| In recent years, metal complexes with specific structures were synthesized by therational designing and synthesis of novel organic ligands and the choice of the appropriatemetal ions, and then perform the investigation on the optical properties as well as therelationship between structures and optical properties, which has attracted the interest of anumber of research groups. Due to a variety of structures and luminescence properties havingthe potential for application to the molecular light-emitting devices, copper(I)-based systemsare of particular interest.Theoretical investigations are performed to explore the electronic structures and opticalproperties of {[3-(CF3),5-(Me)Pz]Cu}3 (1), {[3,5-(CF3)2Pz]Cu}3 (2) and {[3-(CF3),5-(Ph)Pz]Cu}3 (3) (Pz=pyrazole) using DFT approach. Electronic properties are calculated usingB3LYP/LANL2DZ, while the absorption and emission spectra are obtained using TD-B3LYPmethod with LANL2DZ and 6-31G basis sets, respectively. The maximum absorptionwavelengths are categorized as MCCT/MLCT (1), MLCT (2) and MLCT/LLCT (3). Theemission of all complexes originates from the lowest triplet excited-states, and thecorresponding emissive states are assigned as 3MCCT/3LMCT (1, 2), 3LMCT/3ILCT (3),respectively. With the aim to reveal the effect of the intermolecular Cu…Cu interaction on theabsorption and emission spectra, the electronic and optical properties of the dimers for 2 (2′and 2′′) are investigated. Neither intra-and intermolecular overlapping induced by the porbitals of Cu(I) nor intra-and intermolecular MCCT are found for the absorption of 2′and 2′′.The bulk absorption spectrum of complex 2 is mainly determined by the monomer rather thanthe dimers. The 663 and 590nm emission of 2 observed at 77K, agree with λem for 2′ and 2′′,respectively. Energy transfer from T1 of 2′′ to 2′ is responsible for the disappearance of theshoulder, leaving only the main peak of 2′ upon heating. For 2′, λem are dependent on thevariation of the energy difference (i.e. △E) for the orbitals involved in their main emittingstate assignments, while for 2′′, both main transition and the transition with smaller CIcoefficient contribute to the fininal λem. Furthermore, it can be seen from the orbital analysisthat there is only intramolecular overlapping induced by the p orbitals of Cu(I). Theintramolecular contribution to 3MCCT is much more than that of intermolecular one.We further investigate the triplet excited-state conformational dependency for the dimer2′ on the emission spectra at the same theory level, with the aim to understand the nature ofoptical characteristics. From this theoretical study, some light was shed on the conformationaleffect on the optical properties: (1) A red shift for λem was predicted with the shortestintermolecular Cu…Cu distance decreases for the slippage and vertical movement. (2) In thecase of the slippage and vertical movement, as the shortest intermolecular Cu…Cu distanceincreases, the change for λem can be simply traced back to the variation of △E which wascaused by the change of the ligand contributions for the virtual and occupied orbitals involvedin the main emitting transition. (3) The main emissive states for all dimers are assigned as3MCCT/3LMCT.
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