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Electronic disorder in organic semiconductor single crystals, manifested as parallel surface potential domains with potential variations ranging from tens to hundreds of mV, is observed by scanning Kelvin probe microscopy. Chemical etching and X-ray diffraction indicate that the potential domains are correlated with planar defects such as stacking faults. The results have important implications for understanding structure-transport relationships in organic semiconductor single crystals. [ABSTRACT FROM AUTHOR]

Isotopic substitution is a useful method to study the influence of nuclear motion on the kinetics of charge transport in semiconductors. However, in organic semiconductors, no observable isotope effect on field‐effect mobility has been reported. To understand the charge transport mechanism in rubrene, the benchmark organic semiconductor, crystals of fully isotopically substituted rubrene, 13C‐rubrene (13C42H28), are synthesized and characterized. Vapor‐grown 13C‐rubrene single crystals have the same crystal structure and quality as native rubrene crystals (i.e., rubrene with a natural abundance of carbon isotopes). The characteristic transport signatures of rubrene, including room temperature hole mobility over 10 cm2 V−1 s−1, intrinsic band‐like transport, and clear Hall behavior in the accumulation layer of air‐gap transistors, are also observed for 13C‐rubrene crystals. The field‐effect mobility distributions based on 74 rubrene and 13C‐rubrene devices, respectively, reveal that 13C isotopic substitution produces a 13% reduction in the hole mobility of rubrene. The origin of the negative isotope effect is linked to the redshift of vibrational frequencies after 13C‐substitution, as demonstrated by computer simulations based on the transient localization (dynamic disorder) scenario. Overall, the data and analysis provide an important benchmark for ongoing efforts to understand transport in ordered organic semiconductors. [ABSTRACT FROM AUTHOR]

Thesynthesis of dioxolane-functionalized hexacenes and heptacenesis reported. While heptacenes were too reactive to be successfullyisolated, hexacenes showed higher stability and characteristic long-wavelengthfluorescence both in solution and in the solid state as crystallinepowders. [ABSTRACT FROM AUTHOR]

Approaches to control the self‐assembly of aromatic structures to enhance intermolecular electronic coupling are the key to the development of new electronic and photonic materials. Acenes in particular have proven simple to functionalize to induce strong π‐stacking interactions, although finer control of intermolecular π‐overlap has proven more difficult to accomplish. In this report, we describe how very weak hydrogen bonding interactions can exert profound impact on solid‐state order in solubilized pentacenes, inducing self‐assembly in either head‐to‐tail motifs with strong 2‐D π‐stacking, or head‐to‐head orientations with much weaker, 1‐D π‐stacking arrangements. In order to achieve 3‐D π‐stacking useful for photovoltaic applications, we elaborated a series of diethynyl pentacenes to their trimeric dehydro[18]annulene forms. These large, strongly interacting structures did indeed behave as acceptors in polymer photovoltaic devices. [ABSTRACT FROM AUTHOR]

We report the simultaneous observation of geminate and nongeminate triplet-triplet annihilation in a solution-processable small molecule TIPS-tetracene undergoing singlet exciton fission. Using optically detected magnetic resonance, we identify recombination of triplet pairs directly following singlet fission, as well as recombination of triplet excitons undergoing bimolecular triplet-triplet annihilation. We show that the two processes give rise to distinct magnetic resonance spectra, and estimate the interaction between geminate triplet excitons to be 60 neV. [ABSTRACT FROM AUTHOR]