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Perylenediimides (PDIs) are among the best performing organic luminescent materials, both in terms of emission efficiency and chemical and photochemical stability because of their rigid, symmetric and planar structure; however, they exhibit very small Stokes shifts. The sizeable reabsorption of the emitted light limits the performances of perylenediimides in imaging applications and luminescent solar concentrators. Perylenemonoimides (PMIs) having an electron donating substituent in one of the free peri positions feature larger Stokes shift values while retaining high chemical stability. The selection of the most appropriate donor, both in terms of electron donating capability and steric demand, boosts emission efficiency and limits reabsorption losses. The synthesis, optical spectroscopy, molecular orbital computations, UPS, electrochemical, spectroelectrochemical, and multinuclear NMR investigation of a series of PMI derivatives functionalized with donors having different electronic characteristics and steric demands are discussed. Results are relevant for the fabrication of single layer plastic luminescent solar concentrators (LSC).

Pecan shell-based biochar is utilized as a filtration medium, sequestrant for metallic ions, soil conditioner, and other applications. One process for creating the biochar involves the use of phosphoric acid at high temperature in a partial oxygen atmosphere to produce a highly porous carbonaceous material. In this work, we found 129Xe NMR to be an excellent technique to study micropores in biochar. Thus, the 129Xe chemical shift in biochar was found to vary linearly with the xenon pressure; from the data an estimate of about 8–9 A could be proposed for the average pore diameter in pecan shell-based biochar. Through saturation recovery and 2-D NMR exchange experiments, information on the exchange between free versus bound xenon was obtained. Furthermore, correlations of 129Xe NMR data with the carbonization process conditions were made.

The interest in squaraine compounds, a relatively old class of cyanine-like dyes, has been recently renewed due to their potential usefulness in a large number of technologically relevant fields such as two photon absorbing materials, field effect transistors, solar cells, NIR emitting fluorescent probes and sensitizers for photo dynamic therapy. In the case of symmetric compounds, the squaraine electronic structure is reminiscent of that of symmetric cyanines. In the case of nonsymmetric squaraines the HOMO-LUMO transition is characterized by a charge transfer component responsible for a sometimes sizeable band broadening, also reflected in a relevant second order nonlinear optical behaviour. The aim of the present paper is the design, synthesis and multidisciplinary characterization of a series of nonsymmetrical heterocycle-based squaraines, a study directed towards a general understanding of the deviation from the cyanine limit in this class of dyes. We exploit the electric field induced second harmonic generation technique as a tool for the charge transfer character evaluation and, together with other hints coming from UV-Vis, NMR and cyclic voltammetry, we show how the directionality of the HOMO-LUMO excitation can be characterized and accounted for in terms of the most relevant contribution of canonical structures for the squaraine ground state description. DFT/TDDFT calculations provide further insight to the electronic structure of representative compounds. © 2009 The Royal Society of Chemistry.