Dirk. M. Guldi

Zinc phthalocyanines (ZnPc) have been attached to the peri‐position of a perylenemonoimide (PMI) and a perylenemonoanhydride (PMA), affording electron donor–acceptor conjugates 1 and 2, respectively. In addition, a perylene‐monoimide‐monoanhydride (PMIMA) has been connected to a ZnPc through its imido position to yield the ZnPc‐PMIMA conjugate 10. The three conjugates have been studied for photoinduced electron transfer. For ZnPc‐PMIMA 10, electron transfer occurs upon both ZnPc and PMIMA excitation, giving rise to a long‐lived (340 ps) charge‐separated state. For ZnPc‐PMI 1 and ZnPc‐PMA 2, stabilization of the radical ion pair states by using polar media is necessary. In THF, photoexcitation of either ZnPc or PMI/PMA produces charge‐separated states with lifetimes of 375 and 163 ps, respectively.

A new donor–acceptor system, in which the electron donor triphenylamine (TPA) and the electron acceptor C₆₀ are bridged through a cis‐ or trans‐platinum(II) acetylide spacer have been prepared. Ground‐state studies were conducted using electrochemistry and UV/Vis spectroscopy. Fluorescence studies suggested that charge transfer is the deactivation mechanism for the singlet excited state, and this was verified by transient absorption spectroscopy. Selective photoexcitation of 1 and 2 at 387 nm leads to a fast charge transfer between the TPA and C₆₀, which gives rise to a radical ion‐pair state (TPA^.+–Pt–C₆₀^.−). Our results suggest that charge transfer is favored for the cis configuration while the presence of the trans configuration in the Pt^II diacetylide results in a longer‐lived charge separated states.

A new series of donor–bridge–acceptor (D–B–A) compounds consisting of π‐conjugated oligofluorene (oFL) bridges between a ferrocene (Fc) electron‐donor and a fullerene (C₆₀) electron‐acceptor have been synthesized. In addition to varying the length of the bridge (i.e., mono‐ and bi‐fluorene derivatives), four different ways of linking ferrocene to the bridge have been examined. The Fc moiety is linked to oFL: 1) directly without any spacer, 2) by an ethynyl linkage, 3) by a vinylene linkage, and 4) by a p‐phenylene unit. The electronic interactions between the electroactive species have been characterized by cyclic voltammetry, absorption, fluorescence, and transient absorption spectroscopy in combination with quantum chemical calculations. The calculations reveal exceptionally close energy‐matching between the Fc and the oFL units, which results in strong electronic‐coupling. Hence, intramolecular charge‐transfer may easily occur upon exciting either the oFLs or Fcs. Photoexcitation of Fc–oFL–C₆₀ conjugates results in transient radical‐ion‐pair states. The mode of linkage of the Fc and FL bridge has a profound effect on the photophysical properties. Whereas intramolecular charge‐separation is found to occur rather independently of the distance, the linker between Fc and oFL acts (at least in oFL) as a bottleneck and significantly impacts the intramolecular charge‐separation rates, resulting in beta values between β_CS 0.08 and 0.19 Å⁻¹. In contrast, charge recombination depends strongly on the electron‐donor–acceptor distance, but not at all on the linker. A value of β_CR (0.35±0.01 Å⁻¹) was found for all the systems studied. Oligofluorenes prove, therefore, to be excellent bridges for probing how small structural variations affect charge transport in D–B–A systems.

Two novel double‐alkyl functionalized imidazolium ionic liquid crystals have successfully been utilized to demonstrate the benefits of the liquid crystalline phase on the ssDSSC performance. In particular, a good balance between dye regeneration and hole transport is only realized in the liquid crystalline phase. Devices that employ a single component ionic liquid based electrolyte show a remarkably stable efficiency during 1000 h under outdoor operation temperature conditions and 1 sun illumination.

In contrast to pristine zinc phthalocyanine (1), zinc phthalocyanine based oPPV‐oligomers (2–4) of different chain lengths interact tightly and reversibly with graphite, affording stable and finely dispersed suspensions of mono‐ to few‐layer graphene—nanographene (NG)—that are photoactive. The p‐type character of the oPPV backbones and the increasing length of the oPPV backbones facilitate the overall π–π interactions with the graphene layers. In NG/2, NG/3, and NG/4 hybrids, strong electronic coupling between the individual components gives rise to charge transfer from the photoexcited zinc phthalocyanines to NG to form hundreds of picoseconds lived charge transfer states. The resulting features, namely photo‐ and redoxactivity, serve as incentives to construct and to test novel solar cells. Solar cells made out of NG/4 feature stable and repeatable photocurrent generation during several ‘on‐off’ cycles of illumination with monochromatic IPCE values of around 1%.

Facing facts: Coordination of Cp*Ru (Cp*=C₅Me₅) to the concave and convex π surfaces of subphthalocyanines constitutes a new approach to the functionalization of subazaporphyrins. While the convex face shows higher reactivity, coordination to the concave side produces a stronger diatropic influence on the Cp* ligand and a greater perturbation of the macrocyclic π‐electronic features.