Theoretical Investigation of One- and Two-Photon Absorption Properties of Platinum Acetylide Chromophores
journal contributionposted 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 analogsthree platinum acetylide complexes (1−3) 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 1−3) 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 1−3 show greater two-photon absorption strength compared with PE2 and retain good transparency.