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A survey of all crystal structures of rubrene materials in the Cambridge Structural Database is presented. Although the chemical substitution landscape is wide, hydrogen bonding functionalities are absent. Recognition motifs frequently found in crystals are the “slipped-cofacial” molecular pairing, and herringbone or purely translational 3-D propagation. Packing modes are classified in terms of structure determinants, cohesive energies of pairs of molecules in closer contact computed by the CLP atom-atom potential field. In these terms, crystal isomorphism with different chemical substitution is quantitatively assessed. Polymorphs are relatively few, perhaps due to poor solubilities that hamper crystallization screenings. True polymorphs are also identified by structure determinant patterns, and a new polymorph of the di-p-nitrophenyl derivative has been prepared and characterized by X-ray diffraction. Crystal morphologies of selected rubrenes have been predicted by Hartman's Periodic Bond Chain approach using PIXEL attachment energies; there is good agreement with experimental morphologies of crystals grown by sublimation. The good results obtained by CLP and PIXEL show promise for a computationally cheap access to lattice energies and morphology prediction. In general, from our overview it looks like sensitive spots in the driving forces for rubrene packing are the 4-substitution sites at the lateral rings, with substituents of moderate steric bulk. Peripheral substitution at the tetracene core seems to be less relevant. Our survey provides a structural background fostering new ideas on the synthesis and planning of physical properties of rubrenes.

The inclusion of functional molecules as substitutional dopants in single crystals of organic hosts with complementary optical properties provides a versatile strategy to tune optical and magnetic properties in view of their applications in opto-electronics and spintronics. Here, by combining electron spin resonance and optical spectroscopy, isolated triplet exciton states with distinct emission and absorptive resonance modes from two magnetically inequivalent sites of pentacene within the picene crystal are detected at room temperature. This is possible due to the incorporation of a low-doping, 1% mol/mol of pentacene into the monoclinic polymorph of picene high-quality single crystals. In addition, delayed fluorescence—optically detected magnetic resonance (ODMR) studies demonstrate efficient spin-dependent optical activities that are tuned by crystallographically oriented magnetic fields. These properties are particularly appealing for the exploitation of pentacene in room-temperature spin-driven opto-electronics, quantum sensing and in microwave amplification by stimulated emission of radiation (MASER). Graphical abstract: Triplet excitons of pentacene molecules doped into a picene single crystal provide microwave emission and absorptive resonance modes as well as large optically detected magnetic resonance contrast which can be tuned by magnetic field strength and direction. These properties make pentacene-doped picene single crystals promising materials for spin-driven opto-electronics and, in particular, in microwave amplification by stimulated emission of radiation (MASER). [Figure not available: see fulltext.].

This paper describes a laboratory course that introduces basic crystallographic data analysis to chemistry students encountering for the first time the world of crystals and crystal structures.The aim of the course is to provide students with direct contact with crystal structures and hands-on experience in structure analysis. To this end, a set of appropriately simple inorganic molecularstructures was selected, consisting of salts of hexaaqua metal ions with organic counter-ions. By exploiting the crystallographic tools available in the Cambridge Structural Database program Mercury, students learn how to visualize and analyse a set of atomic coordinates. In this way they learn how to extract bonding and structural information concerning intramolecular interactions in both salt components. Intermolecular interactions are next analysed by looking closely at supramolecular motifs and packing patterns generated by hydrogen bonds. This pragmatic approach turned out to be effective and extremely useful for summarizing many chemical concepts learned by students during a bachelor degree course in chemistry. The experience provides at the same time some basic capabilities for properly managing crystal structure analysis.

Despite recent advances, the synthesis of colloidal InSb quantum dots (QDs) remains underdeveloped, mostly due to the lack of suitable precursors. In this work, we use Lewis acid-base interactions between Sb(III) and In(III) species formed at room temperature in situ from commercially available compounds (viz., InCl3, Sb[NMe2]3 and a primary alkylamine) to obtain InSb adduct complexes. These complexes are successfully used as precursors for the synthesis of colloidal InSb QDs ranging from 2.8 to 18.2 nm in diameter by fast coreduction at sufficiently high temperatures (≥230 °C). Our findings allow us to propose a formation mechanism for the QDs synthesized in our work, which is based on a nonclassical nucleation event, followed by aggregative growth. This yields ensembles with multimodal size distributions, which can be fractionated in subensembles with relatively narrow polydispersity by postsynthetic size fractionation. InSb QDs with diameters below 7.0 nm have the zinc blende crystal structure, while ensembles of larger QDs (≥10 nm) consist of a mixture of wurtzite and zinc blende QDs. The QDs exhibit photoluminescence with small Stokes shifts and short radiative lifetimes, implying that the emission is due to band-edge recombination and that the direct nature of the bandgap of bulk InSb is preserved in InSb QDs. Finally, we constructed a sizing curve correlating the peak position of the lowest energy absorption transition with the QD diameters, which shows that the band gap of colloidal InSb QDs increases with size reduction following a 1/d dependence.