to the indium-containing species migrating from the conductive coating.

Automated summary

Stable subphthalocyanine-type dyes are being considered as potential substitutes for traditional fullerenes in molecular electronics devices due to their high electron affinity. Replacing the peripheral benzene fragments with 1,2,5-thiadiazole fragments can enhance the acceptor properties of the subphthalocyanine core. However, their resistance to light or atmospheric effects remains a challenge, limiting their application in device manufacturing.