We designed a stereodynamic system, where the chirality of the analyte serves as a template for the helicity of the first coordination sphere of Co(ii). Giant VCD bands induced by Co(ii) allow the measurement of a completely significant and conclusive VCD spectrum in only a few seconds and/or on minute quantities of the analyte. This paves the way for the development of similar protocols, overcoming the limitations due to weak VCD signals for the assignment of absolute configurations.

The use of stereodynamic probes is becoming one of the leading strategies for the fast and effective determination of enantiomeric excess. Recently, we reported a series of novel molecular architectures based on a modified tris(2-pyridylmethyl)amine complex (TPMA), which are able to amplify the electronic CD, in the case of Zn(II) assemblies and vibrational CD, in the case of Co(II) assemblies. Herein, we report a structural modification of the ligand with the purpose to obtain a fluorescent chiral probe. The study deals with the synthesis of the novel ligand, the formation of the self-assembly system with amino acids, and the study of the electronic CD and circularly polarized luminescence. KEYWORDS CD, CPL, enantiomeric excess, self-assembly, supramolecular chemistry | INTRODUCTIONIn the last few decades, several research groups have been studying chiral sensors because of the important applications that chiral molecules have in several fields of science, ranging from catalysis to materials. Under this respect, special attention has been paid to searching new methods and techniques for the determination of enantiomeric excess (ee) that are faster and cheaper than traditional chromatographic methods. [1][2][3][4] In this context, several supramolecular architectures have been developed to gather an optical signal that can be easily measured through the most common spectroscopic techniques, ie, circular dichroism (CD). [5][6][7][8][9][10][11][12][13][14][15] Usually, these supramolecular sensors possess at least one labile stereogenic element that interconverts between 2 enantiomeric forms. The addition of a chiral analyte leads preferentially to the formation of one diasteroisomer that furnishes back the optical chiral information. Within these stereodynamic probes, tris(2-pyridylmethyl)amine (TPMA)-based metal complexes have shown to be versatile chemical systems for the determination of ee. [16][17][18][19][20][21][22] This ligand assumes a propeller-like arrangement around the metal center that in solution is in equilibrium between the two helical configurations (clockwise and counterclockwise configuration is preferred, and the resulting diasteroisomer is able to provide a chiroptical signal. 23,24 Recently, we have started to combine the TPMA scaffold with dynamic covalent chemistry (DCC) of imines formation. [25][26][27][28][29]31 has already shown its fundamental role in the formation of new complex nano-architectures. In particular, we described two novel supramolecular architectures based on modified TPMA metal complexes (Scheme 1): the dinuclear 1-Zn-aa and 3-Zn-aa, and the trinuclears 2-Zn-aa and 2-Co-aa. These systems have shown to perform as probes for amino acids, 32-35 furnishing dichroic signals characteristic of the amino acidic side chain and proportional to the enantiomeric excess. While all systems are effective using electronic CD, the presence of cobalt(II) in 2-Co-aa induces additionally gigantic (or: huge) vibrational CD bands, allowing the measurement of a VCD spectrum in onl...

Novel cobalt, nickel, and iron complexes based on the pentadentate 8-hydroxyquinoline-di(2-picolyl)amine ligand were synthesized and thoroughly characterized. X-ray structures of both the cobalt and iron complexes were also obtained, showing the tendency to adopt a pseudo-octahedral geometry by coordination of an additional sixth ligand. These metal complexes were then studied as potential hydrogen-evolving catalysts (HECs) under both electrochemical and light-driven conditions. In particular, two different photochemical systems were tested involving either Ru(bpy)/ascorbic acid or Ir(ppy)(bpy)/TEA sensitizer/sacrificial donor couples. The electrochemical results showed that these metal complexes may behave as competent HECs. However, under photochemical conditions, only the cobalt compound displayed substantial hydrogen-evolving activity in both ruthenium- and iridium-based systems. The nickel and iron complexes, on the other hand, exhibited appreciable photocatalytic activity only in the iridium-based photochemical system, while showing negligible hydrogen evolution ability when employed in the ruthenium-based one.

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