Transition excited-state properties

Stanton JF, Bartlett RJ (1993) The equation of motion coupled-cluster method - a systematic biorthogonal approach to molecular-excitation energies, transition-probabilities, and excited-state properties. J Chem Phys 98 7029... 

Excitation spectroscopy in a molecular beam is a powerful technique leading to more insight into the excited state properties of transition metal compounds. 

For the description of the linear and nonlinear optical properties of metallotetrapyrroles, TDDFT methods have proven [133-148] to be an excellent alternative to conventional highly correlated ab initio methods, such as SAC-CI, STEOM-CC, and CASPT2, for which these systems still represent a severe computational challenge, especially when transition metals, lanthanides or actinides are involved. The few highly correlated ab initio calculations dealing with the excited state properties of metallotetrapyrroles that have appeared to date only concern magnesium and zinc porphyrins and porphyrazines [149-151]. Application of TDDFT methods to the electronic spectroscopy of a variety of metallotetrapyrroles, including homoleptic and heteroleptic sandwiches, will be illustrated in this section. 

In two recent publications we have tried to characterize the excited state properties of 1 and 3 in order to facilitate their detection by LIF-spectroscopy. Our main tool in this effort has been equation of motion coupled cluster theory (EOM-CC). The EOM-CCSD method, which is equivalent to linear response CCSD, has been shown to provide an accurate description of both valence and excited states even in systems where electron correlation effects play an important role [39]. Computed transition energies for excitations that are of mainly single substitution character are generally accurate to within 0.1 eV. We have found the EOM-CCSD method to perform particularly well in combination with the doubly-augmented cc-pVDZ (d-aug-cc-pVDZ) basis set. This basis seems to provide equally balanced descriptions of ground and excited states,... 

This theory also possesses an ab initio based quantitative version (10,19), in which the parameters are geometry dependent and fitted on accurately calculated potential surfaces of ethylene. Despite its simplicity, the spin-Hamiltonian theory has proven itself to be accurate for predicting ground state, as well as excited state, properties and transition energies. 

EXCITED STATE PROPERTIES 14.3.1. Electronic Transitions of DNA Bases... 

Kunkely and Vogler reported on the excited state properties of [Cu(hfa)bta], with the absorption at 324 nm assigned to a spin-allowed Cu+ Jt bta MLCT transition. The solid state complex shows a broad emission band at 601 nm arising from MLCT. Besides, the photochemical behavior of this complex is in accordance with MLCT instead of LMCT. 

MLCT excited states have been the subject of a vast amount of research and literature. This section will attempt a general overview of the area. More detailed accounts can be found elsewhere [45, 47, 100-102]. The overwhelming majority of the published studies involve low-valent metals with polypyridyl ligands. In fact, any ligand with relatively low-energy LUMO s will give rise to such transitions. The general features of these transitions are not different from the IPCT and LMCT transitions discussed above. Excited-state properties can be different when 1) The... 

Polypyridine complexes of Fe(II) are strongly colored due to MLCT transitions. However, their MLCT excited states are very short-lived because of an efficient deactivation through lower-lying LF states. MLCT excited state lifetimes of [Fe(N,N)3] + range from 2.54 ns for tpy to 0.8 ns for bpy and phen [270]. Therefore, Fe complexes were deemed unsuitable for electron-transfer reactions. Recently, there is a renewed interest in excited state properties of Fe -polypyridines caused by the observation [304] of an ultrafast electron transfer from [Fe(4,4 -(COOH)2-bpy)2(CN)2] (tq = 330 ps) to Ti02, see Section 5.4.6. 

Coupled-Cluster Method. A Systematic Biorthogonal Approach to Molecular Excitation Energies, Transition Probabilities, and Excited State Properties. 

The excited state properties of trans-W(N2)2(dppe)2 were the focus of several recent spectroscopic [57-59] and photochemical studies [60-64]. The lowest energy excited state was assigned to a spin forbidden transition from a metal to dppe charge transfer (MLCT) excited state. All of the reported studies of the luminescence were carried out in glassy media (2-MeTHF). At temperatures between 8 and 80K, the spectra contain one apparent vibronic progression with a spacing of about 500cm [59]. 

The free ligand (65) exhibits intense 7r-7r transitions in the UV region, which decrease in intensity upon metal coordination. In these complexes, two or more subunits can be identified each with its own excited-state properties. In the Cu/Zn and Cu/Ag complex the 3LC state is quenched by the copper and by cobalt in the Cu/Co complex. Many related systems have been synthesized and their electrochemical and excited-state properties explored.190,191... 

Fig. 3.8 Schematic diagram for the orbitals of silicon quantum dots with different passivations. For absorption spectra, the electrons transit from the orbitals in the middle column to the orbitals in the right column [24]. Reprinted with permission from (Wang X, Zhang RQ, Niehaus TA, Frauen-heim T (2007) Excited state properties of allylamine-capped sihcon quantum dots, J Phys Chem C 111 2394-2400). Copyright (2007), American Chemici Society...

Ol must be incorporated in a correct treatment of transition matrix elements or excited-state properties. A useful way of eliminating this problem is to employ a commutator expression for the transition matrix element Oj]10>, where d is the transition operator. This form has the advantage of the reduction of operator rank due to the commutator. ... 

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