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 signifi cant 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.