Akademik Veri Yönetim Sistemi
INORGANIC CHEMISTRY, cilt.58, sa.3, ss.1850-1861, 2019 (SCI-Expanded)
Using naphthalimide (NI), complexes (Pt-PhNI and Pt-PhMeNI) based on the N<^>N platinum(II) bis(phenylacetylide) coordination framework were prepared, in which there are two close-lying triplet states, i.e., the metal-to-ligand-charge-transfer ((MLCT)-M-3) and the NI localized emissive state ((LE)-L-3). Pt-PhNI has better electronic communication between the Pt coordination center and the NI moiety, whereas in Pt-PhMeNI, they are more isolated by orthogonal geometry. For Pt-PhMeNI, the S-0 -> (MLCT)-M-1 and S-0 -> (LE)-L-1 absorption bands are separated by 5655 cm(-1), while they are more overlapped in Pt-PhNI. The (MLCT)-M-3 -> S-0 and (LE)-L-3 -> S-0 dual phosphorescence emissions were observed for both Pt-PhNI (in toluene) and Pt-PhMeNI (in benzonitrile). The molecular conformation tunes the (MLCT)-M-3/(LE)-L-3 state population ratio, and the orthogonal geometry makes the (LE)-L-3 state in Pt-PhMeNI basically a dark state (in toluene). Switching of the relative energy levels of the (MLCT)-M-3/(LE)-L-3 states by variation of the solvent polarity and temperature was achieved. For Pt-PhMeNI, the energy level of (MLCT)-M-3 state is higher in a polar solvent; thus, the (MLCT)-M-3 emission decreases, while the phosphorescence lifetime is prolonged from 9.5 mu s (in toluene) to 58 mu s (in benzonitrile) because of the different equilibria with the nonemissive (LE)-L-3 state. Conversely, increasing the temperature enhances the upward transition from the nonemissive (LE)-L-3 state to the emissive (MLCT)-M-3 state; as such, the phosphorescence of Pt-PhMeNI was intensified at higher temperature (which is unusual), and the phosphorescence lifetime decreased from 58 mu s (298 K) to ca. 5 mu s (348 K). The ultrafast intersystem crossing (ca. 0.5 ps) and intramolecular triplet-triplet energy transfer (3-11 ps) were studied by femtosecond transient absorption spectroscopy. These results are useful for an in-depth understanding of the photophysics of multichromophore transition-metal complexes and for the design of external stimuli-responsive sensing materials, for instance, temperature or microenvironment sensing materials.