Cyclometalated Ir(III) Complexes with Curcuminoid Ligands as Active Second-Order NLO Chromophores and Building Blocks for SHG Polymeric Films

Abstract

The second-order nonlinear optical (NLO) properties of iridium(III) complexes having two cyclometalated 2-phenylpyridines and curcumin or tetrahydrocurcumin as ancillary ligand have been investigated both in solution and as guest in a polymeric organic matrix. In solution, these complexes are characterized by a significant second-order NLO response, as determined by the Electric Field Induced Second Harmonic (EFISH) technique, like the related complex with acetylacetonate. Whereas the low second-harmonic generation response of a composite film of [Ir(2-phenylpyridine)2(acetylacetonate)] in polymethyl methacrylate was not stable and fell down to zero upon turning off the electric field. A good and stable response was obtained with a film based on the iridium(III) complex bearing two cyclometalated 2-phenylpyridines and curcumin.

Correlation between Second Ionization Potential and Nonlinear Optical Properties of Bivalent Transition-Metal Complexes: A Quantum Chemical Study

“…Complex Structures. The geometries of complexes FeL 5 and PtL 1 were DFT-optimized and are illustrated in Figure 1, whereas calculated bond lengths and angles of M(II)L i (M = Mn, Tc, Re, Co, Ni, Pd, Pt, Cu, Zn, Cd, and Hg, i = 1 and 5, and for Fe, Ru, and Os, i = 1 to 6) are summarized in Tables S2−S6 (see Supporting Information). In given complexes ML i , the M(II) metal center is pseudooctahedrally surrounded by the hexadentate pyridine amide ligand, the singlet Pd(II) and Pt(II) excepted, which present a distorted square-planar coordination (Figure 1).…”

“…The most stable spin state for the ReL i and TcL i (i = 1 and 5) is LS, and the energy difference between sextet spin state (HS) and doublet spin state (LS) is about 1.48 eV for ReL 1 and TcL 1 and 2.6 eV for ReL 5 and TcL 5 complexes. On the other hand, for the MnL i complexes, the most stable spin state is the sextet (see Tables 1 and S1 in Supporting Information).…”

“…The Mulliken charge of the metal ions, the ligand atoms which coordinated to them, and geometry parameters computed for ML i (i = 1 and 2; M = Mn, Re, Tc, Fe, Ru, Os, and Co) in HS and LS states are listed in Table S7. The analysis of these results shows that the HS state of MnL 5 , FeL 5 , CoL 5 , and RuL 5 complexes has larger metal−ligand bond length than the LS (about +0.21, +0.18, +0.10, and +0.09 Å, respectively), as expected. They have also much larger Mulliken charge of TM atoms and corresponding coordinated atoms, as compared to the LS state.…”

“…On the other hand, to provide a high NLO response, the coordination complex with the πconjugated ligand should be asymmetric, and it should possess low-energy absorption with charge-transfer transitions, whereas the difference between the excited-state and the ground-state dipole moment should be large. 5 The bonding model of transition-metal (TM) complexes can explain many important properties of the TM complexes including their magnetism, structures, stability, oxidation state, reactivity, and optical (linear and nonlinear) properties. It is to be noted that in the TM complexes, the energies of the five (n − 1) d orbitals of the TM ion are affected by the nature of the ligands (strong or weak field).…”

“…Also in this study, we focused on two series of TM complexes, ML 1 and ML 5 , because we benefit from an abundance of the experimental data (X-ray crystallography, UV−vis spectra...). 10,11,13−16 On the other hand, the L 1 and L 5 ligands have different rings and spacer groups (pyridine/ pyrazine and amide/thioether, respectively), so that both effects can be identified in analyzing the role of TM atoms in the NLO responses for the two different series.…”