Project R-13048

Triplet excited states in organic semiconducting materials — the role of molecular motives, spin-orbit coupling, and vibrational effects (Research)

A vast number of processes in the excited state dynamics of organic semiconducting materials proceed via the triplet state. In this project, intersystem crossing (ISC), triplet-triplet annihilation (TTA), and room temperature phosphorescence (RTP) are investigated in different series of conjugated donor-acceptor type chromophores. To create a triplet excited state via ISC, spin-orbit coupling (SOC) is required to pair the change in spin (from singlet to triplet) to a change in orbital angular momentum. ISC can be enhanced by the use of heavy atoms such as rare earth metals or even halogens such as bromine and iodine. However, in the envisaged applications of organic light-emitting diodes (OLEDs) and photodynamic therapy (PDT), there is a strong need for heavy-atom free molecules since the strong SOC is paired with a high radiative decay rate for the triplet state (i.e. RTP) and the heavy atoms often lead to unwanted dark cytotoxicity. It has been shown that certain molecular motives or even molecular vibrations can enhance the amount of SOC in fully organic molecules but the underlying fundamental mechanisms remain poorly understood. This project aims to elucidate the origin of these effects and to establish rational structure-property relations through a combination of synthetic efforts, quantum-chemical calculations and dedicated (time-resolved) spectroscopic analysis.

01 October 2022 - 30 September 2025