Theoretical Characterization of a Tridentate Photochromic Pt(II) Complex Using Density Functional Theory Methods
1School of Science, Penn State Erie, The Behrend College, 4205 College Drive, Erie, Pennsylvania 16563-0203.
Abstract:
Density functional theory methods have been used to characterize a tridentate photochromic Pt(II) complex [Pt(AAA)Cl], its acetonitrile complex [Pt(AAA)Cl·CH3CN], and the transition state in the complexation reaction. B3LYP/6-31G* (effective core potential for Pt) optimized geometries of Pt(AAA)Cl and Pt(AAA)Cl·CH3CN are found to be in reasonably good agreement with most of the applicable parameters for the available experimental crystal structures of Pt(AAA)Cl and a Pt(AAA)Cl-triphenylphoshine complex, with the exception of one of the dihedral angles, the deviation of which is determined to be due to a steric cis versus trans effect. Vibrational frequencies are calculated for Pt(AAA)Cl and cis-Pt(AAA)Cl·CH3CN, and the predicted shift in the benzaldehyde carbonyl frequency is found to be in line with that observed experimentally. Singlet vertical excitation energies are calculated for Pt(AAA)Cl and cis-Pt(AAA)Cl·CH3CN using time-dependent density-functional theory and are found to be in good agreement with the experimental transition energies, although for cis-Pt(AAA)Cl·CH3CN, the calculations suggest a reassignment of the experimental S1 and S2 transitions. Single point energies are calculated at the B3LYP/6-311+G(2d,2p) level (effective core potential for Pt) and the calculations predict the complexation reaction (dark reaction) to be exothermic and, after a correction to the entropy, to be exoergic at 298 K and to proceed with a reasonable activation energy. Based on singlet and triplet vertical excitation energies, it is speculated that the photoreaction occurs via an intersystem crossing from S1 to T1 for cis-Pt(AAA)Cl·CH3CN followed by an adiabatic reaction along the T1 surface and then nonradiative intersystem crossing to the S0 state of Pt(AAA)Cl.
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