A single-stranded coordination copolymer affords heterostructure observation and photoluminescence intensification

Few artificial systems can be exfoliated into, and observed as, single wires with lengths of more than several micrometers, and no previous example features a copolymer structure; this is in contrast with biopolymers such as single-strand DNAs. Here, we create a set of one-dimensional coordination copolymers featuring bis(dipyrrinato)zinc complex motifs in the main chain. A series of random copolymers is synthesized from two types of bridging dipyrrin proligand and zinc acetate, with various molar ratios between the proligands. Sonication of the bulk solid copolymer in organic solvent exfoliates single strands with lengths of 1.4 to 3.0 μm. Atomic force microscopy at ambient conditions visualizes the copolymer structure as height distributions. The copolymer structure improves its photoluminescence (up to 32%) relative to that of the corresponding homopolymers (3 and 10%). Numerical simulation based on a restricted random walk model reproduces the photoluminescence intensification, suggesting at the same time the existence of fast intrawire exciton hopping.

High Electrical Conductivity of Single Metal-Organic Chains

Molecular wires are essential components for future nanoscale electronics. However, the preparation of individual long conductive molecules is still a challenge. MMX metal-organic polymers are quasi-1D sequences of single halide atoms (X) bridging subunits with two metal ions (MM) connected by organic ligands. They are excellent electrical conductors as bulk macroscopic crystals and as nanoribbons. However, according to theoretical calculations, the electrical conductance found in the experiments should be even higher. Here, a novel and simple drop-casting procedure to isolate bundles of few to single MMX chains is demonstrated. Furthermore, an exponential dependence of the electrical resistance of one or two MMX chains as a function of their length that does not agree with predictions based on their theoretical band structure is reported. This dependence is attributed to strong Anderson localization originated by structural defects. Theoretical modeling confirms that the current is limited by structural defects, mainly vacancies of iodine atoms, through which the current is constrained to flow. Nevertheless, measurable electrical transport along distances beyond 250 nm surpasses that of all other molecular wires reported so far. This work places in perspective the role of defects in 1D wires and their importance for molecular electronics.

Bis(dipyrrinato)zinc(II) Complex Chiroptical Wires: Exfoliation into Single Strands and Intensification of Circularly Polarized Luminescence

One-dimensional (1D) coordination polymers (CPs) experiences limitations in exfoliation into individual strands, which hamper their utility as functional 1D nanomaterials. Here we synthesize chiral 1D-CPs that feature the bis(dipyrrinato)zinc(II) complex motif. They can be exfoliated into single strands upon sonication in organic media, retaining lengths of up to 3.19 μm (ca. 2600 monomer units). Their chiroptical structure allows the exfoliated wires to show circularly polarized luminescence at an intensity 5.9 times that of reference monomer complexes.

Predominance of covalency in water-vapor-responsive MMX-type chain complexes revealed by (129)I Mössbauer spectroscopy

(129)I Mössbauer spectroscopy was applied to water-vapor-responsive MMX-type quasi-one-dimensional iodide-bridged Pt complexes (MMX chains) in order to investigate their electronic state quantitatively. Two sets of octuplets observed in K2(H3NC3H6NH3)[Pt2(pop)4I]·4H2O (2·4H2O) and one octuplet observed in K2(cis-H3NCH2CH=CHCH2NH3)[Pt2(pop)4I]·4H2O (1·4H2O) and dehydrated complexes (1 and 2) indicate a unique alternating charge-polarization + charge-density-wave (ACP + CDW) electronic state and a charge-density-wave (CDW) electronic state, respectively. These spectra correspond to their crystal structure and the change of electronic states upon dehydration. Since these complexes consist of an alternating array of positively charged and negatively charged layers, the charge on the iodide ion (ρIS) was discussed on the basis of the isomer shift (IS). The ρIS of the water-vapor-responsive MMX chains was mainly -0.13 to -0.21, which are the smallest of all MMX chains reported so far. Hence, it indicates that the negative charge on the iodide ion is strongly donated to the Pt ion in these complexes. This covalent interaction predominates in the ACP + CDW state as well as in the CDW state. Therefore, the ACP + CDW state is in fact the CDW state with the ACP-type lattice distortion. Because the ρIS became smaller with the decreasing Pt-I-Pt distance, it can be concluded that the covalent interaction plays an important role in determining the electronic states of the MMX chains with pop (= P2H2O5(2-)) ligands.