Owing to their exceptional photophysical properties and high photostability, perylene diimide (PDI) chromophores have found various applications as building blocks of materials for organic electronics. In many light-induced processes in...

Photogenerated multi‐spin systems hold great promise for a range of technological applications in various fields, including molecular spintronics and artificial photosynthesis. However, the further development of these applications, via targeted design of materials with specific magnetic properties, currently still suffers from a lack of understanding of the factors influencing the underlying excited state dynamics and mechanisms on a molecular level. In particular, systematic studies, making use of different techniques to obtain complementary information, are largely missing. This work investigates the photophysics and magnetic properties of a series of three covalently‐linked porphyrin‐trityl compounds, bridged by a phenyl spacer. By combining the results from femtosecond transient absorption and electron paramagnetic resonance spectroscopies, we determine the efficiencies of the competing excited state reaction pathways and characterise the magnetic properties of the individual spin states, formed by the interaction between the chromophore triplet and the stable radical. The differences observed for the three investigated compounds are rationalised in the context of available theoretical models and the implications of the results of this study for the design of a molecular system with an improved intersystem crossing efficiency are discussed.

Linearly coordinated copper(I) carbene complexes, such as [1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]‐(2‐picoline)copper(I) tetrafluoroborate (1), exhibit promising photophysical properties with regard to organic light emitting diode (OLED) applications. Their emission characteristics strongly depend on the surrounding (crystal, matrix, and solution). Here, the behavior of 1 in solution is scrutinized by steady state as well as femtosecond spectroscopy. In coordinating solvents, like acetonitrile and alcohols, 1 is shown to bind solvent molecules as ligands. In non‐coordinating solvents, femtosecond UV/Vis absorption spectroscopy reveals a tri‐exponential decay with time constants of 0.3 ps, 900 ps, and 0.7 μs. The time constants are assigned with the aid of quantum chemistry. A more complex decay is observed in coordinating solvents.

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.

The photophysics of 2-cyanoindole (2-CI) in solution (water, 2,2,2-trifluoroethanol, acetonitrile‚ and tetrahydrofuran) was investigated by steady-state as well as time resolved fluorescence and absorption spectroscopy. The fluorescence quantum yield of 2-cyanoindole is strongly sensitive to the solvent. In water the quantum yield is as low as 4.4 × 10–4. In tetrahydrofuran, it amounts to a yield of 0.057. For 2-CI dissolved in water, a bi-exponential fluorescence decay with time constants of ∼1 ps and ∼8 ps is observed. For short wavelength excitation (266 nm) the initial fluorescence anisotropy is close to zero. For excitation with 310 nm it amounts to 0.2. In water, femtosecond transient absorption reveals that the fluorescence decay is solely due to internal conversion to the ground state. In aprotic solvents, the fluorescence decay takes much longer (acetonitrile: ∼900 ps, tetrahydrofuran: ∼2.6 ns) and intersystem crossing contributes. Graphical abstract