Olivier Maury (ENS, https://perso.ens-lyon.fr/olivier.maury/)

Old polymethine dyes, discovered in the middle of the XIX^th century for photography application, continue to hold a real fascination in the scientific community owing to their unique spectroscopic properties. In the last decade, these dyes found a renewal of interest for near-infrared (NIR) applications in biological imaging or for the design of advanced photonic materials (laser dyes, nonlinear optics…). Generally speaking, polymethine dyes are charged compounds where the positive (resp. negative) charge is delocalized between two electron-donating (resp. withdrawing) groups via an odd number of sp² carbon atoms. In spite of their wide range of use, the complete rationalization of their very particular photophysical properties remains a matter of debate from both experimental and theoretical points of view.