Design Rules for Obtaining Narrow Luminescence from Semiconductors Made in Solution.

Solution-processed semiconductors are in demand for present and next-generation optoelectronic technologies ranging from displays to quantum light sources because of their scalability and ease of integration into devices with diverse form factors. One of the central requirements for semiconductors used in these applications is a narrow photoluminescence (PL) line width. Narrow emission line widths are needed to ensure both color and single-photon purity, raising the question of what design rules are needed to obtain narrow emission from semiconductors made in solution. In this review, we first examine the requirements for colloidal emitters for a variety of applications including light-emitting diodes, photodetectors, lasers, and quantum information science. Next, we will delve into the sources of spectral broadening, including "homogeneous" broadening from dynamical broadening mechanisms in single-particle spectra, heterogeneous broadening from static structural differences in ensemble spectra, and spectral diffusion. Then, we compare the current state of the art in terms of emission line width for a variety of colloidal materials including II-VI quantum dots (QDs) and nanoplatelets, III-V QDs, alloyed QDs, metal-halide perovskites including nanocrystals and 2D structures, doped nanocrystals, and, finally, as a point of comparison, organic molecules. We end with some conclusions and connections, including an outline of promising paths forward.

Reductive dimerization of benzothiazolium salts.

Three different types of reaction products were obtained from the reduction of 2-substituted 3-methylbenzothiazolium salts using Na : Hg (1 wt%). Depending on the 2-substituents, two types of dimeric compounds were obtained: the 2-cyclohexyl-, 2-phenyl-, and 2-(p-tolyl)-substituted species are reduced to the corresponding 2,2'-bibenzo[d]thiazoles, while their 2-((p-OMe)C6H4)- and 2-((p-NMe2)C6H4)-substituted derivatives afford cis-[1,4]benzothiazino[3,2-b][1,4]benzothiazines. Furthermore, in the presence of molecular O2, new disulfide derivatives were obtained from the bibenzo[d]thiazoles. The products were obtained in a moderate to good yield, and the structures were confirmed using single-crystal X-ray diffraction. The electrochemistry and further reactivity towards different oxidants of the dimeric compounds were studied; the 2,2'-bibenzo[d]thiazoles show oxidation potentials similar to that of ferrocene and are converted back to the corresponding benzothiazolium cations by mild oxidants such as TCNQ. In contrast, the benzothiazino-benzothiazines show no oxidations in the solvent window of THF.

Thermal Properties of Polymer Hole-Transport Layers Influence the Efficiency Roll-off and Stability of Perovskite Light-Emitting Diodes.

While the performance of metal halide perovskite light-emitting diodes (PeLEDs) has rapidly improved in recent years, their stability remains a bottleneck to commercial realization. Here, we show that the thermal stability of polymer hole-transport layers (HTLs) used in PeLEDs represents an important factor influencing the external quantum efficiency (EQE) roll-off and device lifetime. We demonstrate a reduced EQE roll-off, a higher breakdown current density of approximately 6 A cm-2, a maximum radiance of 760 W sr-1 m-2, and a longer device lifetime for PeLEDs using polymer HTLs with high glass-transition temperatures. Furthermore, for devices driven by nanosecond electrical pulses, a record high radiance of 1.23 MW sr-1 m-2 and an EQE of approximately 1.92% at 14.6 kA cm-2 are achieved. Thermally stable polymer HTLs enable stable operation of PeLEDs that can sustain more than 11.7 million electrical pulses at 1 kA cm-2 before device failure.

Synthesis, Hole Doping, and Electrical Properties of a Semiconducting Azatriangulene-Based Covalent Organic Framework.

Two-dimensional covalent organic frameworks (2D COFs) containing heterotriangulenes have been theoretically identified as semiconductors with tunable, Dirac-cone-like band structures, which are expected to afford high charge-carrier mobilities ideal for next-generation flexible electronics. However, few bulk syntheses of these materials have been reported, and existing synthetic methods provide limited control of network purity and morphology. Here, we report transimination reactions between benzophenone-imine-protected azatriangulenes (OTPA) and benzodithiophene dialdehydes (BDT), which afforded a new semiconducting COF network, OTPA-BDT. The COFs were prepared as both polycrystalline powders and thin films with controlled crystallite orientation. The azatriangulene nodes are readily oxidized to stable radical cations upon exposure to an appropriate p-type dopant, tris(4-bromophenyl)ammoniumyl hexachloroantimonate, after which the network's crystallinity and orientation are maintained. Oriented, hole-doped OTPA-BDT COF films exhibit electrical conductivities of up to 1.2 × 10-1 S cm-1, which are among the highest reported for imine-linked 2D COFs to date.

Electronic Spin Qubit Candidates Arrayed within Layered Two-Dimensional Polymers.

Molecular electronic spin qubits are promising candidates for quantum information science applications because they can be reliably produced and engineered via chemical design. Embedding electronic spin qubits within two-dimensional polymers (2DPs) offers the possibility to systematically engineer inter-qubit interactions while maintaining long coherence times, both of which are prerequisites to their technological utility. Here, we introduce electronic spin qubits into a diamagnetic 2DP by n-doping naphthalene diimide subunits with varying amounts of CoCp2 and analyze their spin densities by quantitative electronic paramagnetic resonance spectroscopy. Low spin densities (e.g., 6.0 × 1012 spins mm-3) enable lengthy spin-lattice (T1) and spin-spin relaxation (T2) times across a range of temperatures, ranging from T1 values of 164 ms at 10 K to 30.2 µs at 296 K and T2 values of 2.36 µs at 10 K to 0.49 µs at 296 K for the lowest spin density sample examined. Higher spin densities and temperatures were both found to diminish T1 times, which we attribute to detrimental cross-relaxation from spin-spin dipolar interactions and spin-phonon coupling, respectively. Higher spin densities decreased T2 times and modulated the T2 temperature dependence. We attribute these differences to the competition between hyperfine and dipolar interactions for electron spin decoherence, with the dominant interaction transitioning from the former to the latter as spin density and temperature increase. Overall, this investigation demonstrates that dispersing electronic spin qubits within layered 2DPs enables chemical control of their inter-qubit interactions and spin decoherence times.

Tuning the Surface Electron Accumulation Layer of In2 O3 by Adsorption of Molecular Electron Donors and Acceptors.

In2 O3 , an n-type semiconducting transparent transition metal oxide, possesses a surface electron accumulation layer (SEAL) resulting from downward surface band bending due to the presence of ubiquitous oxygen vacancies. Upon annealing In2 O3 in ultrahigh vacuum or in the presence of oxygen, the SEAL can be enhanced or depleted, as governed by the resulting density of oxygen vacancies at the surface. In this work, an alternative route to tune the SEAL by adsorption of strong molecular electron donors (specifically here ruthenium pentamethylcyclopentadienyl mesitylene dimer, [RuCp*mes]2 ) and acceptors (here 2,2'-(1,3,4,5,7,8-hexafluoro-2,6-naphthalene-diylidene)bis-propanedinitrile, F6 TCNNQ) is demonstrated. Starting from an electron-depleted In2 O3 surface after annealing in oxygen, the deposition of [RuCp*mes]2 restores the accumulation layer as a result of electron transfer from the donor molecules to In2 O3 , as evidenced by the observation of (partially) filled conduction sub-bands near the Fermi level via angle-resolved photoemission spectroscopy, indicating the formation of a 2D electron gas due to the SEAL. In contrast, when F6 TCNNQ is deposited on a surface annealed without oxygen, the electron accumulation layer vanishes and an upward band bending is generated at the In2 O3 surface due to electron depletion by the acceptor molecules. Hence, further opportunities to expand the application of In2 O3 in electronic devices are revealed.

Organometallic and Organic Dimers: Moderately Air-Stable, Yet Highly Reducing, n-Dopants.

ConspectusElectrical doping using redox-active molecules can increase the conductivity of organic semiconductors and lower charge-carrier injection and extraction barriers; it has application in devices such as organic and perovskite light-emitting diodes, organic and perovskite photovoltaic cells, field-effect transistors, and thermoelectric devices. Simple one-electron reductants that can act as n-dopants for a wide range of useful semiconductors must necessarily have low ionization energies and are, thus, highly sensitive toward ambient conditions, leading to challenges in their storage and handling. A number of approaches to this challenge have been developed, in which the highly reducing species is generated from a precursor or in which electron transfer is coupled in some way to a chemical reaction. Many of these approaches are relatively limited in applicability because of processing constraints, limited dopant strength, or the formation of side products.This Account discusses our work to develop relatively stable, yet highly reducing, n-dopants based on the dimers formed by some 19-electron organometallic complexes and by some organic radicals. These dimers are sufficiently inert that they can be briefly handled as solids in air but react with acceptors to release two electrons and to form two equivalents of stable monomeric cations, without formation of unwanted side products. We first discuss syntheses of such dimers, both previously reported and our own. We next turn to discuss their thermodynamic redox potentials, which depend on both the oxidation potential of the highly reducing odd-electron monomers and on the free energies of dissociation of the dimers; because trends in both these quantities depend on the monomer stability, they often more-or-less cancel, resulting in effective redox potentials for a number of the organometallic dimers that are approximately -2.0 V vs ferrocenium/ferrocene. However, variations in the dimer oxidation potential and the dissociation energies determine the mechanism through which a dimer reacts with a given acceptor in solution: in all cases dimer-to-acceptor electron transfer is followed by dimer cation cleavage and a subsequent second electron transfer from the neutral monomer to the acceptor, but examples with weak central bonds can also react through endergonic cleavage of the neutral dimer, followed by electron-transfer reactions between the resulting monomers and the acceptor. We, then, discuss the use of these dimers to dope a wide range of semiconductors through both vacuum and solution processing. In particular, we highlight the role of photoactivation in extending the reach of one of these dopants, enabling successful doping of a low-electron-affinity electron-transport material in an organic light-emitting diode. Finally, we suggest future directions for research using dimeric dopants.

Dirhodium C-H Functionalization of Hole-Transport Materials.

Hole-transport materials (HTMs) based on triarylamine derivatives play important roles in organic electronics applications including organic light-emitting diodes and perovskite solar cells. For some applications, triarylamine derivatives bearing appropriate binding groups have been used to functionalize surfaces, while others have been incorporated as side chains into polymers to manipulate the processibility of HTMs for device applications. However, only a few approaches have been used to incorporate a single surface-binding group or polymerizable group into triarylamine materials. Here, we report that Rh-carbenoid chemistry can be used to insert carboxylic esters and norbornene functional groups into sp2 C-H bonds of a simple triarylamine and a 4,4'-bis(diarylamino)biphenyl, respectively. The norbenene-functionalized monomer was polymerized by ring-opening metathesis; the electrochemical, optical, and charge-transport properties of these materials were similar to those of related materials synthesized by conventional means. This method potentially offers straightforward access to a diverse range of HTMs with different functional groups.

Surface doping of rubrene single crystals by molecular electron donors and acceptors.

The surface molecular doping of organic semiconductors can play an important role in the development of organic electronic or optoelectronic devices. Single-crystal rubrene remains a leading molecular candidate for applications in electronics due to its high hole mobility. In parallel, intensive research into the fabrication of flexible organic electronics requires the careful design of functional interfaces to enable optimal device characteristics. To this end, the present work seeks to understand the effect of surface molecular doping on the electronic band structure of rubrene single crystals. Our angle-resolved photoemission measurements reveal that the Fermi level moves in the band gap of rubrene depending on the direction of surface electron-transfer reactions with the molecular dopants, yet the valence band dispersion remains essentially unperturbed. This indicates that surface electron-transfer doping of a molecular single crystal can effectively modify the near-surface charge density, while retaining good charge-carrier mobility.

Benzoimidazolium-derived dimeric and hydride n-dopants for organic electron-transport materials: impact of substitution on structures, electrochemistry, and reactivity.

1,3-Dimethyl-2,3-dihydrobenzo[d]imidazoles, 1H, and 1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[d]imidazoles, 12, are of interest as n-dopants for organic electron-transport materials. Salts of 2-(4-(dimethylamino)phenyl)-4,7-dimethoxy-, 2-cyclohexyl-4,7-dimethoxy-, and 2-(5-(dimethylamino)thiophen-2-yl)benzo[d]imidazolium (1g-i+, respectively) have been synthesized and reduced with NaBH4 to 1gH, 1hH, and 1iH, and with Na:Hg to 1g2 and 1h2. Their electrochemistry and reactivity were compared to those derived from 2-(4-(dimethylamino)phenyl)- (1b+) and 2-cyclohexylbenzo[d]imidazolium (1e+) salts. E(1+/1•) values for 2-aryl species are less reducing than for 2-alkyl analogues, i.e., the radicals are stabilized more by aryl groups than the cations, while 4,7-dimethoxy substitution leads to more reducing E(1+/1•) values, as well as cathodic shifts in E(12•+/12) and E(1H•+/1H) values. Both the use of 3,4-dimethoxy and 2-aryl substituents accelerates the reaction of the 1H species with PC61BM. Because 2-aryl groups stabilize radicals, 1b2 and 1g2 exhibit weaker bonds than 1e2 and 1h2 and thus react with 6,13-bis(triisopropylsilylethynyl)pentacene (VII) via a "cleavage-first" pathway, while 1e2 and 1h2 react only via "electron-transfer-first". 1h2 exhibits the most cathodic E(12•+/12) value of the dimers considered here and, therefore, reacts more rapidly than any of the other dimers with VII via "electron-transfer-first". Crystal structures show rather long central C-C bonds for 1b2 (1.5899(11) and 1.6194(8) Å) and 1h2 (1.6299(13) Å).

Beyond n-dopants for organic semiconductors: use of bibenzo[d]imidazoles in UV-promoted dehalogenation reactions of organic halides.

2,2'-Bis(4-dimethylaminophenyl)- and 2,2'-dicyclohexyl-1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[d]imidazole ((N-DMBI)2 and (Cyc-DMBI)2) are quite strong reductants with effective potentials of ca. -2 V vs ferrocenium/ferrocene, yet are relatively stable to air due to the coupling of redox and bond-breaking processes. Here, we examine their use in accomplishing electron transfer-induced bond-cleavage reactions, specifically dehalogenations. The dimers reduce halides that have reduction potentials less cathodic than ca. -2 V vs ferrocenium/ferrocene, especially under UV photoexcitation (using a 365 nm LED). In the case of benzyl halides, the products are bibenzyl derivatives, whereas aryl halides are reduced to the corresponding arenes. The potentials of the halides that can be reduced in this way, quantum-chemical calculations, and steady-state and transient absorption spectroscopy suggest that UV irradiation accelerates the reactions via cleavage of the dimers to the corresponding radical monomers.

Delayed Luminescence in 2-Methyl-5-(penta(9-carbazolyl)phenyl)-1,3,4-oxadiazole Derivatives.

2,5-Diphenyl-1,3,4-oxadiazole has been widely used as an acceptor portion of donor-acceptor fluorophores that exhibit thermally activated delayed fluorescence (TADF), but analogous 2-alkyl-5-phenyl-1,3,4-oxadiazoles have been much less widely investigated. Here the properties of carbazole-substituted 2-methyl-5-phenyl-1,3,4-oxadiazoles are compared to those of their 2,5-diphenyl analogues. The fluorescence of each of the former compounds is blue-shifted by ca. 50-100 meV relative to that in the latter, while similar estimated values of the singlet-triplet energy separation (ΔEST) are maintained. In particular, 2-methyl-5-(penta(9-carbazolyl)phenyl)-1,3,4-oxadiazole and 2-methyl-5-(penta(3,6-di-tert-butyl-9-carbazolyl)phenyl)-1,3,4-oxadiazole exhibit solution fluorescence maxima of 466 and 485 nm and estimated ΔEST values of 0.12 and 0.03 eV, respectively. In both cases the reverse intersystem crossing (RISC) rates inferred from their solution fluorescence behavior are over twice those of the corresponding 2-phenyl derivatives. Organic light-emitting diodes (OLEDs) in which the 2-methyl derivatives are used as emitters yield external quantum efficiency (EQE) values of up to 23%. OLEDs with 2-methyl-5-(penta(9-carbazolyl)phenyl)-1,3,4-oxadiazole and 2-methyl-5-(penta(3,6-di-tert-butyl-9-carbazolyl)phenyl)-1,3,4-oxadiazole emitters show reduced efficiency rolloff at high current densities relative to their 2-phenyl counterparts, the latter exhibiting an EQE of 16% at 1000 cd m-2.

Synthetic Routes for Heteroatom-Containing Alkylated/Arylated Polycyclic Aromatic Hydrocarbons.

Synthetic routes for heteroatom-containing polycyclic aromatic hydrocarbons (H-PAHs) with alkyl and aryl substitution are demonstrated. Three H-PAHs, including heteroatom-containing rubicenes (H-rubicenes), angular-benzothiophenes (ABTs), and indenothiophene (IDTs) were successfully synthesized by two key steps, including polysubstituted olefin formation and cyclization. Specifically, ABT and H-rubicenes were comprehensively investigated by single-crystal X-ray diffraction, NMR spectroscopy, UV-vis absorption, cyclic voltammetry, transient absorption, and single-crystal OFET measurements.

New Mechanistic Insights into the Formation of Imine-Linked Two-Dimensional Covalent Organic Frameworks.

A more robust mechanistic understanding of imine-linked two-dimensional covalent organic frameworks (2D COFs) is needed to improve their crystalline domain sizes and to control their morphology, both of which are necessary to fully realize their application potential. Here, we present evidence that 2D imine-linked COFs rapidly polymerize as crystalline sheets that subsequently reorganize to form stacked structures. Primarily, this study focuses on the first few minutes of 1,3,5-tris(4-aminophenyl)benzene and terephthaldehyde polymerization, which yields an imine-linked 2D COF. In situ X-ray diffraction and thorough characterization of solids obtained using gentler isolation and activation methods than have typically been used in the literature indicate that periodic imine-linked 2D structures form within 60 s, which then form more ordered stacked structures over the course of several hours. This stacking process imparts improved stability toward the isolation process relative to that of the early stage materials, which likely obfuscated previous mechanistic conclusions regarding 2D polymerization that were based on products isolated using harsh activation methods. This revised mechanistic picture has useful implications; the 2D COF layers isolated at very short reaction times are easily exfoliated, as observed in this work using high-resolution transmission electron microscopy and atomic force microscopy. These results suggest improved control of imine-linked 2D COF formation can be obtained through manipulation of the polymerization conditions and interlayer interactions. Qualitatively similar results were obtained for analogous materials obtained from 2,5-di(alkoxy)terephthaldehyde derivatives, except for the COF with the longest alkoxy chains examined (OC12H25), which, although shown by in situ X-ray diffraction to be highly crystalline in the reaction mixture, is much less crystalline when isolated than the other COFs examined, likely due to the more severe steric impact of the dodecyloxy functionality on the stacking process.

Electronically Coupled 2D Polymer/MoS2 Heterostructures.

Emergent quantum phenomena in electronically coupled two-dimensional heterostructures are central to next-generation optical, electronic, and quantum information applications. Tailoring electronic band gaps in coupled heterostructures would permit control of such phenomena and is the subject of significant research interest. Two-dimensional polymers (2DPs) offer a compelling route to tailored band structures through the selection of molecular constituents. However, despite the promise of synthetic flexibility and electronic design, fabrication of 2DPs that form electronically coupled 2D heterostructures remains an outstanding challenge. Here, we report the rational design and optimized synthesis of electronically coupled semiconducting 2DP/2D transition metal dichalcogenide van der Waals heterostructures, demonstrate direct exfoliation of the highly crystalline and oriented 2DP films down to a few nanometers, and present the first thickness-dependent study of 2DP/MoS2 heterostructures. Control over the 2DP layers reveals enhancement of the 2DP photoluminescence by two orders of magnitude in ultrathin sheets and an unexpected thickness-dependent modulation of the ultrafast excited state dynamics in the 2DP/MoS2 heterostructure. These results provide fundamental insight into the electronic structure of 2DPs and present a route to tune emergent quantum phenomena in 2DP hybrid van der Waals heterostructures.

Humidity Sensing through Reversible Isomerization of a Covalent Organic Framework.

Here we report that a covalent organic framework (COF), which contains 2,5-di(imine)-substituted 1,4-dihydroxybenzene (diiminol) moieties, undergoes color changes in the presence of solvents or solvent vapor that are rapid, passive, reversible, and easily detectable by the naked eye. A new visible absorption band appears in the presence of polar solvents, especially water, suggesting reversible conversion to another species. This reversibility is attributed to the ability of the diiminol to rapidly tautomerize to an iminol/cis-ketoenamine and its inability to doubly tautomerize to a diketoenamine. Density functional theory (DFT) calculations suggest similar energies for the two tautomers in the presence of water, but the diiminol is much more stable in its absence. Time-dependent DFT calculations confirm that the iminol/cis-ketoenamine absorbs at longer wavelength than the diiminol and indicate that this absorption has significant charge-transfer character. A colorimetric humidity sensing device constructed from an oriented thin film of the COF responded quickly to water vapor and was stable for months. These results suggest that tautomerization-induced electronic structure changes can be exploited in COF platforms to give rapid, reversible sensing in systems that exhibit long-term stability.

Double doping of conjugated polymers with monomer molecular dopants.

Molecular doping is a crucial tool for controlling the charge-carrier concentration in organic semiconductors. Each dopant molecule is commonly thought to give rise to only one polaron, leading to a maximum of one donor:acceptor charge-transfer complex and hence an ionization efficiency of 100%. However, this theoretical limit is rarely achieved because of incomplete charge transfer and the presence of unreacted dopant. Here, we establish that common p-dopants can in fact accept two electrons per molecule from conjugated polymers with a low ionization energy. Each dopant molecule participates in two charge-transfer events, leading to the formation of dopant dianions and an ionization efficiency of up to 200%. Furthermore, we show that the resulting integer charge-transfer complex can dissociate with an efficiency of up to 170%. The concept of double doping introduced here may allow the dopant fraction required to optimize charge conduction to be halved.

Surface Functionalization of Black Phosphorus with a Highly Reducing Organoruthenium Complex: Interface Properties and Enhanced Photoresponsivity of Photodetectors.

In this work, a heterostructure obtained by vacuum evaporation of a strong molecular n-dopant, [RuCp*(mes)]2 , onto black phosphorus (BP) is reported, along with the systematic investigation of the interfacial structure and properties by various in situ characterization techniques. Ultraviolet photoelectron spectra (UPS) showed a large decrease in the work function of BP and a new peak within the bandgap, which is attributed to electron transfer from dopants to the underlying BP. The electrons trapped at the interface act as hole traps and induce photogating effect so that a photodetector based on BP-organoruthenium complex heterostructure demonstrates a photoresponsivity of 5.5 mA W-1 and an EQE of 1.3 % at 515 nm, a tenfold improvement compared to the pristine BP device.

Potential-Modulated Total Internal Reflection Fluorescence for Measurement of the Electron Transfer Kinetics of Submonolayers on Optically Transparent Electrodes.

An electroreflectance method to determine the electron transfer rate constant of a film of redox-active chromophores immobilized on an optically transparent electrode when the surface coverage of the film is very low (<0.1 monolayer) is described herein. The method, potential-modulated total internal reflection fluorescence (PM-TIRF) spectroscopy, is a fluorescence version of potential-modulated attenuated total reflection (PM-ATR) spectroscopy that is applicable when the immobilized chromophores are luminescent. The method was tested using perylene diimide (PDI) molecules functionalized with p-phenylene phosphonic acid (PA) moieties that bind strongly to indium-tin oxide (ITO). Conditions to prepare PDI-phenyl-PA films that exhibit absorbance and fluorescence spectra characteristic of monomeric (i.e., nonaggregated) molecules were identified; the electrochemical surface coverage was approximately 0.03 monolayer. The tilt angle of the long axis of the PDI molecular plane is 58° relative to the ITO surface normal, 25° greater than the tilt angle of aggregated PDI-phenyl-PA films, which have a surface coverage of approximately one monolayer. The more in-plane orientation of monomeric films is likely due to the absence of cofacial π-π interactions present in aggregated films and possibly a difference in PA-ITO binding modes. The electron transfer rate constant (ks,opt) of monomeric PDI-phenyl-PA films was determined using PM-TIRF and compared with PM-ATR results obtained for aggregated films. For PDI monomers, ks,opt = 3.8 × 103 s-1, which is about 3.7-fold less than ks,opt for aggregated films. The slower kinetics are attributed to the absence of electron self-exchange between monomeric PDI molecules. Differences in the electroactivity of the binding sites on the ITO electrode surface also may play a role. This is the first demonstration of PM-TIRF for determining electron transfer rate constants at an electrode/organic film interface.

Structural Diversity in 2,2'-[Naphthalene-1,8:4,5-bis(dicarboximide)-N,N'-diyl]-bis(ethylammonium) Iodoplumbates.

Crystallization from solutions containing 2,2'-[naphthalene-1,8:4,5-bis(dicarboximide)-N,N'-diyl]-bis(ethylammonium) diiodide ((NDIC2)I2) and PbI2 has been investigated. Eight different materials are obtained, either by variation of crystallization conditions or by subsequent thermal or solvent-induced transformations. Crystal structures have been determined for five materials. [(NDIC2)2Pb5I14(DMF)2]·4DMF (DMF = N,N-dimethylformamide) (1), [(NDIC2)Pb4I10]·4DMF (3), [(NDIC2)Pb2I6]·4NMP (NMP = N-methyl-2-pyrrolidone) (4), and [(NDIC2)Pb2I6]·2H2O (5) form 1-dimensional (1D) chains consisting of PbI6 (and, in the case of 1, PbI5(DMF)) octahedra, either solely face-sharing or a mixture of face-sharing and vertex-sharing. The structure of [(NDIC2)3Pb5I16]·6NMP (2) contains 0D clusters; these consist of three PbI6 octahedra and two unusually coordinated lead centers that exhibit three relatively short Pb-I bonds, two very long Pb-I contacts, and η2-coordination of an aromatic ring of NDIC2 to the lead. Close contacts between iodide ions and the imide rings of NDIC2 in four of the structures suggest that an iodide-to-NDIC2 charge-transfer interaction may be responsible for the observed red coloration of the materials. The optical and electrical properties of 1 have been studied; its onset of absorption is at 2.0 eV, and its conductivity was measured as 5.4 × 10-5 ± 1.1 × 10-5 S m-1.