A theoretical density functional theory study has been performed on different families of cationic cyclometallated Ir(III) complexes with the general formula [Ir(C^N)2(N^N)](+) and azole-based ligands. The goal was to investigate the effect that the number and position of the nitrogen atoms of the azole ring have on the electronic structure and emission wavelength of the complex. The increase in the number of nitrogen atoms changes the relative energy of the HOMO and LUMO levels and leads to a gradual shift in the emission wavelength that can be larger than 100 nm. The direction of the shift however depends on the ligand in which the azole ring is introduced. The emission shifts to bluer wavelengths when the azole forms part of the cyclometallating C^N ligands, whereas it shifts to the red when the 5-membered ring is incorporated into the ancillary N^N ligand. The position of the nitrogen atoms in the azole ring also plays an important role in determining the emission energy. Complexes with phenyl-azole C^N ligands bearing a nitrogen in the azole position to which the phenyl is linked show a markedly blue-shifted emission compared to complexes with the same number of nitrogen atoms in the azole ring and bearing a carbon atom in that position. Therefore, when comparing the emission properties of azole-based [Ir(C^N)2(N^N)](+) complexes, not only the number of nitrogen atoms of the azole but also their position in the ring and the ligand where the azole ring is incorporated should be taken into account.
The association behavior of an electron-donating, bowl-shaped, truxene-based tetrathiafulvalene (truxTTF) with two corannulene-based fullerene fragments, ÀC 32 H 12 and C 38 H 14 À, is investigated in several solvents. Formation of 1:1 complexes is followed by absorption titrations and complemented by density functional theory (DFT) calculations. The binding constants are in the range log K a = 2.9-3.5. DFT calculations reveal that the most stable arrangement is the conformation in which the 1,3-dithiole ring of truxTTF is placed inside the concave cavity of the corannulene derivative. This arrangement is confirmed experimentally by NMR measurements, and implies that a combination of p-p and CH-p interactions is the driving force for association. Timedependent DFT calculations reproduce the experimental UV/ Vis titrations and provide a detailed understanding of the spectral changes observed. Femtosecond transient absorption studies reveal the processes occurring after photoexcitation of either C 32 H 12 or C 38 H 14 and their supramolecular associates with truxTTF. In the case of truxTTF·C 38 H 14 , photoexcitation yields the charge-separated state truxTTFC + ·C 38 H 14 C À with a lifetime of approximately 160 ps.
A simple model based on adjacency matrices is introduced to study the stability of hydrogenated polycyclic aromatic hydrocarbons. Aromaticity governs their relative stability having the most stable isomers the higher number of non-hydrogenated rings.
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