We carried out a study of absorption (CD) and emission (CPL) chiroptical properties in the NIR region of two sets of Yb, Tm and Er complexes. The two complexes include...

Thiourea derivatives of 2-[(1 R )-1-aminoethyl]phenol, (1 S ,2 R )-1-amino-2,3-dihydro-1 H -inden-2-ol, (1 R ,2 R )-(1 S ,2 R )-1-amino-2,3-dihydro-1 H -inden-2-ol, and ( R )-1-phenylethanamine have been compared as chiral solvating agents (CSAs) for the enantiodiscrimination of derivatized amino acids using nuclear magnetic resonance (NMR) spectroscopy. Thiourea derivative, prepared by reacting 2-[(1 R )-1-aminoethyl]phenol with benzoyl isothiocyanate, constitutes an effective CSA for the enantiodiscrimination of N- 3,5-dinitrobenzoyl (DNB) derivatives of amino acids with free or derivatized carboxyl functions. A base additive 1,4-diazabicyclo[2.2.2]octane(DABCO)/ N , N -dimethylpyridin-4-amine (DMAP)/NBu 4 OH) is required both to solubilize amino acid derivatives with free carboxyl groups in CDCl 3 and to mediate their interaction with the chiral auxiliary to attain efficient differentiation of the NMR signals of enantiomeric substrates. For ternary systems CSA/substrate/DABCO, the chiral discrimination mechanism has been ascertained through the NMR determination of complexation stoichiometry, association constants, and stereochemical features of the diastereomeric solvates.

The reaction of benzoyl isothiocyanate with (1 R ,2 R )-1,2-bis(2-hydroxyphenyl)ethylenediamine afforded a new thiourea chiral solvating agent (CSA) with a very high ability to differentiate 1 H and 13 C NMR signals of simple amino acid derivatives, even at low concentrations. The enantiodiscrimination efficiency was higher with respect to that of the parent monomer, a thiourea derivative of 2-((1 R )-1-aminoethyl)phenol, thus putting into light the relevance of the cooperativity between the two molecular portions of the dimer in a cleft conformation stabilized by interchain hydrogen bond interactions. An achiral base additive (DABCO or DMAP) played an active role in the chiral discrimination processes, mediating the interaction between the CSA and the enantiomeric mixtures. The chiral discrimination mechanism was investigated by NMR spectroscopy through the determination of complexation stoichiometries, association constants, and the stereochemistry of the diastereomeric solvates.

A straightforward way for the preparation of mechanochromic polymers consists of incorporating a suitable content of a mechanophore in the polymeric matrix either by physical dispersion or via covalent functionalization. Although covalent incorporation may require demanding chemical efforts, this approach can offer significant advantages over physical dispersion. In this work, a common thermoplastic elastomer, styrene-b-(ethylene-co-butylene)-b-styrene triblock copolymer grafted with maleic anhydride (SEBS-MAH), was covalently functionalized with 1-aminomethylpyrene (AMP). MAH functional groups are covalently linked to the ethylene-co-butylene blocks, thus allowing a precise and selective confinement of the chromogenic AMP units in the soft block. Flat, fully conjugated pyrene units undergo the reversible formation of π−π aggregates, readily distinguishable by their red-shifted emission. These aggregates were heavily affected by the application of mechanical stimuli. Despite the low degree of mechanophore functionalization (about 1 wt %), uniaxial deformation of the polymer was reliably monitored via fluorescence and a clear drop in the excimer to monomer emission ratio (I E /I M ) was observed starting from 50% of strain. The marked mechanochromism was confirmed by emission lifetime measurements and also by near-field investigations. In addition, the mechanoresponse showed good reversibility after repeated stress−relaxation cycles. Control experiments performed on formulations comprising a physical dispersion of pyrene in unfunctionalized SEBS showed faint excimer emission and a negligible mechanochromic response up to 5 wt % of doping, in substantial agreement with the scanning near-field optical microscopy analysis. An evident drop of the I E /I M ratio occurred for 10 wt % of pyrene, albeit the excimer emission remained predominant even at the highest deformation, being a smaller fraction of pyrene moieties involved. Overall, the covalent approach appeared as an elegant procedure to confine the chromogenic unit in the soft phase of block copolymers and thus to provide an elastomeric film showing a detectable and reversible mechanochromic response with a modest (i.e., ∼1 wt %) amount of pyrene molecules, i.e., 10 times smaller compared to the dispersed system.

This study examines the use of an aggregation-induced enhanced emission fluorophore (TPE-MRh) to prepare red-emitting luminescent solar concentrators (LSCs) based on poly(methyl methacrylate) (PMMA) and poly(cyclohexyl methacrylate) (PCMA). TPE-MRh is a tetraphenylethylene (TPE) derivative bearing two dimethylamino push groups and a 3-methyl-rhodanine pull moiety, with absorption maxima at around 500 nm and fluorescence peak at 700 nm that strongly increases in solid-state. TPE-MRh displays a typical crystallizationinduced enhanced emission that has been rationalized by modeling the compound behavior in solution and solid-state via density functional theory calculations with the inclusion of the environment. TPE-MRh dispersed into 5 × 5 cm 2 polymer films with a thickness of 25 ± 5 μm has revealed a partial fluorescence quenching with fluorophore content. Quantum yields (QYs) below 10% for the 2 wt.% of doping have been addressed to the formation of less emissive micro-sized clusters of fluorophores. PMMA slabs with the same surface size but 3 mm of thickness and 200 ppm of TPE-MRh have provided QY of 36.5% thanks to the attenuation of the detrimental effects of fluorophore aggregation. This feature is reflected in the LSCs performance, with devices achieving the largest power collected by the photovoltaic cell.