New heteroacenes, named coumarinacenes, have been designed, synthesized and characterized. They possess visible absorption and orange-red emission that are far beyond those of benzo[g]coumarins. They exhibit deep HOMO energy levels, and reveal excellent thermal, photochemical and air sta-Coumarins are pyranone-annulated benzenes (2H-benzopyran-2-ones) that are ubiquitous in nature. [1] They are actually popular for their wide spectrum of biological and pharmacological activities, [2a] such as, antioxidant, [2b] antidepressant, [2c] anticoagulant, [2d] anti-inflammatory, [2e] antifungal, [2f ] antitumor, [2g] anti-HIV, [2h] antibiotic, [2i] etc., and for their excellent biocompatibility. [1] Structurally simple derivatives of coumarin exhibit rich photophysical and photochemical properties (high photoluminescence quantum yields, large Stokes shifts and good photostability) paving their entry into modern photonic applications; laser dyes, [3a,3b] non-linear optics, [3c] two-photon bioimaging [3d] and sensing [3e] are some examples. Moreover, coumarin derivatives are recently being exploited as functional materials in organic light emitting devices, [4a,4b] liquid crystals, [4c] dye-sensitized solar cells, [4d,4e] electron and energy transfer systems, [4f,4g] and fluorescent probes. [4h] Despite the broad utility of coumarins, the low-lying absorption and emission wavelengths (due to shorter conjugation lengths) are primarily the bottlenecks in furthering their applications. In an effort to overcome the limitations, considerable attention is devoted in recent times for the development of novel π-expanded coumarin dyes. [5] Benzocoumarins-the simplest π-expanded benzene-fused coumarins-indeed absorb and emit light in the longer wavelength region when compared to parent coumarins (Scheme 1). [6] Among the other isomeric [a] A

The effect of substrate temperature and deposition rate on the film morphology, crystallinity, and electronic properties of Pentacene transistors treated with hexamethyldisilazane (HMDS) is studied. The gate bias dependence of mobility is used to estimate the width of the density of states and thereby quantify the disorder of the highest occupied molecular orbital. A low deposition rate and the substrate held at room temperature are shown to be the optimal conditions for good mobility (0.20 cm2 V−1 s−1) and low electronic disorder (50 ± 10 meV). X-ray diffraction measurements are performed to quantify the ratio of the two crystalline phases (thin-film phase and bulk phase) present in the film. The crystalline phases, rather than grain size, plays a significant role in determining the charge carrier mobility. Film deposition with the substrate at room temperature leads to low electronic disorder as the film is composed of one crystalline phase (thin-film phase), while high substrate temperature makes the film increasingly polymorphic, leading to increased electronic disorder (up to 230 meV). A high deposition rate leads to poor morphology of Pentacene near the source/drain electrode edge, thereby leading to increased contact resistance and electronic disorder. Hence, a low growth rate at room temperature is required for HMDS treated substrates to induce good crystalline properties of the film in the channel region, which results in enhanced electronic properties of the transistors.

The Cover Feature shows a representation of a 21st century molecular unition (the act of joining of hands) of the 19th century molecular couple (structures in blue) with a purpose of rediscovering a new life together (structure in red). More information can be found in the Communication by S. Dutta, P. Venkatakrishnan et al.

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