Excited-State Absorption of 4'-(5'''-R-PYRIMIDYL)-2,2':6',2''- Terpyridyl Platinum(II) Phenylacetylide Complexes (Preprint)

摘要

The singlet excited-state absorption of five 4'-(5'''-R-pyrimidyl)-2, 2':6',2/1-terpyridyl platinum(II) phenylacetylide complexes were investigated using fs pump-probe UV-Vis spectroscopy. These complexes exhibit broad, moderately intense S1-Sn absorption from 500 to 800 nm, which could be attributed to the 1MLCT state. The S1-Sn absorption band energy is influenced by the substituent on the 5'''-position of the pyrimidyl ring, with an electron- donating substituent increasing the energy, and electron-withdrawing substituent decreasing it. The singlet excited-state lifetime deduced from the decay of the fs transient absorption is in the range of 37 -139 ps. Open- aperture Z-scan experiments using ns and ps lasers at 532 nm for 1-5 were carried out in CH3CN solutions and the wavelength dispersion characteristics of 1 was investigated using ps laser at various wavelengths. Reverse saturable absorption (RSA) is observed for all complexes at 532 nm for both ns and ps Z scans, and RSA occurs at 500 -600 nm for 1 for ps laser. Fitting of the experimental Z-scan data using a five-level dynamic model gives rise to the quantitative singlet and triplet excited-state absorption cross-sections, which varies from (18 =/- 1)x 10(exp-18) sq cm to (50+/-5)x10(exp-18) sq cm for sigmas and (11+/-1)x10(exp-18) sq cm to (14+/-2)x10(exp-18) sq cm for sigmaT at 532 nm, corresponding to a ratio of 6.5 -29.8 for sigmas/sigmag and 2.8 -11.2 for sigmaT/sigmag for 1-5. Complexes 1, 2 and 4 exhibit a much larger sigmas/sigmag compared to those of 3 and 5. Moreover, the sigmas/sigmag ratio increases from 1.9 at 500 nm to 260 at 600 nm for complex 1.