Theoretical (time-dependent DFT and MS-CASPT2) calculations showed that the two lowest-energy excited states of W(CO)5 complexes of 4-[(E)-2-carbomethoxy-2-cyanovinyl)]pyridine, 1 and 4-(2,2-dicyanovinyl)pyridine, 2 have metal-to-ligand charge transfer (MLCT) character. They result from an electron transfer from a tungsten-centered orbital (5dx2 − y2 or 5dxy) to the π* orbital localized on the ethylenic bridge. The calculated lowest excitation energy for 1 (537 nm) is close to the experimental value of 522 nm in cyclohexane. Laser flash photolysis at 532 nm in the nanosecond and picosecond domains showed that for both complexes transient excited states are formed with a quantum yield close to 1. Their lifetimes are about 10 times shorter than those observed previously for similar W(CO)5-pyridine complexes, with the lifetime of the excited state of compound 1 being longer than that of compound 2. Increasing the solvent polarity decreases the lifetimes in both cases. Complexes 1 and 2 are nonfluorescent, photostable, and do not undergo photosolvation.
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