Strongly coupled organic systems are characterized by unusually large Rabi splittings, even in the vacuum state. They show the counter-intuitive feature of a lifetime of the lower polariton state longer than for all other excited states. Here we build up a new theoretical framework to understand the dynamics of such coupled system. In particular, we show that the non-Markovian character of the relaxation of the dressed organic system explains the long lifetime of the lower polariton state.

Herein, we report a homoleptic iron complex bearing tridentate bis‐carbene (CNC) ligands designed for sensitization of TiO2 photoanodes. Its excited state has been characterized by ultra‐fast transient spectroscopy and time‐dependent density functional theory (TD‐DFT) computations, which reveal a record triplet metal‐to‐ligand charge‐transfer (3MLCT) excited‐state lifetime (16 ps). The new dye was efficiently chemisorbed on TiO2 and promoted electron injection and photocurrent generation in a dye‐sensitized solar cell upon solar irradiation.