4. Outlook and developments

The unique behavior of compound 2 lies in the combination of TADF and ESA properties. ESA generally requires a material characterized by a highly permissive absorption transition, which is the case for molecule 2 due to its planar geometry, which favors electron delocalization. But this contradicts the possibility of observing TADF emission, which is linked to the non-delocalized nature of the molecular orbitals. In the case of compound 2, it has been demonstrated that another type of mechanism is at play in the excited states to explain the effectiveness of TADF. It is based on the coupling of excited electronic states with vibration modes characteristic of the molecule during the inverse intersystem crossover transition. The study thus makes a new contribution to fundamental knowledge of the photophysics of organic dyes, and also opens up the possibility of applications in the field of...