Synthesis and Photophysics of Platinum(II) 6-Phenyl-4-(9,9-dihexylfluoren-2-yl)-2,2′-bipyridine Complexes with Phenothiazinyl Acetylide Ligand

Abstract

Two platinum 6-phenyl-4-(9,9-dihexylfluoren-2-yl)-2,2'-bipyridine complexes (4 and 5) with phenothiazinyl acetylide ligand were synthesized and characterized. Their UV-vis absorption and emission characteristics in solution and in Langmuir-Blodgett (LB) film were systematically investigated. The triplet transient difference absorption and nonlinear absorption properties were also studied for these complexes. Both complexes exhibit a broad metal-to-ligand charge transfer/intraligand charge transfer/ligand-to-ligand charge transfer ((1)MLCT/(1)ILCT/(1)LLCT) absorption band between 400 and 500 nm and a (3)MLCT/(3)ILCT/(3)pi,pi* emission band at approximately 594 nm at room temperature, which blue shifts at 77 K. Both UV-vis absorption and emission spectra show negative solvatochromic effect. The triplet excited-state lifetime at room temperature for complex 4 is approximately 1.2 micros, which is longer than that for complex 5 (approximately 600 ns). The emission quantum yield of complex 4 in toluene is 0.18 and 0.053 for complex 5. Both of the complexes also exhibit broad and moderately strong triplet transient absorption from the near-UV to the near-IR spectral region. However, 5 exhibits stronger reverse-saturable absorption than complex 4 does at 532 nm for nanosecond laser pulses. This is attributed to the weaker ground-state absorption but stronger triplet excited-state absorption at 532 nm for 5 than for 4, which leads to a larger ratio of excited-state absorption cross section to ground-state absorption for 5 than 4. In addition, LB films of 4 and 5 were prepared and characterized by AFM technique. The UV-vis absorption and emission spectra of the LB films of 4 and 5 were also investigated and compared with those obtained in solution.