How can catalytic reactions be discovered? Here, a two-dimensional screening strategy for reaction discovery is described. For this purpose, the investigation of single mechanistic steps is merged with combinatorial screening. As a showcase, application to the field of visible light photocatalysis allowed for the discovery of three unexpected cyclization reactions. Extensive mechanistic analysis by advanced spectroscopic and computational tools enabled insights into the underlying molecular processes. In particular, a significantly endergonic sensitization event could be discovered and substantiated by transient absorption spectroscopy.

We describe for the first time the full reaction coordinate regarding the photoisomerization of red-absorbing norbornadienes (NBDs) to quadricyclanes (QCs). Our studies go beyond steady-state investigations by using an arsenal of timeresolved techniques. Importantly, the red absorption of NBDs is made possible by a different charge-transfer character; adjusting its strength enables control over the photoreversibility of the rearrangement. In the case of strong charge-transfer character (a weakly electron-withdrawing ester and a strongly electron-donating dimethylaniline), photoirradiation with visible light into the delocalized charge-transfer absorption of NBD affords QC reversibly. In stark contrast, UV photoirradiation into the NBD localized excited state leads to a photoinduced degradation and cannot be back-isomerized to NBD under any circumstances. If the charge-transfer character is weak (a weakly electron-withdrawing ester and a weakly electron-donating phenyl), reversibility is seen independently of the photoirradiation light.

Two novel homo and hetero three-dimensional nanographenes, NG1 and NG2, featuring a cyclooctatetraene core are designed, synthesized, and characterized. A concise and efficient bottom-up methodology was employed during which 24 new carbon−carbon bonds were formed. By means of a Scholl reaction nanographenes with 53 fused rings are realized, which exhibited good solubility in common organic solvents. The resulting saddle-like structures of NG1 and NG2 are electron-rich and show good chemical and electrochemical stability. Their molecular structures are fully elucidated by single-crystal X-ray crystallography. From their crystal structure analysis is concluded that both nanographenes are chiral and crystallize as a racemic mixture. Our work was rounded-off by excited state investigations such as electron and energy transfer with electron-acceptors and -donors.

Dendrimer−dye assemblies are used as novel supramolecular nanoreactors for the formation of various gold nanostructures. The organic−inorganic hybrid systems are investigated with dynamic light scattering, UV−vis spectroscopy, and transmission electron microscopy (TEM) as well as cryo-TEM and high-resolution TEM (HRTEM). We show that the shape of the hybrid assemblies is determined by the choice and the ratio of the building blocks. Shape and size of the gold nanoparticles within the assemblies are controlled by the reducing agent. The accessible range of gold morphologies extends from small and spherical, over ellipsoidal, faceted, and large to highly anisotropic. The approach may open the way to new hybrid systems with applications in catalysis or in the biomedical field.

Cyclopenta[hi]aceanthrylenes (CPAs) have been functionalized at two of the peripheral positions with electronically inert trimethylsilylethynyl (1), as well as with electron‐donating 4‐ethynyl‐N,N‐dimethylaniline (2), ethynyl ZnIIphthalocyanine (3), and ethynyl ZnIIporphyrin (4) units. Consistent with X‐ray crystal structures of 2 and 4, analyses of absorption and fluorescence of 2–4 point to strong electronic communication between the CPA and the peripheral units, affording quadrupolar electron donor‐acceptor‐donor charge‐transfer conjugates. By virtue of their quadrupolar/dipolar charge‐transfer characters in the excited state, 2–4 exhibit fluoro‐solvatochromism. Transient absorption spectroscopy confirmed delocalized quadrupolar ground states and formation of weakly solvent stabilized quadrupolar singlet excited states. The latter transform into strongly stabilized dipolar excited states before deactivating to the ground state in 2 and give rise to a fully charge separated state in 3 and 4.