Sustainable approaches to the synthesis and functionalization of state-of-art and novel phthalocyanines for technological applications

In recent decades, particular attention has been paid to the issue of sustainability by encouraging the development of technologies with low environmental and economic impact. It is a transversal approach that is gaining momentum in all sectors of industry, especially in the chemical industry and research. Given the extreme versatility and technological importance of phthalocyanines, the design and study of alternative synthetic approaches to the conventional ones have gained importance in the last few years. Phthalocyanines are commonly synthesized on lab-scale by tetramerization of phthalonitriles with lithium alcolates or strong organic bases in environmentally impacting reaction media like alkyl alcohols or aromatic organic solvents. Further state-of-the-art protocols exploit melting methods from phthalic anhydride at high temperatures (200-300°C), microwave-assisted processes, synthesis in ionic liquids and syntheses performed at room temperature catalyzed by strong organic bases such as lithium diisopropylamide (LDA). [1, 2, 3] Even though moving towards an increased sustainability, these alternative synthetic routes often suffer from lack of scalability, thus may result difficult to realize on a large scale. In this context, the idea of approaching the synthesis of phthalocyanines exploiting classical solution processes by applying green chemistry principles was developed. In this contribution, the use of more sustainable solvents and purification methods [4] as well as the rational design of electron-rich symmetrically substituted phthalocyanines by means of pot-economical approaches will be shown and discussed, along with an estimation of the environmental and economic impact with respect to the related established procedures. Optoelectrochemical characterizations of the synthesized materials hint at the possibility of their application in the field of organic electronics and perovskite solar cells. REFERENCES 1. W. Zheng, C. Z. Wan, J.X. Zhang,, C.H. Li, X. Z. You, X.Z.Tetrahedron Lett., 2015, 56, 4459-4462. 2. Ö. Koyun, S. Gördük, B. I. Keskin, A. Çetinkaya, A. I. Koca, U. Avciata, Polyhedron, 2016,113, 35-49. 3. P-C. Lo, D. Y. Y. Cheng, D. K. P. Ng, Synthesis, 2005, 7, 1141-1147. 4. G. Zanotti, P. Imperatori, A. M. Paoletti, G. Pennesi, Molecules, 2021, 26, 1760.