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Theoretical Investigation of One- and Two-Photon Absorption Properties of Platinum Acetylide Chromophores

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journal contribution
posted on 01.12.2008, 00:00 by Zhao-Di Yang, Ji-Kang Feng, Ai-Min Ren
In this paper, we have theoretically investigated bis((4-phenylethynyl)phenyl) ethynyl)bis(trimethylphosphine)platinum(II) (PE2) and its analogsthree platinum acetylide complexes (13) that feature highly π-conjugated ligands (alkynyl-dimethylfluorene substituted with electron-donating or -withdrawing moieties). The geometrical and electronic structures are calculated at the ECP60MWB//6-31G*(H, C, P, N, S) basis set level by the density functional theory (DFT) method; one-photon absorption properties have been calculated by using time-dependent DFT (TDDFT) and Zernerʼs intermediate neglect of differential overlap (ZINDO) methods, and two-photon absorption (TPA) properties are obtained with the ZINDO/sum-over-states method. The values of βsp and βd for Pt are adjusted to −1 eV and −28.5 eV, respectively, to make one-photon absorption spectra calculated by ZINDO closest to the experimental data and TDDFT results. The calculated results indicate that all molecules in this work (involving cis isomers of molecules 13) take on two TPA peaks in the 600−800 nm region. The peak at 700−750 nm should not be simply attributed to the appearance of noncentrosymmetric cis isomers in solution, although trans and cis isomers adhere to a different selection rule. Every TPA peak results from its transition character. Molecules 13 show greater two-photon absorption strength compared with PE2 and retain good transparency.