Photophysics and optical limiting of platinum(II) 4′-arylterpyridyl phenylacetylide complexes

A series of platinum(II) 4'-aryl-2,2':6',2-terpyridyl phenylacetylide complexes (5-8) with 4'-naphthyl, 4'-phenanthryl, 4'-anthryl, and 4'-pyrenyl substituents have been synthesized and characterized. The emission properties of these complexes and their corresponding platinum(II) 4'-aryl-2',2':6',2-terpyridyl chloride complexes (1-4) at room temperature and 77 K have been systematically investigated. Except for the 4'-pyrenyl-2,2':6',2-terpyridyl phenylacetylide complex that emits from an admixing state consisting of metaltoligand charge-transfer ((MLCT)-M-3), intraligand charge-transfer ((ILCT)-I-3), and (3)pi,pi* characters, emissions of 4'-naphthyl, 4'-phenanthryl, and 4'-anthryl-2,2':6',2-terpyridyl phenylacetylide complexes all originate from a (MLCT)-M-3-dominant state. The emission lifetime of the 4'-pyrenyl-2,2':6',2-terpyridyl phenylacetylide complex ( 8) is longer than 2 As at room temperature, and more than 300 As at 77 K, while the other three complexes possess an emission lifetime of 200-400 ns at room temperature and tens of microseconds at 77 K. Replacing the chloride ligand in the 4'-naphthyl, 4'-phenanthryl, and 4'-anthryl-2,2':6',2-terpyridyl chloride complexes by a phenylacetylide ligand significantly increases the emission efficiency by an order of magnitude, and the emission lifetimes become longer. In contrast, such an alternation has no pronounced effect on the emission efficiency and lifetime of the 4'-pyrenyl-2,2':6',2-terpyridyl complexes. In the transient difference absorption ( TA) spectra of 5 and 6, a moderately intense absorption band from 470 to 830 nm and a bleaching band between 400 and 470 nm were observed. For 7, the TA spectrum features a narrow, weak bleaching band at similar to 380 nm and a strong, narrow band at similar to 420 nm, as well as a broad, structureless band from 470 to 750 nm. In addition, a fourth, positive band appears above 800 nm. Complex 8 exhibits a strong, narrow bleaching band at similar to 340 nm and a broad, positive band extending from 370 to 830 nm, with the band maximum appearing at similar to 520 nm. The lifetimes obtained from the kinetic transient absorption measurement coincide with those from the kinetic emission measurement, indicating that the transient absorption originates from the same excited state that emits or, alternatively, from a state that is in equilibrium with the emitting state. All complexes exhibit optical limiting for 4.1 ns laser pulses at 532 nm, with 8 giving rise to the strongest optical limiting, presumably because of the much longer triplet excited-state lifetime and the stronger transient absorption at 532 nm.