Electronic structures and spectroscopic properties of self-assembled [Pt2M4(C≡CH)8](M=Cu,Ag) clusters have been studied by the TD-DFT(time-dependent density functional theory) calculations with the polarizable continuum model(PCM).The ground-and excited-state structures were optimized by the DFT(density functional theory) methods.The calculated structures and spectroscopic properties are in agreement with the corresponding experimental results.The [Pt2Ag4(C≡CH)8] clusters have two stable ground state geometries(D4 and D4h symmetry).The calculated Pt-M distances suggest only very weak interactions.The Cu-Cu distances are larger than the van der Waals radii of two Cu atoms and the Ag-Ag distances are analogous with the sum of van der Waals radii of two Ag atoms.Upon excitation,the interaction of Pt…M,Ag…Ag is strengthened,while the Cu…Cu distances are shortened but they are still larger than the sum of van der Waals radii of two Cu atoms.The lowest-energy absorptions are at 450,365 and 375 nm and the emissions are at 611,431 and 435 nm for [Pt2Cu4(C≡CH)8],[Pt2Ag4(C≡CH)8](A) and(B),respectively.The transitions are all perturbed by the Cu or Ag composition through the UV-Vis spectra region;therefore,there are not pure ILCT or MPtLCT characteristics(ILCT:intraligand charge transfer;MLCT:metal-to-ligand charge transfer) in absorptions of heteropolynuclear [Pt2M4(C≡CH)8] clusters.Since the emissions and the lowest-absorptions have different transition characteristics for each complex,the emissions should not come from the lowest-energy absorptions.Because the M…M interactions in the excited state of [Pt2Ag4(C≡CH)8] are augmented,the emissions of [Pt2Ag4(C≡CH)8] clusters bear prominent ILCT character,which is the reason why the emission wavelengths of [Pt2Ag4(C≡CH)8] have a small hypsochromic shift relative to the emission wavelength of homoleptic [Pt(C≡CH)4]2-precursor.
BAI FuQuan1,XIA BaoHui1,2,ZHANG HongXing1,YANG BaoZhu1,WANG Jian1 & SUN Lei1 1 State Key Laboratory of Theoretical and Computational Chemistry,Institute of Theoretical Chemistry,Jilin University,Changchun 130023,China
