25th Anniversary Article: Design of Polymethine Dyes for All-Optical Switching Applications: Guidance from Theoretical and Computational Studies

All‐optical switching—controlling light with light—has the potential to meet the ever‐increasing demand for data transmission bandwidth. The development of organic π‐conjugated molecular materials with the requisite properties for all‐optical switching applications has long proven to be a significant challenge. However, recent advances demonstrate that polymethine dyes have the potential to meet the necessary requirements. In this review, we explore the theoretical underpinnings that guide the design of π‐conjugated materials for all‐optical switching applications. We underline, from a computational chemistry standpoint, the relationships among chemical structure, electronic structure, and optical properties that make polymethines such promising materials. Polymethine dyes have the potential to meet the stringent requirements for all‐optical switching applications: that is, controlling light with light. Here, we review the theory behind the design of π‐conjugated molecular materials for all‐optical switching applications and examine the role of computational chemistry in exploring the optical properties of these systems