Photophysics of organic materials from a computational perspective
In the past few decades, the field of organic electronics has received ever increasing attention, taking organic semiconductors from fundamental research to the hands of billions. However, despite tremendous efforts, the organic light emitting diode (OLED) is the only application to have reached the industrial market. Further improvement of organic materials for given applications requires advanced understanding of their structure-property relationships and underlying photophysical processes. In this talk, I will give an overview of my work in this field from a computational perspective. In particular, I will focus on two topics:
- Materials design for organic electronics requires to go beyond the molecular properties and address the collective behavior of multiple units in active layer thin films that depends on the supramolecular arrangement and nature of intermolecular interactions. This complexity motivated the synthesis and study of discrete multiunit assemblies of conjugated molecules with controlled chemical/geometrical structures and restricted conformational freedom. In a recent combined experimental and theoretical study, we have demonstrated how chemical tuning of a newly synthesized cage architecture allows precise control of the nature of the excited states, opening the way for a rational design of well-defined multichromophoric assemblies.
- Neutral organic radical emitters are currently considered as a promising new route for efficient OLEDs. Using conventional closed-shell materials, electroluminescence efficiency of OLEDs is limited to 25%, as spin statistics dictates that charge recombination leads to 25% singlets and 75% triplets, the latter being intrinsically dark. While several strategies have been proposed to brighten those triplets (inclusion of heavy metal atom, thermally activated delayed fluorescence, etc), the use of radical emitters with spin-allowed doublet emission is a conceptually superior solution to elegantly circumvent the spin statistics limited efficiency issue. Very recently, we have described what is so far the most investigated luminescent organic radical,TTM, and showed how its photophysical properties can be tuned by substitution.