Search

Abstract Control of electrical doping is indispensable in any semiconductor device, and both efficient hole and electron doping are required for many devices. In organic semiconductors, however, electron doping has been essentially more problematic compared to hole doping because in general organic semiconductors have low electron affinities and require dopants with low ionization potentials that are often air-sensitive. Here, we adapt an efficient molecular doping method, so-called ion-exchange doping, to dope electrons in a polymeric semiconductor. We initially reduce the polymeric semiconductor using one electron transfer from molecular dopants, and then the ionized dopants in the resulting air-unstable films are replaced with secondary ions via cation exchange. Improved ambient stability and crystallinity of the doped polymeric semiconductors are achieved when a specific bulky molecular cation was chosen as the secondary ion, compared to conventional methods. The presented strategy can overcome the trade-off relationship between reducing capability and ambient stability in molecular dopants, and a wider selection of dopant ions will help to realize ambient-stable electron conductors.

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.

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).

This paper compares across six nations the mental health systems available to prisoners with the highest acuity of psychosis and risk combined with the lowest level of insight into the need for treatment. Variations were observed within and between nations. Findings highlight the likely impact of factors such as mental health legislation and the prison mental health workforce on a nation's ability to deliver timely and effective treatment close to home for prisoners who lack capacity to consent to treatment for their severe mental illness. The potential benefits of addressing the resulting inequalities are noted.

Background Family involvement has been identified as a key aspect of clinical practice that may help to prevent suicide. Aims To investigate how families can be effectively involved in supporting a patient accessing crisis mental health services. Method A multi-site ethnographic investigation was undertaken with two crisis resolution home treatment teams in England. Data included 27 observations of clinical practice and interviews with 6 patients, 4 family members, and 13 healthcare professionals. Data were analysed using framework analysis. Results Three overarching themes described how families and carers are involved in mental healthcare. Families played a key role in keeping patients safe by reducing access to means of self-harm. They also provided useful contextual information to healthcare professionals delivering the service. However, delivering a home-based service can be challenging in the absence of a supportive family environment or because of practical problems such as the lack of suitable private spaces within the home. At an organisational level, service design and delivery can be adjusted to promote family involvement. Conclusions Findings from this study indicate that better communication and dissemination of safety and care plans, shared learning, signposting to carer groups and support for carers may facilitate better family involvement. Organisationally, offering flexible appointment times and alternative spaces for appointments may help improve services for patients.

Despite advances in the design of thermally activated delayed fluorescence (TADF) emitters for devices, the effect of spin interactions is not well understood. Here, the authors report the role of spin-vibronic coupling in TADF organic emitters using transient electron spin resonance spectroscopy.

This review summarizes experiences at operational centers to forecast tropical cyclone (TC) intensity change as presented to the International Workshop on Tropical Cyclones (IWTC-9) in Hawaii in 2018. Some operational forecast centers have been able to leverage advances in intensity guidance to increase forecast skill, albeit incrementally, while others have struggled to make any significant improvements. Rapid intensity changes continue to present major challenges to operational centers and individual difficult cases illustrate the forecasting challenges. It is noteworthy that the realization of a recommendation from IWTC-8 in 2014, to adapt guidance initially developed for the North Atlantic and North-East Pacific to other basins, has led to improved forecast skill of some agencies. Recent worldwide difficult cases are presented so that the research community can further investigate, potentially leading to improved intensity forecasts when similar cases are observed in the future. Keywords: tropical cyclone, intensity, change, rapid intensification

This review summarizes techniques used by operational centers to forecast tropical cyclone intensity change as presented to the International Workshop on Tropical Cyclones (IWTC-9) in Hawaii in 2018. Recent advances and major changes over the past four years are presented, with a special focus on forecasting rapid intensity changes. Although intensity change remains one of the most difficult aspects of tropical cyclone forecasting, objective guidance has shown some improvement. The greatest improvements are realized when consensus methods are utilized, especially those that blend statistical-dynamical based guidance with dynamical ocean-coupled regional models. These models become even more skillful when initialized with inner core observational data. Continued improvement and availability of intensity guidance along with associated forecaster training are expected to deliver forecasting improvements in the future. Keywords: tropical cyclone, intensity, change, rapid intensification

Abstract A method to determine the doping induced charge carrier profiles in lightly and moderately doped organic semiconductor thin films is presented. The theory of the method of Charge Extraction by a Linearly Increasing Voltage technique in the doping-induced capacitive regime (doping-CELIV) is extended to the case with non-uniform doping profiles and the analytical description is verified with drift-diffusion simulations. The method is demonstrated experimentally on evaporated organic small-molecule thin films with a controlled doping profile, and solution-processed thin films where the non-uniform doping profile is unintentional, probably induced during the deposition process, and a priori unknown. Furthermore, the method offers a possibility of directly probing charge-density distributions at interfaces between highly doped and lightly doped or undoped layers.

Soluble alternating copolymers of N-(3,4,5-tri-n-dodecyloxyphenyl)dithieno[3,2-b:2′,3′-d]pyrrole donor groups and 2,3-di-n-decylquinoxaline, 2,3-di-n-decylpyrido[3,4-b]pyrazine, 2,3,6,7-tetrakis(n-decyloxy)benzo[a,c]phenazine, or 2,3,6,7-tetrakis(n-decyloxy)dibenzo[f,h]pyrido[4,3-b]quinoxaline acceptors were synthesised using Stille coupling reactions. Experimental absorption maxima in THF range from 645 to 770 nm. These optical data, along with the results of quantum-chemical calculations and electrochemical measurements, show that, as expected, the pyridopyrazine moiety acts as a stronger acceptor than quinoxaline and that the extended species benzophenazine and dibenzopyridoquinoxaline are stronger acceptors than quinoxaline and pyridopyrazine, respectively. Modest average hole mobilities of up to ca.3.0 × 10−4cm2V−1s−1were obtained in field-effect transistors. Bulk heterojunction photovoltaic devices made from blends of the benzo[a,c]phenazine-based polymer with 3′-phenyl-3′H-cyclopropa[1,9](C60-Ih)[5,6]fullerene-3′-butanoic acid methyl ester (1 : 3 weight ratio) exhibited average power conversion efficiencies up to 1.4%. [ABSTRACT FROM AUTHOR]

The electronic and optical properties of 2,6-dialkyl and 2,6-bis(5-alkyl-2-thienyl) derivatives of the fused-ring systems 4H-cyclopenta[2,1-b:3,4-b′]bithiophene, 4,4-di-n-hexyl-4H-cyclopenta[2,1-b:3,4-b′]bithiophene, 4H-cyclopenta[2,1-b:3,4-b′]bithiophene-4-one, 4-alkyl and 4-aryldithieno[3,2-b:2′,3′-d]pyrrole, 4-phenyldithieno[3,2-b:2′,3′-d]phosphole, 4-phenyldithieno[3,2-b:2′,3′-d]phosphole 4-oxide, dithieno[3,2-b:2′,3′-d]thiophene, dithieno[3,2-b:2′,3′-d]thiophene 4-oxide, and dithieno[3,2-b:2′,3′-d]thiophene 4,4-dioxide have been compared to those of the analogous unbridged 5,5′-substituted 2,2′-bithiophene derivatives using electrochemistry, UV−visible absorption and emission spectroscopy, and DFT and TD-DFT calculations. The planarization in the fused-ring compounds means that the methylene-bridged cyclopentabithiophenes are more readily oxidized than their unbridged bithiophene analogues. In each case, the bridging group (X) lies on a nodal plane of the HOMO; accordingly, within each series of fused-ring compounds, electrochemical oxidation potentials and calculated ionization potentials depend primarily on the inductive donor/acceptor strength of the bridging group. On the other hand, significant LUMO coefficients can be found on X groups with π-donor or acceptor properties; accordingly, the electrochemical reduction potentials, calculated electron affinities, and the energies of the HOMO→LUMO optical transitions depend on both inductive and mesomeric donor and acceptor strengths. In particular, within the 2,6-bis(5-alkyl-2-thienyl) series, increasingly electron-withdrawing bridging groups lead to a bathochromic shift and weakening of the low-energy absorption band relative to that of methylene- or π-donor-bridged examples and also to a loss of vibronic structure, with the compound that has the strongest π-accepting bridge of those examined (X = CO) showing a particularly low-energy and weak band. The fluorescence of acceptor-bridged compounds exhibits greater Stokes shifts and a loss of vibronic structure relative to those of methylene- or π-donor-bridged analogues, with the carbonyl-bridged derivative showing no observable fluoresence. These results can be related to increasing localization of the LUMO on the core and toward the bridging group, leading to increased charge-transfer character for the first excited state. The radical cations of some examples have been generated by chemical oxidation and investigated using visible-NIR and ESR spectroscopy and DFT and TD-DFT calculations. The absorption spectra of the radical cations of the 2,6-bis(5-alkyl-2-thienyl) compounds are generally similar to those previously reported for quaterthiophene derivatives, while the hyperfine couplings obtained from ESR spectra are consistent with delocalization of the unpaired electron over both the core and terminal thienyl rings of the π system. [ABSTRACT FROM AUTHOR]

A series of highly soluble donor–acceptor (D–A) copolymers containing N-(3,4,5-tri-n-decyloxyphenyl)-dithieno[3,2-b:2′,3′-d]pyrrole (DTP) or N-(2-decyltetradecyl)-dithieno[3,2-b:2′,3′-d]pyrrole (DTP′) as donor and three different acceptors, 4,7-dithien-2-yl-[2,1,3]-benzothiadiazole, 4,9-dithien-2-yl-6,7-di-n-hexyl-[1,2,5]thiadiazolo[3,4-g]quinoxaline and 4,8-dithien-2-yl-2λ4δ2-benzo[1,2-c;4,5-c′]bis[1,2,5]thiadiazole (BThX, X = BTD, TQHx2, BBT, respectively) were synthesized by Stille coupling polymerizations. The optical and electrochemical properties of these copolymers were investigated, along with their use in field-effect transistors and photovoltaic devices. The band gaps (eV) estimated from UV-vis-NIR spectra and electrochemical measurements of the copolymers varied from ca.1.5–0.5 eV, and were consistent with quantum-chemical estimates extrapolated using density functional theory. Oxidative and reductive spectroelectrochemistry of the copolymers indicated they can be both p-doped and n-doped, and three to four differently colored redox states of the polymers can be accessed through electrochemical oxidation or reduction. The DTP-BThBTD and DTP-BThTQHx2copolymers exhibited average field-effect hole mobilities of 1.2 × 10−4and 2.2 × 10−3cm2/(Vs), respectively. DTP-BThBBT exhibited ambipolar field-effect characteristics and showed hole and electron mobilities of 1.2 × 10−3and 5.8 × 10−4cm2/(Vs), respectively. Bulk heterojunction photovoltaic devices made from blends of the copolymers with 3′-phenyl-3′H-cyclopropa[1,9](C60-Ih)[5,6]fullerene-3′-butanoic acid methyl ester (PCBM) (1:3 weight ratio) exhibited average power conversion efficiencies as high as 1.3% under simulated irradiance of 75 mW/cm2. [ABSTRACT FROM AUTHOR]

Siloles are attractive building blocks for the design and synthesis of organic semiconductors that exhibit potential applications in light-emitting diodes, solar cells, field-effect transistors, and sensors. Understanding how molecular engineering of the electronic structures can help control the properties of these materials has attracted significant research effort. In the present review we illustrate the current state-of-the-art of the molecular engineering of siloles, especially focusing on the effects of substituents and on the electronic structure of siloles. [ABSTRACT FROM AUTHOR]

A series of silole molecules with fluorenyl substituents at varying positions—1-(9,9-dimethylfluoren-2-yl)-1,2,3,4,5-pentaphenylsilole, 1-(fluoren-9-yl)-1,2,3,4,5-pentaphenylsilole, 1,1,3,4-tetraphenyl-2,5-bis(9,9-dimethylfluoren-2-yl)silole, and 1,1-diphenyl-2,3,4,5-tetrakis(9,9-dimethylfluoren-2-yl)silole—has been synthesized and compared to the previously reported compounds, 1,1,2,3,4,5-hexaphenylsilole and 1,1-bis(9,9-dimethylfluoren-2-yl)-2,3,4,5-tetraphenylsilole. The effect of fluorenyl substitution pattern on the geometric, thermal, electronic, optical, and electroluminescence properties was investigated both experimentally and theoretically. Analysis of the X-ray crystal packing diagrams for two new fluorenyl-substituted siloles indicates the presence of π–π stacking and CH⋯π interactions in the solid state. Across the series, excellent thermal and morphological stabilities are displayed. Photoelectron/inverse-photoelectron spectroscopy measurements and density functional theory (DFT) calculations suggest that increased conjugation length through substitution at the 2- and 5-positions plays a more significant role in tuning the ionization potentials and electron affinities of these siloles than do inductive effects through substitution of the silicon. The electronic structure (e.g., HOMO–LUMO gap) and, hence, the optical absorption and fluorescence properties are also sensitive to the positions at which the fluorenyl groups are introduced, with substitution at the 2,5-positions having the largest effect. Solution-processed electroluminescent devices fabricated with the fluorenyl-substituted siloles as the emissive layer have luminous efficiencies as high as 3.6 cd A−1. [ABSTRACT FROM AUTHOR]

We report growth as well as structural, optical, and charge-transport properties of highly ordered thin films of a fused thiophene derivative, 6,6′-di-n-hexyl-[2,2′]bi(dithieno[3,2-b:2′,3′-d]thiophenyl) (DH-BDT). DH-BDT was synthesised with the aim of fabricating high quality, molecularly aligned thin films for organic electronic applications. Structural phase transitions are observed upon heating from room temperature, indicating the existence of three different polymorphs, denoted α, β and γ. The transition temperatures are Tα→β = 92 ± 2 °C and Tβ→γ = 140 ± 2 °C. The growth of thin films of DH-BDT can be controlled to afford either the β- or the γ-phase. Thermal annealing leads to the formation of large single crystalline grains with areas as large as 7 × 104μm2. The molecules in the γ-phase are cofacially aligned and show horizontally layered thin film growth. The good crystallinity and the large grain size in the γ-phase lead to hole mobilities up to μγ = 0.09 cm2 V−1 s−1, based on the measurement of space-charge-limited currents (SCLC). The β-phase consists of mutually shifted molecules, resulting in a lower hole mobility of 4.4 × 10−5 cm2 V−1 s−1 but improving the relative luminescence quantum yield by 140% relative to that of the γ-phase. Field-effect transistors of DH-BDT in the γ-phase have been fabricated and yield hole mobilities which are of the same order of magnitude as the SCLC mobilities. [ABSTRACT FROM AUTHOR]

The 2-dicyanomethylidene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) group has been identified as a particularly strong acceptor suitable for the realization of highly efficient second-order NLO chromophores. To provide guidelines for a further improvement of heterocyclic acceptors, we present Sum-Over-States (SOS) calculations of second-order polarizabilities (β) for a series of donor–π-bridge–acceptor (D–π–A) chromophores. In particular, we investigate the effect of replacing the oxygen atom of the furan ring in TCF by a variety of other groups, X (SiH2, CH2, C=CH2, NH, C=O, S, C=CHNO2, SO, and SO2). Overall β is found to increase with the inductive electron-withdrawing character of X, with β being further increased or decreased when X has π-accepting or π-donating character. Within the framework of the two-level model, the effects associated with the π-donating and accepting character can be understood in terms of destabilizing and stabilizing effects on the lowest unoccupied molecular orbitals of the dipolar chromophores. When using the stronger 3-methyl-4-cyano-5-dicyanomethylidene-2-oxo-3-pyrroline (TCP) acceptor and replacing the pyrroline nitrogen atom with the same range of X groups, the inductive electron-withdrawing and π-accepting or π-donating characters of X have the same impact on β as in the TCF motif. [ABSTRACT FROM AUTHOR]

The charge-carrier mobilities for three Ni bis(dithiolene) complexes have been determined using the steady-state space-charge limited current technique. A high mobility of 2.8 cm2 V−1 s−1 was observed for one compound, which exhibits a π-stacked columnar structure, in an annealed unsymmetrical melt-processed device. Energy-level considerations and field-effect transistor measurements suggest that this value represents an electron mobility. However, saturation mobilities measured for this compound in spin-coated field-effect transistors were found to be over two orders of magnitude lower than the space-charge limited current values. X-Ray diffraction shows a difference in morphology between thick melt-processed and thin spin-coated films and, therefore, a significant change in intermolecular packing between the device types may explain the discrepancy in mobilities obtained using the two techniques. [ABSTRACT FROM AUTHOR]

We report on photoinduced charge separation in solid films of two perylene diimides; intramolecular charge separation and recombination is correlated with a reduction in the yield of long-lived, intermolecular charge-separated species. [ABSTRACT FROM AUTHOR]

A narrow band-gap alternating copolymer of perylene diimide and bis(dithienothiophene) (2) and a polythiophene derivative substituted by a tris(thienylenevinylene) conjugated side chain (4) are used as acceptor and donor, respectively, in all-polymer solar cells (SCs). The optimized device based on the blend of 4 and 2 in the ratio 3:1 (w/w) gives a short circuit current (Jsc) of 5.02 mA cm-2 and a power conversion efficiency of 1.48%, under simulated AM 1.5 illumination at 100 mW cm-2. These values are among the highest values reported for all-polymer SCs. [ABSTRACT FROM AUTHOR]

The crystal structure of a cyanine dye rotaxane shows that the cyclodextrin is tightly threaded round the polymethine bridge of the dye; encapsulation dramatically increases the kinetic chemical stability of the radicals formed on oxidation and reduction of the dye, making it possible to observe the rotaxane radical dication by ESR and UV-vis-NIR spectroscopy. [ABSTRACT FROM AUTHOR]

Chromophores in which vinylene units and either pyrrole or dialkoxythiophene groups form the bridge between two diarylaminophenyl groups exhibit two-photon cross-sections of 1000–5000 GM at 600–650 nm. [ABSTRACT FROM AUTHOR]