Two-Degree-of-Freedom Controller Tuning

Two-degree-of-freedom controllers have the ability to affect the dynamics of a system when the reference value changes. The answer to the question of parameter tuning for this additional lter still remains unclear we describe a new method for the design of said controller. We compare the behaviour of the controllers designed using the presented method versus the classic method on several instances

Two-Degree-of-Freedom Controller Tuning

Two-degree-of-freedom controllers have the ability to affect the dynamics of a system when the reference value changes. The answer to the question of parameter tuning for this additional lter still remains unclear we describe a new method for the design of said controller. We compare the behaviour of the controllers designed using the presented method versus the classic method on several instances.</jats:p

Excited states of nitro-polypyridine metal complexes and their ultrafast decay. Time-resolved IR absorption, spectroelectrochemistry, and TD-DFT calculations of fac-[Re(Cl)(CO)3(5-Nitro-1,10-phenanthroline)]

The lowest absorption band of fac-[Re(Cl)(CO)(3)(5-NO2-phen)] encompasses two close-lying MLCT transitions. The lower one is directed to LUMO, which is heavily localized on the NO2 group. The UV-vis absorption spectrum is well accounted for by TD-DFT (G03/PBEPBE1/CPCM), provided that the solvent, MeCN, is included in the calculations. Near-UV excitation of fac-[Re(Cl)(CO)(3)(5-NO2-phen)] populates a triplet metal to ligand charge-transfer excited state, (MLCT)-M-3, that was characterized by picosecond time-resolved IR spectroscopy. Large positive shifts of the v(CO) bands upon excitation (+70 cm(-1) for the A'(1) band) signify a very large charge separation between the Re(Cl)(CO)3 unit and the 5-NO2-phen ligand. Details of the excited-state character are revealed by TD-DFT calculated changes of electron density distribution. Experimental excited-state v(CO) wavenumbers agree well with those calculated by DFT. The (MLCT)-M-3 state decays with a ca. 10 ps lifetime (in MeCN) into another transient species, that was identified by TRIR and TD-DFT calculations as an intraligand (3)n pi* excited state, whereby the electron density is excited from the NO2 oxygen lone pairs to the pi* system of 5-NO2-phen. This state is short-lived, decaying to the ground state with a similar to 30 ps lifetime. The presence of an n pi* state seems to be the main factor responsible for the lack of emission and the very short lifetimes of 3 MLCT states seen in all d(6)-metal complexes of nitro-polypyridyl ligands. Localization of the excited electron density in the lowest (MLCT)-M-3 states parallels localization of the extra electron in the reduced state that is characterized by a very small negative shift of the v(CO) IR bands (-6 cm(-1) for A'(1)) but a large downward shift of the v(s)(NO2) IR band. The Re-Cl bond is unusually stable toward reduction, whereas the Cl ligand is readily substituted upon oxidation

Ultrafast Photochemical Dissociation of an Equatorial CO Ligand from <i>trans(X,X)</i>-[Ru(X)₂(CO)₂(bpy)] (X = Cl, Br, I): A Picosecond Time-Resolved Infrared Spectroscopic and DFT Computational Study

Ultrafast photochemistry of the complexes trans(X,X)-[Ru(X)2(CO)2(bpy)] (X = Cl, Br, I) was studied in order to understand excited-state reactivity of equatorial CO ligands, coordinated trans to the 2,2‘-bipyridine ligand (bpy). TD-DFT calculations have identified the lowest electronic transitions and singlet excited states as mixed X → bpy/Ru → bpy ligand to ligand/metal to ligand charge transfer (LLCT/MLCT). Picosecond time-resolved IR spectroscopy in the region of ν(CO) vibrations has revealed that, for X = Cl and Br, subpicosecond CO dissociation is accompanied by bending of the X−Ru−X moiety, producing a pentacoordinated intermediate trans(X,X)-[Ru(X)2(CO)(bpy)]. Final movement of an axial halide ligand to the vacant equatorial position and solvent (CH3CN) coordination follows with a time constant of 13−15 ps, forming the photoproduct cis(X,X)-[Ru(X)2(CO)(CH3CN)(bpy)]. For X = I, the opticaly populated 1LLCT/MLCT excited state undergoes a simultaneous subpicosecond CO dissociation and relaxation to a triplet IRuI-localized excited state which involves population of an orbital that is σ-antibonding with respect to the axial I−Ru−I bonds. Vibrationally relaxed photoproduct cis(I,I)-[Ru(I)2(CO)(CH3CN)(bpy)] is formed with a time constant of ca. 55 ps. The triplet excited state is unreactive, decaying to the ground state with a 155 ps lifetime. The experimentally observed photochemical intermediates and excited states were assigned by comparing calculated (DFT) and experimental IR spectra. The different behavior of the chloro and bromo complexes from that of the iodo complex is caused by different characters of the lowest triplet excited states

Excited-State Characters and Dynamics of [W(CO)₅(4-cyanopyridine)] and [W(CO)₅(piperidine)] Studied by Picosecond Time-Resolved IR and Resonance Raman Spectroscopy and DFT Calculations: Roles of W → L and W → CO MLCT and LF Excited States Revised

The characters, dynamics, and relaxation pathways of low-lying excited states of the complexes [W(CO)5L] [L = 4-cyanopyridine (pyCN) and piperidine (pip)] were investigated using theoretical and spectroscopic methods. DFT calculations revealed the delocalized character of chemically and spectroscopicaly relevant molecular orbitals and the presence of a low-lying manifold of CO π*-based unoccupied molecular orbitals. Traditional ligand-field arguments are not applicable. The lowest excited states of [W(CO)5(pyCN)] are W → pyCN MLCT in character. They are closely followed in energy by W → CO MLCT states. Excitation at 400 or 500 nm populates the 3MLCT(pyCN) excited state, which was characterized by picosecond time-resolved IR and resonance Raman spectroscopy. Excited-state vibrations were assigned using DFT calculations. The 3MLCT(pyCN) excited state is initially formed highly excited in low-frequency vibrations which cool with time constants between 1 and 20 ps, depending on the excitation wavelength, solvent, and particular high-frequency ν(CO) or ν(CN) mode. The lowest excited states of [W(CO)5(pip)] are W → CO MLCT, as revealed by TD-DFT interpretation of a nanosecond time-resolved IR spectrum that was measured earlier in a low-temperature glass (Johnson, F. P. A.; George, M. W.; Morrison, S. L.; Turner, J. J. J. Chem. Soc., Chem. Commun. 1995, 391−393). MLCT(CO) excitation involves transfer of electron density from the W atom and, to a lesser extent, the trans CO to the π* orbitals of the four cis CO ligands. Optical excitation into MLCT(CO) transition of either complex in fluid solution triggers femtosecond dissociation of a W−N bond, producing [W(CO)5(solvent)]. It is initially vibrationally excited both in ν(CO) and anharmonicaly coupled low-frequency modes. Vibrational cooling occurs with time constants of 16−22 ps while the intramolecular vibrational energy redistribution from the v = 1 ν(CO) modes is much slower, 160−220 ps. No LF excited states have been found for the complexes studied in a spectroscopically relevant range up to 6−7 eV. It follows that spectroscopy, photophysics, and photochemistry of [W(CO)5L] and related complexes are well described by an interplay of close-lying MLCT(L) and MLCT(CO) excited states. The high-lying LF states play only an indirect photochemical role by modifying potential energy curves of MLCT(CO) states, making them dissociative

Ligand-to-Diimine/Metal-to-Diimine Charge-Transfer Excited States of [Re(NCS)(CO)₃(α-diimine)] (α-diimine = 2,2‘-bipyridine, di-ⁱPr-<i>N,N</i>-1,4-diazabutadiene). A Spectroscopic and Computational Study

Two new complexes fac-[Re(NCS)(CO)3(N,N)] (N,N = 2,2‘-bipyridine (bpy), di-iPr-N,N-1,4-diazabutadiene (iPr-DAB)) were synthesized and their molecular structures determined by X-ray diffraction. UV−vis absorption, resonance Raman, emission, and picosecond time-resolved IR spectra were measured experimentally and calculated with TD-DFT. A good agreement between experimental and calculated ground- and excited-state spectra is obtained, but only if the solvent (MeCN) is included into calculations and excited state structures are fully optimized at the TD-DFT level. The lowest excited states of the bpy and iPr-DAB complexes are assigned by TD-DFT as 3aA‘ by comparison of calculated and experimental IR spectra. Excited-state lifetimes of 23 ns and ca. 625 ps were determined for the bpy and DAB complex, respectively, in a fluid solution at room temperature. Biexponential emission decay (1.3, 2.7 μs) observed for [Re(NCS)(CO)3(bpy)] in a 77 K glass indicates the presence of two unequilibrated emissive states. Low-lying electronic transitions and excited states of both complexes have a mixed NCS → N,N ligand-to-ligand and Re → N,N metal-to-ligand charge-transfer character (LLCT/MLCT). It originates in mixing between Re dπ and NCS π characters in high-lying occupied MOs. Experimentally, the LLCT/MLCT mixing in the lowest excited state is manifested by shifting the ν(CO) and ν(NC) IR bands to higher and lower wavenumbers, respectively, upon excitation. Resonant enhancement of both ν(CO) and ν(NC) Raman bands indicates that the same LLCT/MLCT character mixing occurs in the lowest allowed electronic transition