The cyclopentadienone-fused dihydropyrenes 46 and 47 were synthesized. The internal methyl resonances, the coupling constants, NICS calculations and X-ray results confirmed that the cyclopentadienone displays antiaromatic character resulting in bond localization in the annulene ring consistent with a 4n-pi fused system. The ring current of the dihydropyrene fragment is reduced by fusion of the antiaromatic system by about 80% of that caused by benzene. The syntheses of the methylfulvene fused dihydropyrene 56 and the phenylfulvene fused dihydropyrene 58 have been accomplished. The calculated and experimental NMR data and NICS calculations all demonstrated that the fulvenes had weak diatropic ring currents and caused bond localizations in the DHP rings, in which phenyl fulvene has a larger effect than that of methyl fulvene. A number of bis-dihydropyrene systems, bis-dihydropyrene ketone 117, bis-benzo[e]dihydropyrene ketone 119, benzo[e]dihydropyrene dihydropyrene ketone 122, bis-benzo[e]dihydropyrene methylene 124 and the benzo[e]dihydropyrene- dihydropyrene acetylene 130, have been synthesized, in which 117, 119 and 124 are homo-systems and 122 and 130 are hetero-systems. The multiple photoswitching properties study found that all of these systems except 130 showed multi-states during the photo opening and photo closing processes, which means that each end of the DHP units photo opens or closes separately rather than synchronously. In the homo switches 117, 119 and 124, the two DHP units act independently, but the relative differentiation is not very significant. On the other hand, the hetero-switch 122 showed fully differentiated photo opening process and almost a pure open-closed intermediate 122’ could be achieved. This is the first example which clearly showed four states in the UV closing process. The relative photo opening and closing rates compared to benzoDHP 36 have also been studied. It was found that while the carbonyl linker largely increased the relative photo opening rate (117, 119 and 122), the methylene linker only increased it slightly (124). The photo closing processes were always fast as usual. The studies of the thermal return reactions of these systems showed that while the carbonyl linker substantially slowed down the thermal return reactions of the DHP units (117, 119 and 122), the methylene linker speeded it up slightly (124). The mono-iron tricarbonyl benzo[e]dihydropyrene complex 152, the bis-iron tricarbonyl benzo[e]dihydropyrene complex 153 and the iron tetracarbonyl dihydropyrene complex 151 were synthesized. The structures of 152 and 153 were determined by X-ray crystallography. The coordinations of iron tricarbonyl moieties to the DHP rings caused a distortion of ca. 30 degree away from the central DHP plane. Coordination also increased bond alternation and reduced ring currents in the DHP rings. 1H-NMR and X-ray studies showed that 152 showed a weak paratropic ring current in the DHP ring. Iron coordination of the DHP completely stopped the photochromic properties of the dihydropyrenes.

Gegenstand dieser Arbeit ist die Frage wie thermische und photochemische Gleichgewichte verbunden werden können und sich gegenseitig beeinflussen. Dazu wurden zwei Projekte bearbeitet, zum einen das Konzept der „säure-katalysierten Zykloreversion“ und zum anderen das Konzept der „licht-induzierten pKs Veränderung“. Im ersten Konzepte wurde eine extern steuerbare, thermische Rückreaktion genutzt, um die Zusammensetzung im photostationären Zustand zu kontrollieren. Durch Zugabe von katalytischen Mengen einer starken Säure wurde die Ringöffnung eines Diarylethens, welches mit einem Flurenol substituiert ist, eingeleitet. Der zugrundeliegende Prozess wurde kinetisch und thermodynamisch, sowohl durch Experimente als auch durch computergestützte Rechnungen beschrieben. Eine säure-induzierte Dehydratation öffnet einen neuen Reaktionspfad, wodurch die normalerweise sehr hohe Reaktionsbarriere der Ringöffnung umgangen werden kann. Die quantitative Umsetzung mit Säure führt zu einer kompletten Löschung der photochemischen Reaktivität. Dieses Konzept kann in der Speicherung von Lichtenergie in photochromen metastabilen Systemen genutzt werden. Durch die Nutzung von 3-H-Thiazol-2-on als Rest im Diarylethen konnte eine signifikante pKs Änderung von 2.8 Einheiten in wässriger Umgebung erreicht werden. Dabei wurden zwei Säure-Base Gleichgewichtssysteme miteinander gekoppelt, welche an der thermischen Umwandlung gehindert sind, jedoch photochemisch ineinander überführt werden können. Des Weiteren wurde eine hohe Abhängigkeit der Quantenausbeute von dem Protonierung festgestellt. Diese wurde genutzt um die Performance der Photoreaktion zu beeinflussen. Die Beeinflussung der Photoreaktion erfolgt nicht durch Veränderung der Energetik des Grundzustandes, sondern durch Veränderung der Potentialhyperfläche des angeregten Zustandes. Durch neue molekulare Designs konnte eine signifikante Verbesserung im Vergleich zu bekannter Molekülen und Konzepten in beiden Projekten erreicht werden. / Two projects are implemented in this work, which share the goal to interconnect acid-base equilibria with the photoreactions of diarylethene (DAE) photoswitches. This task can be divided into two logic questions: How can photochemical equilibria be controlled or rather influenced via an acidic or basic stimulus and how can a photoreaction induce control over an acid-base equilibrium? In the first project, “Acid-Catalyzed Cycloreversion”, an externally tunable thermal back reaction was designed to influence a photochemical equilibrium. Upon addition of catalytic amounts of acid, a closed DAE carrying a fluorenol moiety undergoes facile thermal ring opening. The underlying thermodynamics and kinetics of the entire system have been analyzed experimentally as well as computationally. Appling an excess of acid leads to a complete inhibition of the photoreaction through the introduction of a charge-transfer. My work suggests that acid catalysis provides a useful tool to bypass thermal barriers, potentially usable to efficiently trigger the release of light energy stored in photoswitches. In the second project, entitled “Light-induced pKa Modulation”, a significant pKa change of 2.8 units in an aqueous medium was achieved by connecting two different acid-base equilibria. These thermodynamic equilibria are separated by a high activation barrier, overcome by a photoreaction. The developed system which is based on the incorporation of a 3 H thiazol 2 one moiety into a DAE, shows a strong dependency of the quantum yield and hence, of the photoconversion on the protonation state. Adjusting the pH within the range of the pKa change, a substantial enhancement of the photoconversion is achievable as well as a distinct alteration of the performance of the photoreaction. This effect does not originate from different reaction paths on the ground state potential energy surface (PES), but results presumably from a protonated state dependent difference in the excited PES.