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A series of alternating copolymers of a dithienylethene with di‐n‐alkyl‐fluorene (P1–P3), di‐n‐hexylphenylene (P4), 9‐heptadecanylcarbazole (P5), and 4,8‐bis(3,5‐dioctyl‐2‐thienyl)‐1,5‐dithia‐s‐indacene (P6) are designed, synthesized, and characterized. All of the polymers are soluble in common organic solvents such as chloroform, dichloromethane, toluene, and tetrahydrofuran. The side‐chain length affected the solubility of the polymer, molecular weight, and the glass transition temperature. Solutions of P1–P6 show photochromism with high quantum yields of 6‐π electrocyclization (41–87%) and cycloreversion (0.4–1.1%). These polymers also formed uniform thin films and the rates of solid state photoisomerization are measured relative to P4, which has the highest cyclization and cycloreversion rates. The color of the photochromic polymer is tuned according to the comonomer and the maximum absorption wavelength ranged from 569 to 675 nm in the closed isomeric form. All the polymers are thermally stable and show no signs of photodegradation after being exposed to UV‐light for 120 min in air. Based on these promising results, these polymers may be useful for multifunctional organic electronic devices. [ABSTRACT FROM AUTHOR]

Solution-processing of organic light-emitting diode films has potential advantages in terms of cost and scalability over vacuum-deposition for large area applications. However, solution processed small molecule films can have lower overall device performance. Here, novel molecular dynamics techniques are developed to enable faster simulation of solvent evaporation that occurs during solution processing and give films of thicknesses relevant to real devices. All-atom molecular dynamics simulations are then used in combination with kinetic Monte Carlo transport modeling to examine how differences in morphology stemming from solution or vacuum film deposition affect charge transport and exciton dynamics in films consisting of light-emitting bis(2-phenylpyridine)(acetylacetonate)iridium(III) [Ir(ppy)2(acac)] guest molecules in a 4,4′-bis(N-carbazolyl)biphenyl host. While the structures of the films deposited from vacuum and solution were found to differ, critically, only minor variations in the transport properties were predicted by the simulations even if trapped solvent was present. [ABSTRACT FROM AUTHOR]

Emissive layers in phosphorescent organic light-emitting diodes commonly make use of guest–host blends such as Ir(ppy)3:CBP to achieve high external quantum efficiencies. However, while the Ir(ppy)3:CBP blend has been studied experimentally, crucial questions remain regarding how exciton diffusion is dependent on the distribution of the guest in the host, which can currently only be addressed at the atomic level via computational modeling. In this work, kinetic Monte Carlo simulations are utilized to gain insight into exciton diffusion in Ir(ppy)3:CBP blend films. The effects of both guest concentration and exciton density on various system properties are analyzed, including the probability of singlet excitons being converted to triplets, and the probability of those triplets decaying radiatively. Significantly, these simulations suggest that triplet diffusion occurs almost exclusively via guest–guest Dexter transfer and that concentration quenching of triplets induced by guest–guest intermolecular dipole-dipole interactions has a negligible effect at high exciton densities due to the prevalence of triplet–triplet annihilation. Furthermore, results for vacuum deposited morphologies derived from molecular dynamics simulations are compared to the results obtained using a simple cubic lattice approximation with randomly distributed guest molecules. We show that while differences in host-based processes such as singlet diffusion are observed, overall, the results on the fate of the excitons are in good agreement for the two morphology types, particularly for guest-based processes at low guest concentrations where guest clustering is limited. [ABSTRACT FROM AUTHOR]

Ir(ppy)3:CBP blends have been widely studied as the emissive layer in organic light emitting diodes (OLEDs), yet crucial questions about charge transport within the layer remain unaddressed. Recent molecular dynamics simulations show that the Ir(ppy)3 molecules are not isolated from each other, but at concentrations of as low as 5 wt. % can be part of connected pathways. Such connectivity raises the question of how the iridium(iii) complexes contribute to long-range charge transport in the blend. We implement a kinetic Monte Carlo transport model to probe the guest concentration dependence of charge mobility and show that distinct minima appear at approximately 10 wt. % Ir(ppy)3 due to an increased number of trap states that can include interconnected complexes within the blend film. The depth of the minima is shown to be dependent on the electric field and to vary between electrons and holes due to their different trapping depths arising from the different ionization potentials and electron affinities of the guest and host molecules. Typical guest-host OLEDs use a guest concentration below 10 wt. % to avoid triplet-triplet annihilation, so these results suggest that optimal device performance is achieved when there is significant charge trapping on the iridium(iii) complex guest molecules and minimum interactions of the emissive chromophores that can lead to triplet-triplet annihilation. [ABSTRACT FROM AUTHOR]

Electrical characteristics of two polymer thin-film transistors (TFTs) fabricated by spin-coating of P3HDT and P3HT are investigated. Higher field-effect mobility, a lower off current, a lower inverse subthreshold slope and a larger on current ratio is demonstrated by experimental results from the TFTs based on P3HDT.

An organic photochromic compound is explored as a new portable colorimetric sensor for nitroaromatics. This photochromic compound switches from colourless to pink upon exposure to ultraviolet light. In the presence of nitroaromatic explosive derivatives the photoswitching behaviour of the dithienylethene is suppressed, while a potential false positive (toluene) has little effect. The degree of photoswitching inhibition was determined by comparing the integrated visible absorption with the concentration of the analyte to give the pseudo Stern–Volmer constant ( KPSV ). The KPSV s measured varied from 12900 ( p -nitrotoluene) to 236 M–1 (toluene), which were directly related to the analyte absorption at the excitation wavelength. [ABSTRACT FROM AUTHOR]