Synthesis and Optoelectronic Properties of Janus-Dendrimer-Type Multivalent Donor–Acceptor Systems

Abstract

A convergent, multistep protocol was employed for the synthesis of a Janus-type multivalent donor-acceptor system. The synthetic approach is based on a Sonogashira cross-coupling of two differently ferrocene-(Fc) substituted dendrons and a final sixfold [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) reaction with tetracyanoethene, which occurs regioselectively at only one of the rigidly linked dendrons. The structural and optoelectronic properties of the compounds were investigated by X-ray analysis, UV/vis spectroscopy, and electrochemistry. The target Janus-system displays redox-amphoteric behavior. The nonalkynylated Fc end groups in one dendron are readily and reversibly oxidized. The second dendron, in which the terminal Fc-activated alkynes underwent the CA-RE reaction to give tetracyanobuta-1,3-dienes in the final step of the synthesis, undergoes four reversible 3-e(-) reductions in the very narrow potential range of 1 V. A spontaneous intramolecular charge transfer from the donor into the acceptor hemisphere was not observed. Furthermore, the oxidation potential of the Fc donors in one hemisphere is hardly perturbed by the push-pull acceptors in the other, which suggests that electronic communication along the π-system, with several meta-connectivities, is not efficient. Therefore, the charge-transfer bands seen in the Janus-type system originate from the interaction of the Fc donors with the directly connected tetracyanobuta-1,3-diene acceptors in the same hemisphere.

Janus second-order nonlinear optical dendrimers: their controllable molecular topology and corresponding largely enhanced performance

“…The dual-functionalized surfaces endow the dendrimers with different properties, which has allowed them be widely used in self-assembly 10 and biological therapeutics. 11 However, their applications in optoelectronic materials are very scarce until now, 12 partially because the photo- and electronic properties mainly depend on the electronic structure of the repeat unit instead of the peripheral groups. Nevertheless, we guess that a Janus dendrimer would possess huge potential advantages in this area, for at least, the asymmetric features of “Janus” exactly meets the requirement of a non-centrosymmetric alignment of chromophore moieties in second order nonlinear optical (NLO) polymers, which has never been reported previously.…”

Multifunctional triazolylferrocenyl Janus dendron: Nanoparticle stabilizer, smart drug carrier and supramolecular nanoreactor

“…Janus dendrimers (JDs) are newly emerging types of dendrimers and are normally constructed of two different dendrons with varying size and functionality to obtain a single amphiphilic or heterofunctional macromolecule . Their asymmetric structures lead to new and efficient characteristic properties for the formation of complex self‐assembled materials that are presently inconceivable for homogeneous or symmetric dendrimers, and many applications have been investigated, especially in the fields of materials and biology, such as thermal actuators, ionic liquids, catalysis, light harvesting systems, bioimaging, optoelectronics and drug delivery …”

“…Normally, in the molecular structure of JDs, the hydrophilic dendron is composed of poly(ethylene glycol), amino, hydroxyl and carboxyl groups, while the hydrophobic part is often constructed of aliphatic chains with different length, poly(benzyl ether) and so on. However, there are few reports on the synthesis and functional applications of Janus metallodendrimers . Metallomacromolecules, also named metal‐containing macromolecules and organometallic macromolecules, include linear metallopolymers and branched metallodendrimers, and are one of the major classes of macromolecules discovered in the twentieth century .…”

Brief Timelapse on Dendrimer Chemistry: Advances, Limitations, and Expectations

“…Diederich's group synthesized two different dendrons bearing ferrocenyl moieties at periphery, and iodoaryl and phenylacetylene groups at the focal point, respectively. An asymmetrical ferrocenyl dendrimer was obtained by connecting the two different ferrocenyl dendrons through Sonogashira reaction . One of the dendrons bear ethynylferrocenyl moieties that underwent [2 + 2] cycloaddition‐retrocyclization with tetracyanoethene, yielding a Janus dendrimer with donor–acceptor moieties.…”

“…One of the dendrons bear ethynylferrocenyl moieties that underwent [2 + 2] cycloaddition‐retrocyclization with tetracyanoethene, yielding a Janus dendrimer with donor–acceptor moieties. Based on the studies carried out on this Janus dendrimer, the authors suggest that electronic communication along the π‐system with several meta ‐connectivities is not efficient since the oxidation potential of the ferrocenyl donors on one hemisphere was not perturbed by the push‐pull acceptors on the other hemisphere …”