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Im Rahmen dieser Arbeit wurde die Herstellung der ersten Klasse von stabilen neutralen homoaromatischen Kohlenwasserstoffen, den Homoannulenen, etabliert. Ihre Zuordnung zu den Homoaromaten wurde systematisch anhand der Kriterien für Homoaromatizität durchgeführt. Experimentell wurde das magnetische Kriterium verifiziert, da in den Homoannulenen indirekt ein Ringstrom nachgewiesen wurde, was durch einen beobachteten Ringstromeffekt mittels NMR-Spektroskopie untermauert wurde. Durch die Analyse der Bindungslängen (erhalten durch Röntgenbeugungsanalyse an Einkristallen) wurde das geometrische Kriterium bestätigt, da eine signifikante Angleichung der Bindungslängen in den Homoannulenen festgestellt wurde. Neben den experimentell gewonnenen Indizien wurden auch quantenchemische Berechnungen durchgeführt (wie NICS- und ACID- Analyse), die mit den experimentellen erhaltenden Daten übereinstimmen. Die experimentellen und computerchemischen Daten deuteten darauf hin, dass Homoannulene moderate globale 10pi neutrale Homoaromaten sind, wobei eine verstärkte lokale Homoaromatizität im 6pi System des Cycloheptatrienyl-Fragmentes beobachtet wurde. Darüber hinaus wurde bei der Funktionalisierung von Homoannulenen eine Reaktivität vergleichbar zu Aromaten beobachtet, weil sie ähnlich wie in aromatischen Substitutionsreaktionen reagierten. Es zeigte sich, dass Homoannulene eine reversible photochemisch induzierte [1,11] sigmatrope Umlagerung zu Isohomoannulen durchlaufen, was Homoannulene strukturell zu neuartigen Photoschaltern macht. Darüber hinaus legen quantenchemische Berechnungen nahe, dass Isohomoannulen ein 10pi homoaromatisches System ist.

Some molecular photoisomers can be isomerized to a metastable high-energy state by exposure to light. These molecules can then be thermally or catalytically converted back to their initial state, releasing heat in the process. Such a reversible photochemical process has been considered for developing molecular solar thermal (MOST) systems. In this review, we introduce the concept, criteria, and state-of-the-art of MOST systems, with an emphasis on the three most promising molecular systems: norbornadiene/quadricyclane, E/Z-azobenzene, and dihydroazulene/vinylheptafulvene. After discussing the fundamental working principles, we focus on molecular design strategies for improving solar energy storage performance, remaining challenges, and potential focus areas. Finally, we summarize the current molecular incorporation into functional devices and conclude with a perspective on challenges and future directions.

Some molecular photoisomers can be isomerized to a metastable high-energy state by exposure to light. These molecules can then be thermally or catalytically converted back to their initial state, releasing heat in the process. Such a reversible photochemical process has been considered for developing molecular solar thermal (MOST) systems. In this review, we introduce the concept, criteria, and state-of-the-art of MOST systems, with an emphasis on the three most promising molecular systems: norbornadiene/quadricyclane, E/Z-azobenzene, and dihydroazulene/vinylheptafulvene. After discussing the fundamental working principles, we focus on molecular design strategies for improving solar energy storage performance, remaining challenges, and potential focus areas. Finally, we summarize the current molecular incorporation into functional devices and conclude with a perspective on challenges and future directions.

Some molecular photoisomers can be isomerized to a metastable high-energy state by exposure to light. These molecules can then be thermally or catalytically converted back to their initial state, releasing heat in the process. Such a reversible photochemical process has been considered for developing molecular solar thermal (MOST) systems. In this review, we introduce the concept, criteria, and state-of-the-art of MOST systems, with an emphasis on the three most promising molecular systems: norbornadiene/quadricyclane, E/Z-azobenzene, and dihydroazulene/vinylheptafulvene. After discussing the fundamental working principles, we focus on molecular design strategies for improving solar energy storage performance, remaining challenges, and potential focus areas. Finally, we summarize the current molecular incorporation into functional devices and conclude with a perspective on challenges and future directions.

We present a new concept to control the conformations of molecules in the excited state through harvesting negative hyperconjugation. The strategy was realized with the 2,3,1,4-benzodiazadiborinane scaffold, which was prepared by a new synthetic procedure. Photochemical studies identified dual light emission, which was assigned to well-defined conformers. The emission at longer wavelength can be switched off by restricting the rotational degrees of freedom in the solid state as well as by controlling the energy levels of the excited states through adjusting the solvent polarity.

We present a new concept to control the conformations of molecules in the excited state through harvesting negative hyperconjugation. The strategy was realized with the 2,3,1,4-benzodiazadiborinane scaffold, which was prepared by a new synthetic procedure. Photochemical studies identified dual light emission, which was assigned to well-defined conformers. The emission at longer wavelength can be switched off by restricting the rotational degrees of freedom in the solid state as well as by controlling the energy levels of the excited states through adjusting the solvent polarity.

We report an air-stable bisboron complex as an efficient catalyst for the inverse electron-demand Diels-Alder (IEDDA) reaction of 1,2-diazine as well as 1,2,4,5-tetrazine. Its stability towards air and moisture was demonstrated by NMR studies enabling its application in organic transformations without glovebox. A one-pot procedure for its synthesis was developed starting from 1,2-bis(trimethylsilyl) benzene greatly enhancing its practicality. Comparative reactions were carried out to evaluate its catalytic activity in IEDDA reactions of diazine including phthalazine as well as 1,2,4,5-tetrazine.

We report an air-stable bisboron complex as an efficient catalyst for the inverse electron-demand Diels-Alder (IEDDA) reaction of 1,2-diazine as well as 1,2,4,5-tetrazine. Its stability towards air and moisture was demonstrated by NMR studies enabling its application in organic transformations without glovebox. A one-pot procedure for its synthesis was developed starting from 1,2-bis(trimethylsilyl) benzene greatly enhancing its practicality. Comparative reactions were carried out to evaluate its catalytic activity in IEDDA reactions of diazine including phthalazine as well as 1,2,4,5-tetrazine.

A small single molecule with multiple photoswitchable subunits, selectively and independently controllable by light of different wavelengths, is highly attractive for applications in multi-responsive materials and biological sciences. Herein, triple photoswitches are presented consisting of three independent azobenzene (AB) subunits that share a common central phenyl ring: the meta-trisazobenzenes (MTA). It is the unique meta-connectivity pattern leading to decoupling of all azo-subunits although they do overlap spatially. Based on this pattern, we design a triple MTA photoswitch, as proof-of-principle, with three different, electronically independent AB branches on the computer, which can be individually photo-excited to trigger ultra-fast E → Z isomerization at the selected AB branch.

We investigated the adsorption of corannulene (C20H10) on the Ag(111) surface by experimental and simulated scanning tunneling microscopy (STM), X-ray photoemission (XPS) and near-edge X-ray absorption fine structure (NEXAFS). Structural optimizations of the adsorbed molecules were performed by density functional theory (DFT) and the core excited spectra evaluated within the transition potential approach. Corannulene is physisorbed in a bowl-up orientation displaying a very high mobility (diffusing) and dynamics (tilting and spinning) at room temperature. At the monolayer saturation coverage, molecules order into a close compact phase with an average intermolecular spacing of ∼10.5±0.5Å. The lattice mismatch drives a long wavelength structural modulation of the molecular rows, which, however, could not be identified with a specific superlattice periodicity. DFT calculations indicate that the structural and spectroscopic properties are intermediate between those predicted for the limiting cases of an on-hexagon geometry (with a three-fold, ∼8.6Å unit mesh) and an on-pentagon (with a four-fold, ∼11.5Å unit mesh). We suggest that molecules smoothly change their equilibrium configuration along the observed long wavelength modulation of the molecular rows by varying their tilt and azimuth in between the geometric constraints calculated for molecules in the three-fold and four-fold phases

Recently, we described the first inverse electron demand Diels-Alder reaction of 1,2-diazene catalyzed by a bidentate Lewis acid. Herein we investigate 1,2-phenylenediboronic esters as potential catalysts for this transformation offering higher stability and easier handling than the currently used boranthracene derivatives. Different 1,2-phenylenediboronic esters were prepared and their ability to form bidentate coordination complexes with phthalazine was analyzed. Although a 1:1 complex was observed, X-ray analysis revealed binding only in a monodentate fashion. Graphical abstract

We report the formation of a stable neutral diboron diradical simply by coordination of an aromatic dinitrogen compound to an ortho-phenyldiborane. This process is reversible upon addition of pyridine. The diradical species is stable above 200 degrees C. Computations are consistent with an open-shell triplet diradical with a very small open-shell singlet-triplet energy gap that is indicative of the electronic disjointness of the two radical sites. This opens a new way of generating stable radicals with fascinating electronic properties useful for a large variety of applications.

We report the formation of a stable neutral diboron diradical simply by coordination of an aromatic dinitrogen compound to an ortho-phenyldiborane. This process is reversible upon addition of pyridine. The diradical species is stable above 200 degrees C. Computations are consistent with an open-shell triplet diradical with a very small open-shell singlet-triplet energy gap that is indicative of the electronic disjointness of the two radical sites. This opens a new way of generating stable radicals with fascinating electronic properties useful for a large variety of applications.

A new modular approach to the smallest substituted cycloparaphenylenes (CPPs) is presented. This versatile method permits access to substituted CPPs, choosing the substituent at a late stage of the synthesis. Variously substituted [8]CPPs have been synthesized, and their properties analyzed. The structural characteristics of substituted CPPs are close to those of unsubstituted CPPs. However, their optoelectronic behavior differs remarkably due to the larger torsion angle between the phenyl units.

Recently, we described the first inverse electron demand Diels-Alder reaction of 1,2-diazene catalyzed by a bidentate Lewis acid. Herein we investigate 1,2-phenylenediboronic esters as potential catalysts for this transformation offering higher stability and easier handling than the currently used boranthracene derivatives. Different 1,2-phenylenediboronic esters were prepared and their ability to form bidentate coordination complexes with phthalazine was analyzed. Although a 1:1 complex was observed, X-ray analysis revealed binding only in a monodentate fashion. Graphical abstract