Pot-Economical Approaches to the Synthesis and Functionalization of Phthalocyanines for Clean Energy Production

The last decades have witnessed a growing interest in reducing the ecological and economic impact of chemical processes, with an important focus on the development of more environmentally friendly procedures and methodologies in organic synthesis. Given the extreme versatility and technological importance of phthalocyanines for a variety of applications, of which clean energy production is among the most relevant, the design and study of alternative and less-impacting synthetic approaches to the conventional ones have gained importance in the last years. Their synthesis in solution frequently requires reaction media such as high boiling point alcohols (pentanol, hexanol), dimethylaminoethanol, chlorobenzene, quinoline, and α-chloronaphthalene, most of which are toxic and non-environmentally friendly. Some green synthetic approaches based on solvothermal methods 1,2, mechanochemistry 3, or alternative sources of energy such as microwaves 4-6 and ultraviolet radiation 7, have been developed in order to minimize if not overcome this issue and provide less-impacting experimental conditions for their production. A less studied but very promising approach concerns the development of pot-economical processes, in which two or more reactions take place in the same reaction vessel. The advantage of this approach is twofold: on the one hand it significantly reduces the amount of chemicals required to synthesize and purify a target product, on the other it minimizes the total time required to obtain it. Clearly, the process must be carefully designed in order to avoid yield decreases due to side reactions. In this contribution, the rational design of symmetrical and unsymmetrical substituted phthalocyanines by means of pot-economical approaches in solution will be shown and discussed, along with an estimation of the environmental and economic impact with respect to the related conventional procedures. Examples will be shown both of derivatization of already formed macrocycles, following a “late-stage functionalization” approach 8, and of derivatization of phthalonitriles followed by in-situ metal-templated cyclotetramerization. Furthermore, their optical and electrochemical characterization will be shown, discussed and compared with each other by relating the obtained data to their different chemical structures. Finally, examples of their implementation in the field of organic optoelectronics, with a focus on perovskite solar cells, will be presented. D. Li et al CrystEngComm 2018, 20, 2749–2758. D. Li, et al RSC Adv. 2021, 11, 31226–31234. D. Langerreiter et al Angew. Chem. Int. Ed. 2022, 61, e202209033. A. Shaabani et al Dyes Pigm. 2007, 74, 279–282. D. Villemin et al Molecules 2001, 6, 831–844. A.C.S. Gonzalez et al. J. Porphyr. Phthalocyanines 2020, 24, 947–958. Y. Saito et al Chem-NanoMat 2015, 1, 92–95. G. Zanotti et al ChemPlusChem 2020, 85, 1–12