The synthesis and scanning tunneling microscopy (STM) investigations of shape-persistent arylene-ethynylene-butadiynylene macrocycles along with their codeposites with metallacycles are reported. 2D ordered arrays of macrocycles and macrocycle/metallacycle architectures (1:1) have been obtained on HOPG by self-assembly under ambient conditions. It is found that the ordered macrocycle array acts as a template for the deposition of the adlayer molecules. For each underlying macrocycle, one metallacycle has been detected. The unit-cell data of both, the macrocycles and their codeposites, show that the structural information of the macrocycle layer is perfectly transformed to the guest molecules. A rather unexpected observation is that the present compound could not be coadsorbed with C(60), indicating that only a minor change in the structure of the macrocycle has a dramatic effect on the ability of the monolayer to bind additional guest molecules.

No abstract

No abstract

No abstract

No abstract

Dual singlet-triplet fluorescence-phosphorescence emitting compounds demonstrate that plasmonic surface enhancement is controlled solely by the underlying oscillator strength of a transition: metal-free compounds with weak spin-orbit coupling show no enhancement in phosphorescence efficiency even though fluorescence is amplified.Excitement in the area of plasmonics stems from the ability to detect processes that are otherwise undetectable. Collective electron oscillations at metal surfaces experience strong spatial localization, which results in extremely intense and localized electromagnetic fields. This phenomenon is at the heart of all surface-enhanced spectroscopic processes. 1 The intense local field can relax several selection rules, thereby allowing transitions that are otherwise forbidden, and are therefore inaccessible to regular spectroscopy. While observation of forbidden Raman modes in surface-enhanced Raman scattering (SERS) is well documented, 2 the same is not as common for electronic transitions. Particularly noteworthy is a report on the observation of dipole-forbidden, but quadrupole-allowed transitions in conjugated oligoenes near silver films. 3 A crucial question to explore is hence whether metal nanostructures can also enhance dipole-forbidden radiative recombination from triplet excited states, phosphorescence. The necessity arises because 75% of radical-pair recombination events in an organic light-emitting diode (OLED) lead to triplet excited states that generally have poor radiative recombination efficiency in the absence of heavy-metal atoms. There have been a few reports on plasmon-enhanced phosphorescence. 4 One aspect common to these studies is that the effect was investigated in materials that are strongly spin-orbit (SO) coupled and thus highly phosphorescent to begin with. Most hydrocarbon organic semiconductors are weakly phosphorescent. OLED electrodes provide a natural environment for surface enhancement. If surface enhancement were to apply to transitions involving pure triplet and singlet states, in the absence of SO-induced spin mixing, the mechanism could open a new intrinsic radiative channel in an OLED, changing the way triplet harvesting is achieved and removing present limitations on triplet emitters posed by organometallic chemistry.Unfortunately, as we demonstrate here, this approach will not succeed. Phosphorescence can only be enhanced by plasmonics when intersystem crossing (ISC) is already strong. Surprisingly, phosphorescence due to transitions between pure triplet and singlet states is not enhanced to any measurable extent by plasmonic effects, even though a strong increase in fluorescence is observed in dual singlet-triplet-emitting compounds.To assess the possibility of surface enhancement of phosphorescence, we need an independent observable to confirm the presence of an enhancement effect. This observable is given by the dipole-allowed singlet transition in the dual-emitting compounds shown in Fig. 1a. We chose four materials with variable triplet yield (...

The synthesis and characterization of a shape-persistent triphenylene-butadiynylene macrocycle formed by intermolecular Glaser-coupling of two ''half-rings'' and also by intramolecular coupling of the appropriate open dimer, respectively, are described in detail. The investigation of the photophysics has revealed that-compared to its open dimer-the macrocycle is more conjugated in the ground state and less so in the excited state, a result of the diacetylene bending in the macrocycle due to its constrained topology. The macrocycle is decorated with flexible side groups that support its adsorption on highly oriented pyrolytic graphite (HOPG) where a concentration-dependence of the 2D-structure is observed by means of scanning tunnelling microscopy (STM). The flexible side groups also guarantee a high compound solubility even in nonpolar solvents (cyclohexane). However, solvophobic interactions lead to the formation of a tube-like superstructure, as revealed by dynamic light scattering, X-ray scattering and atomic force microscopy.

In the past, benzotriazole acceptor units have been incorporated successfully into donor−acceptor polymers for highly efficient photovoltaic devices. Here, we explore 2phenyl-2H-benzotriazole oligomers as model systems for donor−acceptor polymers. We designed and synthesized acceptor−donor−acceptor oligomers incorporating 2-phenyl-2Hbenzotriazole acceptor and naphthodithiophene donor units. Supported by quantum chemical calculations we investigated the optoelectronic properties, such as electronic levels and intramolecular charge transfer, by means of optical and fluorescence spectroscopy. We built bulk-heterojunction solar cells comprising these oligomers and [6,6]-phenyl C 61 -butyric acid methyl ester. In doing so, the film-forming conditions were optimized as the absorber layer morphology is strongly affected by the deposition conditions, in particular drying time and drying temperature.