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Coordination of 4'-(C6H4-p-X)-2,2':6',2'-terpyridines[X = NO2, NBu2, (E)-CH=CH-C6H4-p-NBu2, (E,E)-(CH=CH)2-C6H4-p-NMe2] to Zn(II), Ru(III), and Ir(III) metal centers induces a significant enhancement of the absolute value of their second-order nonlinear optical (NLO) response. Varying the nature of the metal center, the second order NLO response shifts from positive to negative, being controlled by metal-to-ligand, ligand-to-metal or intraligand charge-transfer transitions.

The synthesis and characterization of highly phosphorescent blue-light-emitting anionic iridium complexes are described. Density functional theory (DFT) and time dependent-DFT calculations are performed on the ground and excited states of these complexes in order to provide insights into the structural electronic and optical properties of these systems.

A combined experimental and theoretical study on cationic Ir(III) complexes for organic light-emitting diodes (OLED) applications and a strategy to tune the phosphorescence wavelength and to enhance the emission quantum yields for this class of compounds is described. The results have shown that functionalization of the bpy ligand by electron-donating substituents has achieved the objective of shifting the emission energy toward the blue-region of the spectrum, reducing, at the same time, the nonradiative decay pathways.

A combined density functional theory (DFT)/time-dependent density functional theory (TDDFT) study of the geometry, electronic structure and absorption and emission properties of the tetranuclear 'cubane' [Cu.sub.4][I.sub.4][py.sub.4] (py = pyridine) system is presented. The results have shown that while at the ground-state geometry the halide-to-pyridine charge-transfer excited state (XLCT) has a lower energy than the triplet Cu-I cluster-centered [super 3]CC excited state, the strong geometrical relaxation on the [super 3]CC state surface leads to a reverse order of the excited states in emission.

The reactivity of the isomeric oxo-Mn(V)-2-tetra-N-methylpyridyl (2-TMPyP) and oxo-Mn(V)-4-tetra-N-methylpyridyl (4-TMPyP) porphyrins has been investigated by a combined experimental and theoretical approach based on density functional theory. The unusual higher reactivity of the more electron-rich 4-TMPyP species appears to be related to both the higher basicity of its oxo ligand, compared to that of the 2-TMPyP isomer, and the smaller low-spin-high-spin promotion energy of 4-TMPyP, compared to that of 2-TMPyP, because of the stabilization of the A2u orbital in the latter isomer. Therefore, in a two-state energy profile involving crossing of the initial singlet and final quintet potential energy surfaces, the 4-TMPyP isomer should be kinetically favored. The calculated differences in the singlet-quintet gaps for the 2-TMPyP and 4-TMPyP systems compare well with the measured differences in the activation energies for two isomeric porphyrins. Both effects, proton affinity and electron-promotion energy, contribute to reduce the reactivity of the more electrophilic oxidant when electron-withdrawing groups are closer to the active site, contrary to the usual expectations based on simple chemical reactivity correlations. These theoretical results are in accord with new experimental data showing OMn(V)OH pKa5 of 7.5 and 8.6 for the isomeric 2-TMPyP and 4-TMPyP systems, respectively. [ABSTRACT FROM AUTHOR]

The manganese-oxo ‘cubane’ core complex Mn4O4L¹6 (1, L¹ = Ph2PO2-), a partial model of the photosynthetic water oxidation site, was shown previously to undergo photodissociation in the gas phase by releasing one phosphinate anion, an O2 molecule, and the intact butterfly core cation (Mn4O2L¹5+). Herein, we investigate the photochemistry and electronic structure of a series of manganese-oxo cubane complexes: [Mn4O4L²6] (2), 1+(ClO4-), 2+(OlO4-), and Mn4O3(OH)L¹6 (1H). We report the atomic structure of [Mn4O4L²6](ClO4), 2+(OlO4-) [L² = (4-MeOPh)2PO2-]. UV photoexcitation of a charge-transfer band dissociates one phosphinate, two core oxygen atoms, and the Mn4O2L5+ butterfly as the dominant (or exclusive) photoreaction of all cubane derivatives in the gas phase, with relative yields: 1H » 2 > 1 > 2+ > 1+. The photodissociation yield increases upon (1) reducing the core oxidation state by hydrogenation of a corner oxo (1H), (2) increasing the electron donation from the phosphinate ligand (L²), and (3) reducing the net charge from +1 to O. The experimental Mn-O bond lengths and Mn-O bond strengths and the calculated ligand binding energy explain these trends in terms of weaker binding of phosphinate L² versus L¹ by 14.7 kcal/mol and stronger Mn-(μ–-O)(core) bonds in the oxidized complexes 2+ and 1+ versus 2 and 1. The calculated electronic structure accounts for these trends in terms of the binding energy and antibonding Mn-O(core) and Mn-O′(ligand) character of the degenerate highest occupied molecular orbital (HOMO), including (1) energetic destabilization of the HOMO of 2 relative to 1 by 0.75 eV and (2) depopulation of the antibonding HOMO and increased ionic binding in 1+ and 2+ versus 1 and 2. [ABSTRACT FROM AUTHOR]

The role of chlorine doping in CH 3 NH 3 PbI 3 represents an important open issue in the use of hybrid perovskites for photovoltaic applications. In particular, even if a positive role of chlorine doping on perovskite film formation and on material morphology has been demonstrated, an inherent positive effect on the electronic and photovoltaic properties cannot be excluded. Here we carried out periodic density functional theory and Car-Parrinello molecular dynamics simulations, going down to ∼1% doping, to investigate the effect of chlorine on CH 3 NH 3 PbI 3 . We found that such a small doping has important effects on the dynamics of the crystalline structure, both with respect to the inorganic framework and with respect to the cation libration motion. Together, we observe a dynamic spatial localization of the valence and conduction states in separated spatial material regions, which takes place in the 10 -1 ps time scale and which could be the key to ease of exciton dissociation and, likely, to small charge recombination in hybrid perovskites. Moreover, such localization is enhanced by chlorine doping, demonstrating an inherent positive role of chlorine doping on the electronic properties of this class of materials.

The manganese-oxo "cubane" core complex Mn(4)O(4)L(1)(6) (1, L(1) = Ph(2)PO(2-)), a partial model of the photosynthetic water oxidation site, was shown previously to undergo photodissociation in the gas phase by releasing one phosphinate anion, an O(2) molecule, and the intact butterfly core cation (Mn(4)O(2)L(1)(5+)). Herein, we investigate the photochemistry and electronic structure of a series of manganese-oxo cubane complexes: [Mn(4)O(4)L(2)(6)] (2), 1(+)(ClO(4-)), 2(+)(ClO(4-)), and Mn(4)O(3)(OH)L(1)(6) (1H). We report the atomic structure of [Mn(4)O(4)L(2)(6)](ClO(4)), 2(+)(ClO(4-)) [L(2) = (4-MeOPh)(2)PO(2-)]. UV photoexcitation of a charge-transfer band dissociates one phosphinate, two core oxygen atoms, and the Mn(4)O(2)L(5)(+) butterfly as the dominant (or exclusive) photoreaction of all cubane derivatives in the gas phase, with relative yields: 1H >> 2 > 1 > 2(+) > 1(+). The photodissociation yield increases upon (1) reducing the core oxidation state by hydrogenation of a corner oxo (1H), (2) increasing the electron donation from the phosphinate ligand (L(2)), and (3) reducing the net charge from +1 to 0. The experimental Mn-O bond lengths and Mn-O bond strengths and the calculated ligand binding energy explain these trends in terms of weaker binding of phosphinate L(2) versus L(1) by 14.7 kcal/mol and stronger Mn-(mu(3)-O)(core) bonds in the oxidized complexes 2(+) and 1(+) versus 2 and 1. The calculated electronic structure accounts for these trends in terms of the binding energy and antibonding Mn-O(core) and Mn-O'(ligand) character of the degenerate highest occupied molecular orbital (HOMO), including (1) energetic destabilization of the HOMO of 2 relative to 1 by 0.75 eV and (2) depopulation of the antibonding HOMO and increased ionic binding in 1(+) and 2(+) versus 1 and 2.