Unconventional and Sustainable Synthesis of Polymethine Dyes: Critical Overview and Perspectives within the Framework of the Twelve Principles of Green Chemistry

Time, energy, and cost saving; waste reduction; health and safety preservation represent true milestones of green chemistry, as well as some of the most important aspects for the industrial synthesis of molecules having relevant technological applications. Herein, in the light of the non-conventional and sustainable approaches towards polymethine dyes that appeared in the literature in the last decade, the twelve principles of green chemistry serve as a guideline for a critical overview of such protocols. The E factor and the EcoScale score for the considered procedures are also assessed, to provide numerical parameters for the evaluation of their impact.