The impact of systematic structural variation on the energetics of π-π stacking interactions and associated computed charge transfer integrals of crystalline diketopyrrolopyrroles

No abstract

Surface-enhanced resonance Raman scattering (SERRS) of a model derivative of TNT was detected using a microflow cell designed within the framework of the lab-on-a-chip concept, using only the analyte and readily available reagents. The SERRS substrate, silver colloid, was prepared in situ, on-chip, by borohydride reduction of silver nitrate. The silver colloid was imaged within the chip using a white light microscope in either transmission or, due to the high reflectivity of the colloid, reflection mode. A fine stream of colloid approximately 30 microm in width was formed in a 250-microm-wide channel at the point where the colloid preparation reagents met. The chip was designed to produce a concentrated stream of colloid within a laminar regime, such that particles did not readily disperse into the fluid. One result of this was to reduce the effective volume of analysis. Attempts to deliberately disrupt this stream with microstructured pillars, fabricated in the fluidic channels, were unsuccessful. The chip was also designed to have the appropriate dimensions for detection using a modern Raman microscope system, which collects scattering from a very small volume. A dye derived from TNT was used as a model analyte. Quantitative behavior was obtained over 4 orders of magnitude with a detection limit of 10 fmol. This performance is between 1 and 2 orders of magnitude better than that achieved using a macroflow SERRS cell. The technique has the added advantage that both reagent consumption and effluent production are greatly reduced, leading to reduced operating costs and a decreased environmental impact

Sensitive optical detection of nitroaromatic vapours with diketopyrrolopyrrole thin films is reported for the first time and the impact of thin film crystal structure and morphology on fluorescence quenching behaviour demonstrated.

Intermolecular interactions and energetics in the crystalline π-π stacks and associated model dimer systems of asymmetric halogenated diketopyrrolopyrroles

Four novel systematically fluorinated DPPs and their single crystal structures are reported.Structures involving direct fluorination of the DPP core phenyl rings and N-benzyl groups, display 1-dimentional π-π stacking motifs; a characteristic of N-benzyl substitution, where long and short molecular axis displacement is induced by isosteric substitution of phenylic hydrogen atoms for fluorine atoms. This characteristic stacking behaviour is destroyed upon trifluoromethyl substitution at the para position of the core phenyl rings, in one case affording a novel molecular conformation and π-π dimer pair exhibiting a higher intermolecular interaction energy than any other structurally analogous DPP based system reported previously. This crystal structure also exhibits a unique orthogonal association of the π-π dimer pairs along the crystallographic a and b axes, resulting in the formation of a framework that is characterised by well-defined channels perpetuating along the length of the crystallographic c axis. The role of fluorine induced stabilisation and its impact on optoelectronic properties in these systems is identified via analysis of computed intermolecular interactions for all the crystal extracted nearest neighbour dimer pairs and their associated cropped equivalents. Our results clearly reinforce the positive role of benzyl substitution in DPP crystal structures to enhance optoelectronic behaviour. More importantly they demonstrate the significant impact small changes in molecular structure can have on the solid state properties of this molecular motif, particularly when fluorination is involved.ABSTRACT: Rationalising the effects of molecular substitution in π-conjugated organic materials arising from well-defined intermolecular interactions, which can influence the formation of predefined packing motifs and control the emergence of π-π stacking represents a current challenge in supramolecular design. Significant effort is potentially required to manage the impact on solid state packing behaviour in materials that have been molecularly tuned to carry out specific photophysical and electrochemical functions. In this regard, fluorine substitution in π-conjugated systems has seen a recent surge of interest, primarily aimed towards 3 the development of materials with enhanced optical and optoelectronic behaviour. In light of this interest, in the following study, we report the synthesis and single crystal structures from a series of four novel and structurally related, symmetric, fluorinated N-benzyl substituted diketopyrrolopyrroles (DPPs). Two of the investigated series exhibit slipped cofacial π-π dimer pairs, which are consistent with those reported by us previously in halogenated DPPs.Significantly, this characteristic stacking motif of N-benzyl substituted DPPs can be carefully modified via the replacement of hydrogen atoms with trifluoromethyl and isosteric fluorinehydrogen substituents. In the case of trifluoromethyl substitution, we identify a previously unobserved packing motif exhibiting a framework...

Selective chemical functionalisation of 2,4,6-trinitrotoluene to a surface enhanced resonance Raman active species for sensitive detection.

Two dimensional π–π model dimer system will enable researchers to predict charge transport properties for phenyl-based diketopyrrolopyrroles using their single crystal π-stacking data.