Photophysical and Chiroptical Properties of the Enantiomers of N,N'-Bis(1-phenylpropyl)-2,6-pyridinecarboxamide and their Chiral 9-Coordinate Ln3+ Complexes.

The R,R and S,S enantiomers of N,N'-bis(1-phenylpropyl)-2,6-pyridinedicarboxamide, L(Et), react with Ln3+ ions (Ln = La, Eu, Gd, and Tb) to give stable [Ln((R,R)- and (S,S)-L(Et))3]3+ in anhydrous acetonitrile solution, as evidenced by various spectroscopic measurements, including NMR and luminescence titrations. In addition to the characteristic Eu3+ and Tb3+ luminescence bands, the steady-state and time-resolved luminescence spectra of the aforementioned complexes show the residual ligand-centered emission of the 1ππ* to 3ππ* states, indicating an incomplete intersystem crossing (ISC) transfer from the 1ππ* to 3ππ* and ligand-to-Ln3+ energy transfer, respectively. The high circularly polarized luminescence (CPL) activity of [Eu(L(Et))3]3+ confirms that using a single enantiomer of L(Et) induces the preferential formation of one chiral [Eu(L(Et))3]3+ complex, consistent with the [EuL 3]3+ complexes formed with other ligands derived from a 2,6-pyridine dicarboxamide moiety. Furthermore, the CPL sign patterns of complexes with (R,R) or (S,S) enantiomer of L(Et) are consistent with the CPL sign pattern of related [LnL 3]3+ complexes with the (R,R) or (S,S) enantiomer of the respective ligands in this family.

Structural and photophysical properties of visible- and near-IR-emitting tris lanthanide(III) complexes formed with the enantiomers of N,N'-bis(1-phenylethyl)-2,6-pyridinedicarboxamide.

The enantiomers of N,N'-bis(1-phenylethyl)-2,6-pyridinedicarboxamide (L), namely, (R,R)-1, and (S,S)-1, react with Ln(III) ions to give stable [LnL(3)](3+) complexes in an anhydrous acetonitrile solution and in the solid state, as evidenced by electrospray ionization mass spectrometry, NMR, luminescence titrations, and their X-ray crystal structures, respectively. All [LnL(3)](3+) complexes [Ln(III) = Eu, Gd, Tb, and Yb; L = (R,R)-1 and (S,S)-1] are isostructural and crystallize in the cubic space group I23. Although the small quantum yields of the Ln(III)-centered luminescence clearly point to the poor efficiency of the luminescence sensitization by the ligand and the intersystem crossing and ligand-to-metal energy transfers, the ligand triplet-excited-state energy seems relatively well suited to sensitize many Ln(III) ion's emission for instance, in the visible (Eu and Tb), near-IR (Nd and Yb), or both regions (Pr, Sm, Dy, Er, and Tm).

Optical isomers of N,N'-bis(1-phenylethyl)-2,6-pyridinedicarboxamide coordinated to europium(III) ions as reliable circularly polarized luminescence calibration standards.

The synthesis of two optical isomers of N,N'-bis(1-phenylethyl)-2,6-pyridinedicarboxamide and the constant circularly polarized luminescence (CPL) activity of their acetonitrile trivalent europium complex solutions over a long period of time open new perspectives for performing accurate routine CPL calibration tests at low cost.

charge storage behavior of nanowire transistors functionalized with bis(terpyridine)-Fe(II) molecules: dependence on molecular structure.

We studied the influence of three bis(terpyridine)-Fe(II) molecules-(X-tpy)2FeCl2 (X = H (1), SAc (2), and 4-phenyl-SAc (3)-on charge storage of a nanowire transistor. The molecules were assembled on the surface of an indium oxide nanowire that forms the conduction channel of the transistor. We found that the charge storage characteristics of such a device strongly depends on the structure of the terpyridine ligand: both retention time (tau) and threshold voltage shift (DeltaVth) increased in the order of 1 < 2 < 3, with tau of 200 s, 12 h, and 287 h and DeltaVth at 4.8, 12, and 28 V, respectively. Furthermore, when we placed the devices with molecules 1 and 3 in a vacuum and recorded the I-Vg curves in a two-day period, we observed higher hysteresis stability for device with molecule 3. For example, DeltaVth was reduced from 4.8 to 1.7 V for the device with molecule 1, while there was no reduction in DeltaVth for the device with molecule 2. These results suggest that thiolate headgroup and/or longer ligand length raises the charge tunneling barrier and results in longer charge retention and wider, more stable memory window. This work demonstrates the potential of chemical synthesis toward tailored device characteristics.