A number of strategies exist to design molecular materials based on self-assembled peptides and their derivatives. [1] These include soft materials based on a variety of structural motifs including coiled-coils, [2,3] b-sheets, [4,5] b-hairpins, [6] and peptide amphiphiles. [7][8][9] In these systems, the peptide chains usually contain at least ten amino acids. It has been known for some time that using aromatic components in conjunction with peptides allows the use of much smaller peptides by taking advantage of p-stacking interactions. [10][11][12][13][14][15] One system that has been illustrated is that of N-fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF) which forms a hydrogel under physiological conditions. This example and other closely related aromatic short peptide derivatives are known to form fibrous hydrogels that have found applications in biological sensing [16] and cell culture. [13,17] Understanding of the supramolecular structures formed by these molecules will aid the rational design of new architectures tailored to the needs of specific biological and non-biological applications. However, to date a complete structure has not been proposed for any member of this class of self-assembly systems. Here we apply a number of spectroscopic techniques to Fmoc-FF and construct a model based on the data obtained comprising a new nanocylindrical molecular architecture based on p-p interlocked b-sheets. Transmission electron microscopy (TEM) and wide angle X-ray scattering (WAXS) was used to confirm the proposed model. Hydrogels of Fmoc-FF were prepared as described previously utilizing a sequential change in pH.[13] As shown in Figure 1a self-supporting gels were formed. The viscoelastic properties of the gels were assessed using oscillatory rheology. Figure 1b shows the mechanical spectrum obtained at room temperature for a Fmoc-FF (20 mmol L -1 ) gel. The storage modulus (G') is found to be approximately an order of magnitude larger than the loss modulus (G''), indicative of an elastic rather than viscous material. Both G' and G'' were found to be essentially independent of frequency over four decades (Fig. 1b). Such rheological behavior is characteristic of solid like gel materials. Light microscopy ( Fig. 1c) revealed a network of fine fibers with microscopic widths. Cryo Scanning Electron Microscopy (cryoSEM) revealed a dense network of flat ribbons with dimensions in the order of tens of nanometers (Fig. 1d). Circular dichroism (CD) was used to investigate the backbone orientation of the dipeptide within the hydrogel. CD analysis of peptide-based supramolecular materials is prone to artifacts. Usually only a narrow concentration range, where the hydrogel forms, can be used reliably to present a detectable CD signal, while showing no or little light scattering ef-

We report on the synthesis and photophysical properties of blue emitting iridium(iii) complexes. The use of a negatively charged ligand, such as a triazolyl pyridine, allows a facile preparation, maintaining the high energy emission (blue region) of heteroleptic complexes. We discuss the role played by electron withdrawing substituents of a different nature and also how the substitution position of the same group influences the spectroscopical behaviour.

Neutral heteroleptic mononuclear iridium(III) complexes with (2,4-difluoro)phenylpyridine and different pyridine-1,2,4-triazole ligands were synthesized and fully characterized. We investigated the effects of substituents in the 5-position of the triazole ring on the photophysical and electrochemical behavior. Increasing the electron-withdrawing capabilities generally leads to a lowering of the HOMO level with a consequent slight widening of the HOMO-LUMO gap and a blue shift in emission. The complexes reported exhibit high emission quantum yields and long luminescent lifetimes, typical of iridium(III) complexes, and most of them show reversible redox processes in solution. Also, many of the complexes reported here have been obtained as single crystals suitable for X-ray crystallography. Two of the complexes were further tested as phosphorescent dyes in OLED devices and showed high external quantum efficiencies (~7%) and color points better than the "standard" for blue iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C2']picolinate (FIrpic). We also report the full electrochemical investigation of FIrpic in different solvents.

Red, white, and blue: White light was obtained by partial energy transfer (∂ET) between a blue‐emitting IrIII–phenylpyridine complex and a red‐emitting EuIII–terpyridine chelate through excitation of the assembly that is formed from the two metal complexes (see picture).