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We report a computational and experimental study of the reaction of oxadiazinones and strained alkynes to give polycyclic aromatic hydrocarbons (PAHs). The reaction proceeds by way of a pericyclic reaction cascade and leads to the formation of four new carbon-carbon bonds. Using M06-2X DFT calculations, we interrogate several mechanistic aspects of the reaction, such as why the use of non-aromatic strained alkynes can be used to access unsymmetrical PAHs, whereas the use of arynes in the methodology leads to symmetrical PAHs. In addition, experimental studies enable the rapid synthesis of new PAHs, including tetracene and pentacene scaffolds. These studies not only provide fundamental insight regarding the aforementioned cycloaddition cascades and synthetic access to PAH scaffolds, but are also expected to enable the synthesis of new materials.

5,11-Diazadibenzo[hi,qr]tetracene was synthesized as a new nitrogen-substituted polycyclic heteroaromatic compound by Pd-catalyzed cycloisomerization of an alkyne precursor followed by oxidative cyclization with bis(trifluoroacetoxy)iodobenzene. The substitution of imine-type nitrogen atoms significantly enhanced its electron-accepting character and facilitated the direct nucleophilic addition of arylamines under strongly basic conditions to afford the desired amino-substituted products. The introduction of amino groups induced a remarkable red-shift in their absorption spectra; the tetrasubstituted product exhibited intense near-infrared absorbing property. Furthermore, the π-electronic system, which includes a redox-active 1,4-diazabutadiene moiety, underwent reversible interconversion to its corresponding reduced form upon reduction with NaBH4 and aerobic oxidation.

The operating temperature of PV modules affects the rate of degradation. We show the extent to which module operating temperature can be reduced by increasing the efficiency of the PV module via a tandem architecture or singlet Fission, the latter being of interest as a potentially endothermic process. PV modules that employ tetracene as a singlet fission material are found to be resilient against degradation since the degradation product is transparent to solar radiation.

A unified low-temperature reaction mechanism on the formation of acenes, phenacenes, and helicenes-polycyclic aromatic hydrocarbons (PAHs) that are distinct via the linear, zigzag, and ortho-condensed arrangements of fused benzene rings-is revealed. This mechanism is mediated through a barrierless, vinylacetylene mediated gas-phase chemistry utilizing tetracene, [4]phenacene, and [4]helicene as benchmarks contesting established ideas that molecular mass growth processes to PAHs transpire at elevated temperatures. This mechanism opens up an isomer-selective route to aromatic structures involving submerged reaction barriers, resonantly stabilized free-radical intermediates, and systematic ring annulation potentially yielding molecular wires along with racemic mixtures of helicenes in deep space. Connecting helicene templates to the Origins of Life ultimately changes our hypothesis on interstellar carbon chemistry.

Singlet fission has emerged as a promising strategy to avoid the loss of extra energy through thermalization in solar cells. A family of dimers consisting of nitrogen‐doped pyrene‐fused acenes that undergo singlet fission with triplet quantum yields as high as 125 % are presented. They provide new perspectives for nitrogenated polycyclic aromatic hydrocarbons and for the design of new materials for singlet fission., Come Together: By introducing dibenzodiazahexacene moieties in a dimeric architecture, a new type of singlet fission material was obtained. Solvent‐dependent triplet quantum yields of up to 125 % were achieved.

5,12-Diamino-substituted tetracenes with various N-substituents have been prepared, and their molecular structural changes upon oxidation have been evaluated in association with their electronic structures. The N-substituents influence both the electronic and molecular structures of the oxidized species of 5,12-diaminotetracenes. The tetracene moiety of 5,12-bis(N,N-dianisylamino)tetracene retained its planarity during the course of two successive one-electron oxidations, whereas 5,12-bis(N,N-dimethylamino)tetracene and 5,12-bis(N-anisyl-N-methylamino)tetracene underwent substantial structural changes into butterfly like structures through a simultaneous two-electron oxidation process. The molecular structures in the oxidized states were closely related to the nature of the highest occupied orbitals, which were characterized by the extent of mixing between the fragment orbitals for the teracene moiety and the substituted amino groups in 5,12-diaminotetracenes. As a consequence, the present work revealed that the extent of folding deformation of the acene moiety in the oxidized diaminoacenes could be fine-tuned by varying the N-substituents.

A set of flapping acene dimers fused with an 8π cyclooctatetraene (COT) ring showed distinct excited-state dynamics in solution. While the anthracene dimer showed a fast V-shaped-to-planar conformational change within 10 ps in the lowest excited singlet state, reminding us of extended Baird aromaticity, the tetracene dimer and the pentacene dimer underwent intramolecular singlet fission (SF) in different manners: A fast and reversible SF with a characteristic delayed fluorescence (FL), and a fast and quantitative SF, respectively. Conformational flexibility of the fused COT linkage plays an important role in these ultrafast dynamics, demonstrating the utility of the flapping molecular series as a versatile platform for designing photofunctional systems.

The addition of phenyllithium to a polycyclic quinone, 9,11,12,21,22,24-hexaphenyltetrabenzo[a,c,n,p]hexacene-10,23-dione (10), followed by SnCl2 -mediated reduction of the diol intermediate, yielded 9,10,11,12,21,22,23,24-octaphenyltetrabenzo-[a,c,n,p]hexacene (4). Crystallographic analysis of hexacene 4 showed it to possess a longitudinal twist of 184°, which was in good agreement with AM1 calculations. In addition to being the most twisted acene synthesized to this point, compound 4 contains within its substructure the most twisted naphthalene, anthracene, tetracene, and pentacene moieties described.

Rationale The anion mass spectral lifetimes for several aromatic hydrocarbons reported in the subject article were related to significantly different electron affinities. The different values are rationalized using negative ion mass spectral data. Methods Electron affinities for polycyclic aromatic hydrocarbons are reported from the temperature dependence of unpublished electron capture detector data. These are compared with published values and the largest values are assigned to the ground state. Results The ground state adiabatic electron affinities: (eV) pentacene, 1.41 (3); tetracene, 1.058 (5); benz(a)pyrene, 0.82 (4); benz(a) anthracene, 0.69 (2) anthracene, 0.68 (2); and pyrene, 0.59 (1) are used to assign excited state adiabatic electron affinities: (eV) tetracene: 0.88 (4); anthracene 0.53 (1); pyrene, 0.41 (1); benz(a)anthracene, 0.39 (10); chrysene, 0.32 (1); and phenanthrene, 0.12 (2) and ground state adiabatic electron affinities: (eV) dibenz(a,j)anthracene, 0.69 (3); dibenz(a,h)anthracene, 0.68 (3); benz(e)pyrene, 0.60 (3); and picene, 0.59 (3) from experimental data. The lifetime of benz(a)pyrene is predicted to be larger than 150 μs and for benzo(c)phenanthrene and picene about 40 μs, from ground state adiabatic electron affinities. Conclusions The assignments of adiabatic electron affinities of aromatic hydrocarbons determined from electron capture detector and mass spectrometric data to ground and excited states are supported by constant electronegativities. A set of consistent ground state adiabatic electron affinities for 15 polycyclic aromatic hydrocarbons is related to lifetimes from the subject article.

Here, we observe that a sub-monolayer CdS shell on PbS quantum dots (QDs) enhances triplet energy transfer (TET) by suppressing competitive charge transfer from QDs to molecules. The CdS shell increases the linear photon upconversion quantum yield (QY) from 3.5% for PbS QDs to 5.0% for PbS/CdS QDs when functionalized with a tetracene acceptor, 5-CT. While transient absorption spectroscopy reveals that both PbS and PbS/CdS QDs show the formation of the 5-CT triplet (with rate constants of 5.91 ±0.60 ns-1 and 1.03 ±0.09 ns-1 respectively), ultrafast hole transfer occurs only from PbS QDs to 5-CT. Although the CdS shell decreases the TET rate, it enhances TET efficiency from 60.3± 6.1% to 71.8 ±6.2% by suppressing the hole transfer process. In addition, the CdS shell prolongs the lifetime of the 5-CT triplet and thus enhances TET from 5-CT to the rubrene emitter, further bolstering the upconverison QY.

The outstanding performance of pentacene-based molecules in molecular electronics, as well as the predicted enhanced semiconducting properties of extended acenes, have stimulated the development of new synthetic methods and functionalization strategies for the preparation of stable and soluble acenes larger than tetracene with the aim of obtaining improved functional materials.

By direct imaging of singlet and triplet populations with ultrafast microscopy, it is shown that the triplet diffusion length and singlet fission yield can be simultaneously optimized for tetracene and its derivatives, making them ideal structures for application in bilayer solar cells.

We observe the diffusion anisotropy difference between singlet and triplet excitons in organic crystals; that is, singlet and triplet excitons may have completely different spatial direction preference for diffusion. This phenomenon can be ascribed to the distinct dependence of different excitonic couplings (Coulomb Förster vs. exchange Dexter) existing in singlet and triplet excitons on their intermolecular distance and intermolecular orientation. Such a discovery provides insights for understanding the fundamental photophysical process in a vast range of organic condensed‐phase systems and optimizing the efficiency of organic optoelectronic materials.

Pentacene has attracted much attention as an organic electric material, but it often suffers from its very low solubility. We now report self-assembled rectangular host 18+ that has two pairs of terpyridine–PtII moieties aligned parallel to each other and connected by diyne linkers. The host encapsulated unsubstituted pentacene (2) with a remarkably strong binding constant of Ka ≈ 107 M–1 and solubilized it in acetonitrile up to the millimolar level. For smaller acenes (i.e., naphthalene to tetracene), a planar arrangement of two molecules inside the cavity was achieved. These results made it possible to analyze the acenes in the solution phase and provided a way to align the guests by a solution-processing method as a possible application, and thus, they contribute to fundamental physical organic chemistry as well as organic electronics.

A molecular Solomon link was synthesized in high yield through the template-free, coordination-driven self-assembly of a carbazole-functionalized donor and a tetracene-based dinuclear ruthenium(II) acceptor. The doubly interlocked topology was realized by a strategically chosen ligand which was capable of participating in multiple CH⋅⋅⋅π and π-π interactions, as evidenced from single-crystal X-ray analysis and computational studies. This method is the first example of a two-component self-assembly of a molecular Solomon link using a directional bonding approach. The donor alone was not responsible for the construction of the Solomon link, and was confirmed by its noncatenane self-assemblies obtained with other similar ruthenium(II) acceptors.

Multifunctional operation of tetracene/polycyclopentadithiophene-benzothiadiazole (PCPDTBT), and tetracene sensitized PCPDTBT:fullerene bulk heterojunctions (BHJs) that work as an organic photovoltaic (OPV), organic light emitting diode (OLED), and organic photodetector (OPD) is unveiled. The multifunctional operation is underlined by a synergetic interplay between singlet and triplet energy transfer and the judicious alignment of energy levels of donor-acceptor cascade. Introduction of tetracene is shown to enhance electroluminescence (EL) at 800 nm despite the observation of a near-complete photoluminescence quenching in BHJ systems. Signatures of triple energy transfer mediated via charge transfer states of BHJ to tetracene become apparent as the proportion of fullerene in the BHJ is increased. An optimal balance between exciton population is achieved with BHJ 1:2 that produces EL peaks at 530 and 800 nm while maintaining a respectable OPV and OPD performance. The proposed ternary system unlocks the potential of having multifunctionality within one single diode structure, and it also offers new design rules for multispectral OLEDs.

A four-step synthesis of substituted 5,11-dicyano-6,12-diaryltetracenes was developed, starting from readily available para-substituted benzophenones. The key step of this straightforward route is the complex cascade reaction between tetraaryl[3]cumulenes and tetracyanoethene (TCNE) resulting in 5,5,11,11-tetracyano-5,11-dihydrotetracenes. The mechanism of this transformation was reinvestigated by means of theoretical calculations. The target tetracenes were obtained by a newly developed decyanation/aromatization reaction catalyzed by CuI or CuII complexes in solution, conditions compatible with a broad range of functional groups. A computational mechanistic study sheds light on this transformation. Structures of all tetracene derivatives were confirmed by X-ray crystallography. The presented dicyanotetracene derivatives exhibit outstanding optoelectronic properties and enhanced photostability, significantly surpassing the reference rubrene (5,6,11,12-tetraphenyltetracene).

A systematic study on the regioselective cyclization of benzene- and naphthalene-based unsymmetrical diols with HBr (33 %) in acetic acid at room temperature led to the formation of annulation products. By using this method, synthesis of a wide variety of anthracene, tetracene and naphtho[b]thiophene analogues was achieved in good to excellent yields. By employing HBr (33 %) in acetic acid as a catalyst for regioselective cyclization of unsymmetrical diols was very facile and devoid of commonly encountered dihydroisobenzofuran formation.

A new approach to evaluate quantitatively the weights of local excitation (LE) and charge-transfer (CT) transition in the excited state of molecular aggregates has been proposed. It can be achieved by the combination of the molecular orbital fragmentation and natural transition orbital analysis. Armed with this method, we investigated the singlet excited state of acene molecules for representative dimer configurations, i.e., face-to-face and herringbone configurations of anthracene, tetracene, and pentacene at scaled opposite spin (SOS)–configuration interaction single (CIS(D)) level of theory. In the case of the face-to-face configuration, we found excited state wavefunctions significantly delocalized, giving rise to equal contributions from LE and CT. In the herringbone configuration, however, we found CT character of the excited state marginal. It turned out, however, that, when dimers get closer via intermolecular stretching vibration, CT admixture can be enhanced. Furthermore, in the case of heptamer, CT admixture was substantially magnified, consisting with previous report by Spano and coworkers (J. Chem. Phys. 2011, 134, 204703). Hence, the excited states of molecular aggregates can be quantum chemically analyzed via our approach and important insights into them can be obtained.

Nanocarbons are synthetic carbon-rich compounds with polyaromatic frameworks that have lately attracted attention as emerging functional materials. However, their extreme hydrophobicity and aggregation peculiarity, besides their shape and size diversities, precluded their study in solution, especially in "green" water. More convenient and general solubilizing methods of nanocarbon frameworks are required by using non-covalent supramolecular interactions. Here we report a protocol for solubilizing a wide range of nanocarbons, that is, fullerenes (C60 , C70 , C84 , and C120 ), polyarenes (tetracene, pentacene, perylene, coronene, and hexabenzocoronene), and carbon nanotubes (single-walled and multi-walled CNTs), in water through manual grinding with V-shaped polyaromatic amphiphiles. The obtained aqueous nanocomposites are composed of nanocarbons encircled by the polyaromatic frameworks of the amphiphiles through multiple aromatic-aromatic interactions. Notably, the encapsulated photosensitive nanocarbons, such as tetracene, pentacene, and fullerene dimer, exhibit unusual stability toward UV/Vis light.

Thin films of 5,11-dicyano-6,12-diphenyltetracene (TcCN) have been studied for their ability to undergo singlet exciton fission (SF). Functionalization of tetracene with cyano substituents yields a more stable chromophore with favorable energetics for exoergic SF (2E(T1)-E(S1)=-0.17 eV), where S1 and T1 are singlet and triplet excitons, respectively. As a result of tuning the triplet-state energy, SF is faster in TcCN relative to the corresponding endoergic process in tetracene. SF proceeds with two time constants in the film samples (τ=0.8±0.2 ps and τ=23±3 ps), which is attributed to structural disorder within the film giving rise to one population with a favorable interchromophore geometry, which undergoes rapid SF, and a second population in which the initially formed singlet exciton must diffuse to a site at which this favorable geometry exists. A triplet yield analysis using transient absorption spectra indicates the formation of 1.6±0.3 triplets per initial excited state.

Perylene bisimides (PBIs) are fascinating dyes with various potential applications. To study the effects of introducing a dibenzo-fused structure to the perylene moiety, π-extended PBI derivatives with a dibenzo-fused structure at both of the a and f bonds were synthesized. The twisted structure was characterized by X-ray crystal structure analysis. In the cyclic voltammograms, the dibenzo[a,f]-fused PBI showed a reversible oxidation wave at much less positive potential, relative to a dibenzo[a,o]-fused PBI derivative. These data indicated that two ring fusions at both sides of a naphthalene moiety, which construct a tetracene core, effectively raise the HOMO level compared to fusion of one ring at each naphthalene moiety (two anthracene cores). The dibenzo[a,f]-fused PBI derivative showed an absorption band at 735 nm with a shoulder band reaching 900 nm.

A simple method for electrochemical oxidation and degradation of carcinogenic tetracene (TC) to surface confined redox active quinone species (TCO) on a pris- tine-multiwalled carbon nanotube modified (MWCNT) gold electrode surface (Au/MWCNT) by applying a static potential at 0.9 V vs. Ag/AgCl in pH 7 phosphate buffer solution has been demonstrated. Various physicochemical characterizations of MWCNT@TCO by TEM, FT-IR, Raman spectroscopy and GC-MS reveal the presence of two types of redox sites, hydroquinone and anthraqui- none derivatives within the MWCNT@TCO. The modi- fied electrode showed selective electrocatalytic reduction and amperometric i-t sensing of H2O2 with a detection limit (signal-to-noise = 3) of 122 nM.

High-quality polycrystalline polyacenes (PLAs) of anthracene (AN), tetracene (TN), and pentacene (PN) doped with potassium in the 1:1 and 1:2 stoichiometries are prepared and their physical properties are systematically studied by magnetic measurements. The magnetic susceptibilities as a function of temperature for Kx(PLAs) are interpreted in the framework of a band-filling model. Clear evidence for the occurrence of charge transfer from K to the organic semiconductors is provided. K1(AN) prepared by a solid-state diffusion process exhibits a pronounced magnetic hump at 140 K, which is associated with antiferromagnetic interactions ascribed to the on-site Coulomb repulsion in a Mott insulating state, whereas both K1(TN) and K1(PN) show a conventional Curie–Weiss behavior at low temperatures. We successfully demonstrate the tuning of the electronic states of PLA-type semiconductors in bulk. Comments are given about the possibility of metallic states in potassium-doped PLAs, which have recently been reported for other polycyclic aromatic hydrocarbons.

The astounding electronic performance of acenes such as tetracene and pentacene (and their heteroaromatic counterparts) stands to revolutionize the field of organic electronics, promising novel consumer electronics for power generation and information display in lightweight, flexible form factors. These results have rekindled interest in acenes larger than pentacene, to determine how electronic properties are further altered by extending conjugation. This research has had to encompass many fundamental studies, as even the simple nature of aromaticity in larger acenes is still a controversial topic. Further, the reactivity of acenes toward oligomerization or oxidation becomes significant in larger acenes, while the diminishing solubility complicates isolation and characterization. This article surveys recent works describing the nature of aromaticity and reactivity in larger acenes, methods used to prepare parent acenes larger than pentacene, and functionalization approaches to soluble, reasonably stable large acenes.

A versatile, two-step synthesis of highly substituted, cyano-functionalized diaryltetracenes has been developed, starting from easily accessible tetraaryl[3]cumulenes. This unprecedented transformation is initiated by [2+2] cycloaddition of tetracyanoethylene (TCNE) to the proacetylenic central double bond of the cumulenes to give an intermediate zwitterion, which after an electrocyclization cascade and dehydrogenation yields 5,5,11,11-tetracyano-5,11-dihydrotetracenes in a one-pot procedure. A subsequent copper-assisted decyanation/aromatization provided the target 5,11-dicyano-6,12-diaryltetracene derivatives. All of the postulated structures were confirmed by X-ray crystallography. The new chromophores are thermally highly stable and feature promising fluorescence properties for potential use in optoelectronic devices. They are selective chemosensors for Cu(I) ions, which coordinate to one of the CN substituents and form a 1:1 complex with an association constant of Ka =1.5×10(5) L mol(-1) at 298 K.

Aggregation processes that occur in a solution of 3.4 × 10−5 M tetracene in decalin at 213 K and in a 1.3 × 10−4 M solution of anthracene in methylcyclohexane at 135 K show that they are second-order kinetic processes responsible for generating the corresponding dimeric structures of these acenes. The UV–Vis absorption spectra of these dimeric structures show the presence of isosbestic points. We also show that the rate constants of these processes appear to depend on the viscosity of the solvent employed. Excitonic interactions involved in these dimers are described in the light of Kasha's model. We also show that a solution of 6.7 × 10−5 of tetracene in toluene at 173 K exhibits aggregation but following a first order kinetics and that the corresponding absorption spectra describing the process at 173 K show no isosbestic points. Consequently, it is concluded that in this solvent, the tetracene does not dimerize, but it forms a complex with toluene. The strong similarity between the first band of the tetracene dimer and the tetracene/toluene complex may give rise to a strong controversy over the excitonic model to be considered. Copyright © 2014 John Wiley & Sons, Ltd.

The synthesis of tetracene- and pentacene-annulated norbornadienes, formed through the Diels-Alder reaction of a dehydroacene with cyclopentadiene is reported. Ring-opening metathesis polymerization (ROMP) leads to polymers that are investigated with respect to their physical, optical, and electronic properties by gel permeation chromatography (GPC), UV-vis spectroscopy, and cyclic voltammetry. The pentacene-containing polymer P1 is successfully integrated into an organic field-effect transistor (OFET); the tetracene-containing polymer P2 is integrated into an organic light-emitting diode (OLED).

In this account, the synthesis and applications of pyrene-fused acenes, as well as pyrene-fused azaacenes, have been carefully reviewed. Moreover, the synthetic methods involving two key synthons (different lengths of dienes and ynes) have been included. Furthermore, the "clean reaction" strategy has been introduced for the preparation of pyrene-fused acenes with a single terminal-pyrene unit from tetracene to octacene, as well as for the synthesis of pyrene-fused octatwistacenes and nonatwistacenes with double terminal-pyrene units. Similarly, the synthons and the synthetic methods for pyrene-fused azaacenes have also been summarized. The applications of pyrene-fused acenes and pyrene-fused azaacenes have been included.

Unsymmetrical 5,12-diethynyltetracene derivatives were synthesized from tetracenequinone by the addition of two types of ethynyllithium reagents, followed by reductive aromatization with SnCl2­. These three-step reactions could be integrated into a one-pot process to give unsymmetrically substituted 5,12-diethynyltetracene derivatives in moderate yields. Some unsymmetrical 5,12-bis(phenylethynyl)tetracene derivatives were synthesized from 5-ethynyl-12-phenylethynyltetracene and iodobenzenes by Sonogashira coupling. This integrated process was applied to the synthesis of a π-extended tetracene dimer. The photophysical properties of these compounds were examined by UV/Vis and fluorescence spectroscopy.

A systematic study on the regioselective cyclization of benzene- and naphthalene-based unsymmetrical diols with HBr (33 %) in acetic acid at room temperature led to the formation of annulation products. By using this method, synthesis of a wide variety of anthracene, tetracene and naphtho[b]thiophene analogues was achieved in good to excellent yields. By employing HBr (33 %) in acetic acid as a catalyst for regioselective cyclization of unsymmetrical diols was very facile and devoid of commonly encountered dihydroisobenzofuran formation.

In the solution state, there were no notable differences between the optical properties of a range of alkyl-substituted tetracenes. However, in the solid state, their photophysical properties changed with respect to the length, shape, number, and substitution pattern of the alkyl side chains, as well as the distribution of two regioisomers. Remarkably, in the solid state, 1,4,7,10-tetraisopropyltetracene exhibited the highest reported fluorescence quantum yield of any tetracene derivative (0.90). The changes in the optical characteristics of these tetracenes according to the arrangement of the tetracene rings and the color-change mechanism in the solid state are discussed. Moreover, the world record in solid-state fluorescence efficiency in acenes larger than anthracene is described. DOI 10.1002/tcr.201200003

Mono-, di- and tetraanions of rubrene, (C42H28, Rub0), were generated by the controlled reduction of neutral polyarene with various alkali metals in the appropriate solvent. The X-ray diffraction studies of the resulting adducts of Rub1–, Rub2– and Rub4– with alkali-metal ions revealed the distortion of the rubrene core upon the stepwise acquisition of electrons. Coordination of the Cs+ ion and a noticeable deformation of Rub1– are observed at the first reduction step. Two types of rubrene dianions showing an essentially different conformation and coordination environment for the central tetracene core have been seen in the cesium adduct of Rub2–. Various types of supramolecular assembly between the tetrareduced rubrene anion, Rub4–, and lithium or rubidium cations have been found in the corresponding products in the solid state. The structures of rubrene anions and their aggregation with alkali-metal ions in solution have been studied by ESR and multinuclear NMR (1H, 13C, 7Li and 133Cs) spectroscopy.

High-efficiency fullerene-free single-heterojunction (SHJ) organic photovoltaic (OPV) cells consisting of tetracene (Tc) as a typical donor material and boron subphthalocyanine chloride (SubPc) as an acceptor material are reported. Cells containing SubPc as a direct replacement for C60 exhibit an ∼60% improvement in open circuit voltage (Voc) achieving a maximum Voc of 1.24 V, which is amongst the highest values acheived to date for SHJ devices. This resulted in an overall improvement of ∼60% in power conversion efficiency from 1.8%, for Tc/C60 cells, to 2.9% for Tc/SubPc. The OPV device results are complemented by soft X–ray photoelectron spectroscopy (PES) measurements of the interfacial energetics of both systems. The results demonstrate that SubPc shows considerable promise as an electron acceptor material for future cell designs.

The electronic spectra in the 32-4 kK region of the mononegative ions of naphthalene, anthracene, tetracene, phenanthrene, diphenyl, terphenyl, quaterphenyl, pyrene, perylene, triphenylene and coronene are given. The spectra of the dinegative ions of anthracene, tetracene, terphenyl, quaterphenyl and perylene have also been investigated.

A study was made of the photoconductivity of anthracene crystals containing small amounts of tetracene and acridine in the crystal lattice and with aqueous solutions as the electrode material. Doping of anthracene with tetracene markedly reduced the photoconductivity but increased the variation of the photocurrent with the wavelength of the exciting light. The photoconductivity spectrum of heavily doped crystals accurately duplicated the absorption spectrum of anthracene. The theory according to which charge carriers in anthracene are generated only at the positive crystal-water interface and the role of tetracene as a trap for excitation energy in anthracene can adequately explain the effects of tetracene on the photoconductivity. The effects of acridine on the photoconductivity of anthracene were opposite to those of tetracene. In order to understand the latter results another or an additional mechanism for the generation of charge carriers must be assumed to exist in the crystals doped with acridine.

The electronic spectra of the mononegative ions of naphthalene, anthracene, tetracene, phenanthrene, pyrene, perylene, biphenyl, terphenyl and quater-phenyl have been qualitatively interpreted with the aid of L.C.A.O.-M.O. calculations including configuration interaction. The calculated dipole strengths are on the average about twice to three times as high as the experimental values. In a relative sense, however, the agreement between observed and calculated dipole strengths is satisfactory.

In strongly acidic media alkanes react as hydrogen donating agents towards the positive radical ions of anthracene, perylene and tetracene. The aromatic radical ions appear to be converted into their related proton complexes. These proton complexes reduce quinones to hydroquinones. Qualitative data on the latter reaction are discussed in relation to its mechanism. A direct reduction of quinones by alkanes has not been observed.

The effect of dye-doping in ambipolar light-emitting organic field-effect transistors (LE-OFETs) is investigated from the standpoint of the carrier mobilities and the electroluminescence (EL) characteristics under ambipolar operation. Dye-doping of organic crystals permits not only tuning of the emission color but also significantly increases the efficiency of ambipolar LE-OFETs. A rather high external EL quantum efficiency (∼0.64%) of one order of magnitude higher than that of a pure p-distyrylbenzene (P3V2) single crystal is obtained by tetracene doping. The doping of tetracene molecules into a host P3V2 crystal has almost no effect on the electron mobility and the dominant carrier recombination process in the tetracene-doped P3V2 crystal involves direct carrier recombination on the tetracene molecules.

An asymmetric twistacene, 1',4'-diphenyl-naphtho-(2'.3':1.2)-pyrene-6'-nitro-7'-methyl carboxylate (tetracene 2), was synthesized by using benzyne-trapping chemistry. Its structure, determined by X-ray crystallography, confirmed that this material has a twisted topology with torsion angles as high as 23.8(3) degrees. Organic light-emitting devices using tetracene 2 as either charge-transporting materials or emitters have been fabricated. The results indicate that this material has bipolar transporting behavior in these devices.

We synthesized 1,4-dipropyltetracene on a 200-mg scale, the key step of which involved a Diels-Alder reaction between alkyl-substituted o-quinodimethane, generated in situ, and 1,4-naphthoquinone. The product was obtained as an orange solid, which was soluble in organic solvents including hexane. The optical properties of the product in solution showed no marked differences from those of other 1,4,7,10-tetraalkyltetracenes. Solid-state absorption and fluorescence spectra exhibited 20-30 nm blueshifts compared with those of 1,4,7,10-tetrapropyltetracene. X-ray analysis revealed that two propyl groups were coplanar with the tetracene ring, that there was no π overlap along the stacking direction, and that the molecules formed a herringbone structure. The peripheral alkyl chains were found to be important for controlling the molecular packing and optical properties in the solid state.

We have synthesized 1,4,7,10-tetraisoalkyltetracenes from a 2,6-naphthodiyne precursor and 2,5-diisoalkylfurans as the starting materials (isoalkyl: isopropyl, isobutyl, and isopentyl). The tetracene molecules exhibited crystallochromy: The solid-state colors of the isopropyl, isobutyl, and isopentyl derivatives were yellow, red, and orange-yellow, respectively. In contrast, there were no marked differences in the optical properties of these compounds in solution. The isopropyl derivative exhibited the highest fluorescence quantum yield in the solid state of 0.90 in the series of alkylated tetracenes. X-ray analysis revealed that there were significant structural differences in alkyl conformation and crystal packing. The crystallochromy effects are derived from the unique crystal-packing patterns. The fluorescence quantum yields in the solid state probably depend on the relative positional relationship of the nearest neighboring molecules in one column as well as the crystal rigidity.

Organic single crystals have been well researched for many years. Typical vapor-phase growth of organic crystals developed from vertical to horizontal growth in order to achieve improved crystalline quality. Recently, a field-effect study on these single-crystal semiconductors demonstrated high carrier mobilities, up to ca. 15 cm Vs, along with anisotropic charge-transport properties. These single-crystal transistors were usually fabricated with rigid and thick crystals (tens of micrometers to millimeters), which were fragile and difficult to process because of poor mechanical properties. Recently, a growth method affording thin, 150 nm thick, organic crystals demonstrated the processability of single-crystal transistors on flexible substrates, and these organic crystals could be patterned on individual channels for transistors. However, in addition to transistor studies of these organic crystals, other types of electronic applications, such as two-terminal devices, have not yet been realized, mainly because of the difficultly processing thick crystals. In this Communication, we report organic single-crystal photovoltaics fabricated from single pieces of thin tetracene crystals on bilayer heterojunctions with fullerene (C60) thin films. These organic singlecrystal devices exhibited excellent diode behavior with rectifying ratios of 10 and an external power conversion efficiency (PCE) of ca. 0.34 %. By employing these high-quality single crystals in two-terminal devices, high-performance optoelectronic devices, such as organic diodes, photovoltaics, and photodetectors, become possible alternatives for large-area, low-cost flexible electronics. The quality of the single crystals was examined by cross-polarized microscopy, X-ray powder diffraction (XRD), and single-crystal X-ray diffraction. The optical microscopy images (Fig. 1a and b) recorded at 0° and 90° from the entrance polarizer and exit analyzer, respectively, show large birefringence, confirming the anisotropic crystalline nature of the tetracene crystals. The XRD data exhibit strong and narrow first (001) and second order (002) reflections (Fig. 1c), indicating the tetracene crystal is c-oriented, with molecular-plane growth along the vertical direction. The crystal data obtained for tetracene confirm a C18H6 molecular formula with a molecule weight of 222.23 g mol. The lattice constants are a = 6.02 ± 0.025 A, b = 7.77 ± 0.032 A, c = 12.46 ± 0.054 A, a =101.11 ± 0.078°, b = 99.41 ± 0.092°, and c = 94.40 ± 0.088°, and tetracene crystallizes with a triclinic crystal structure in space group P 1. The coordinates for tetracene can be obtained in the crystallographic information file (CIF) format from the Cambridge Crystallographic Data Center (CCDC), and the above crystallographic data are consistent with the data in the CCDC. Both the strong birefringence and the XRD results indicate these organic single crystals are of high quality. A schematic structure of a single-crystal solar cell is shown in Figure 2a. The device structure comprised a poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS)coated indium tin oxide (ITO) substrate, a tetracene crystal, evaporated thin films of C60 and bathocuproine (BCP), and an aluminum thin-film electrode. We note that thin crystals (ca. 200 nm) used in this study conformed better on substrates C O M M U N IC A IO N

2,3-Didecyloxytetracene (2,3-DDOT) is a yellow-orange soluble derivative that undergoes a strong de-coloration upon irradiation with visible light (470 nm). This is due to a photoreaction (Φr = 5.9 × 10−3) that leads to the formation of four photodimers, involving only the two central rings of the tetracene core. Copyright © 2007 John Wiley & Sons, Ltd.