An acridone derivative (N-methyl-difluoro-acridone, NMA-dF) is characterized with respect to its utility as an emitter in organic light emitting diodes (OLEDs). Using steadystate and time-resolved spectroscopy as well as quantum chemistry, its ability to convert singlet and triplet excitons into light was scrutinized. NMA-dF emits in the deep blue range of the visible spectrum. Its fluorescence emission occurs with quantum yields close to 1 and a radiative rate constant of ≈5 × 10 8 s −1 . So, it processes singlet excitons very efficiently. Using 1,4-dichlorobenzene as a sensitizer, it is shown that NMA-dF also converts triplet excitons into light. With the aid of quantum chemistry, this is related to a reverse intersystem crossing starting from a higher triplet state (HIGHrISC).

The photophysics of N-methylphthalimide (MP) in solution (cyclohexane, ethanol, acetonitrile, and water) was characterized by steady state as well as time resolved fluorescence and absorption spectroscopy.

The psoralens 8-methoxypsoralen (8-MOP), 4,5′,8-trimethylpsoralen (TMP) and 5-methoxypsoralen (5-MOP) find clinical application in PUVA (psoralen + UVA) therapy. PUVA treats skin diseases like psoriasis and atopic eczema. Psoralens target the DNA of cells. Upon photo-excitation psoralens bind to the DNA base thymine. This photo-binding was studied using steady-state UV/Vis and IR spectroscopy as well as nanosecond transient UV/Vis absorption. The experiments show that the photo-addition of 8-MOP and TMP involve the psoralen triplet state and a biradical intermediate. 5-MOP forms a structurally different photo-product. Its formation could not be traced by the present spectroscopic technique.

The photophysics of dibenzo [a,j]phenazine (DBPHZ) in solution was investigated by steady-state and time-resolved spectroscopy. The nature of the solvent (methanol, acetonitrile, dichloromethane and cyclohexane were considered) only weakly affects the photophysical properties. The first excited singlet state features a lifetime of the order of 1 ns. Its fluorescence emission is centered around 420 nm and occurs with moderate yields of � 0.1. The lowest triplet state is populated with yields of � 0.3. Quantum chemical computations suggest that a 3 np * state energetically close to the primarily excited singlet state is responsible for the efficient intersystem crossing towards the triplet manifold.

The photophysics of a thermally activated delayed fluorescence (TADF) emitting macrocycle consisting of two dibenzo[ a,j ]phenazine acceptor moieties bridged by two N,N,N’,N’ ‐tetraphenylene‐1,4‐diamine donor units was scrutinized in solution by steady‐state and time‐resolved spectroscopy. The fluorescence lifetime of the compound proved to be strongly solvent‐dependent. It ranges from 6.3 ns in cyclohexane to 34 ps in dimethyl sulfoxide. In polar solvents the fluorescence decay is predominantly due to internal conversion. In non‐polar ones radiative decay and intersystem crossing contribute. Contrary to the behaviour in polymer matrices (S. Izumi et al., J. Am. Chem. Soc . 2020 , 142 , 1482) the excited state decay is not predominantly due to prompt and delayed fluorescence. The solvent‐dependent behaviour is analyzed with the aid of quantum chemical computations.