Molecular geometry, electronic structure and optical properties study of meridianal tris(8-hydroxyquinolinato)gallium(III) with ab initio and DFT methods

Absorption and emission properties of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (M = Al, Ga, In) and correlations with molecular electrostatic potential

Substituent effect for a series of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (Mq3) of aluminum, gallium, and indium are investigated using density functional theory (DFT) for the ground state properties and the time-dependent version of DFT (TDDFT) for their absorption and emission properties. A comparison between the ground state energy of mer and fac isomers of all the complexes revealed that the mer configuration is always more stable than fac. The substituent effect is significantly reflected at the fluorescence maximum (λ_F ) values whereas the effect is moderate at the absorption maximum (λ_abs ) values. The molecular electrostatic potential (MESP) at the metal center (V_M ) and the most electron rich region indicated by MESP minimum (V_min ), located at the oxygen of phenoxide ring exhibit excellent correlations with the λ_F and Stokes shift (λ_F -λ_abs ) values. The study suggests the use of Stokes shift as an experimental quantity to measure the excited state substituent effect while the V_min or V_M emerge as theoretical quantities to measure the same.

Synthesis, characterization and DFT calculation of 4-fluorophenyl substituted tris(8-hydroxyquinoline)aluminum(III) complexes

New 4-fluorophenyl substituted 8-hydroxyquinoline derivatives, 5-(4-fluorophenyl)quinolin-8-ol and 5,7-bis(4-fluorophenyl)quinolin-8-ol, were synthesized and characterized by spectroscopic methods. The aluminum complexes of 5-(4-fluorophenyl)quinolin-8-ol (AlQF) and of 5,7-bis(4-fluorophenyl)quinolin-8-ol (AlQF2) exhibit strong fluorescence emission centered at 525 nm and 530 nm respectively. The quantum yield of both complexes were enhanced compared to the parent tris(8-hydroxyquinolinato)aluminum(III) complex. Electronic structures and photophysical properties of the new complexes were investigated theoretically by ab initio and density functional theory (DFT) and time dependent DFT (TD-DFT). Geometries of the ground state (S0) and the first excited state (S1) of the new complexes were optimized at the B3LYP/6-31G(d) functional and configuration interaction singles (CIS) method respectively. The aryl substituents were found to contribute significantly to the frontier molecular orbitals (FMOs). We have observed that in both cases the lowest occupied molecular orbital (LUMO) energy decreases while the energy of the highest occupied molecular orbital is slightly increased. The most significant increase was observed for AlQF2.

Combined effects of one 8-hydroxyquinoline/picolinate and "CH"/N substitutions on the geometry, electronic structure and optical properties of mer-Alq(3)

With the aim of evaluating the combined effect of one 8-hydroxyquinoline (q)/picolinate (p) and "CH"/N substitutions on the molecular geometry, electronic structure, and optical properties of tris-(8-hydroxyquinoline)aluminum [Alq(3)], the density functional theory (B3LYP) and time-dependent density functional theory (TD-B3LYP), using the 6-31G(d) and 3-21+G(d,p) basis sets were applied on Alq(3), Alq(2)p, and its "CH"/N-substitution derivatives. A comparison of the optimized ground-state (S(0)) geometries has shown that the molecular shape is conserved upon such a substitution. On the basis of the frontier molecular orbital and gap energy (E(g)) calculations, it was shown that, comparatively to the pristine Alq(2)p (and to the original parent Alq(3)), the HOMO and LUMO are stabilized, the net effect being an increasing or a decreasing E(g), depending on the position of the substituted group. The substitution of q(B) by p (from Alq(3) to Alq(2)p) was also found to induce the same feature. Starting from the S(0) and S(1) (first excited state) geometries, the effect of the substitution on the absorption (and emission) spectra was evaluated. It was found that the "CH"/N substitution in different positions on the two 8-hydroxyquinoline ligands may also constitute an efficient approach of tuning the Alq(2)p emitting color. In comparison with both Alq(3) and Alq(2)p, an important blue shift was predicted for the 5-substituted derivative, an important red shift being observed for the 4-substituted one. Also, relatively significant blue and red shifts were predicted for the 7- and 2-substituted derivatives. Finally, revisiting the correlation between the spectrum shifts and the metal-ligand bonding, our recent findings (2) were confirmed.

Optical Properties of the Phosphorescent Trinuclear Copper(I) Complexes of Pyrazolates: Insights from Theory

Theoretical investigations have been performed to explore the optical properties of {[3,5-(CF3)(2)Pz]Cu}3 in monomeric and dimeric forms using TD-DFT approaches. The emission of all complexes originates from the lowest triplet excited-states (T1), and the corresponding emissive states are assigned as the mixture of the metal-centered charge transfer and ligand-to-metal charge transfer. The features of the emission spectrum are clarified in detail. The bulk emission spectrum of complex is mainly determined by the stacked dimers rather than the individual monomers. The predicted maximum emission wavelength (lambda(em)) are in good agreement with experimental values, indicating that the phosphorescence bands can be assigned to two different conformations for the neighboring stacked dimers sharing the same monomer in the complex. Energy transfer from T1 of one stacked dimer to the neighboring one is responsible for the disappearance of the shoulder, leaving only the main peak upon heating. With the aim to reveal the conformational dependence for the triplet excited-state emission spectrum, the optical properties of various stacked dimers with different conformations are investigated by varying the relative arrangements through changing inter-monomer distance or rotational angles for the dimer which is responsible for the main peak emission. Calculation results suggest that the shortest intermolecular Cu...Cu distance plays an important role in the emission spectra of the vertical- and tilting-movement dimers, which is ascribed to the variation of the energy gap for the frontier molecular orbitals involved in the main emitting transition. The blue shift of lambda(em) in parallel-movement and rotational dimers can be traced back to the variation of the mutual spatial orientation. Therefore, the modulation of the extent of movement or rotational angles for stacked dimers by external perturbations creates new possibilities for the design of molecular light-emitting devices.