title: Modulation of Intersystem Crossing Rate by Minor Ligand Modifications in Cyclometalated Platinum(II) Complexes.
abstract: Photophysical properties of four new platinum(II) complexes comprising extended ppy (Hppy = 2-phenylpyridine) and thpy (Hthpy = 2-(2'-thienyl)pyridine) cyclometalated ligands and acetylacetonate (acac) are reported. Substitution of the benzene ring of Pt-ppy complexes 1 and 2 with a more electron-rich thiophene of Pt-thpy complexes 3 and 4 leads to narrowing of the HOMO-LUMO gap and thus to a red shift of the lowest energy absorption band and phosphorescence band, as expected for low-energy excited states of the intraligand/metal-to-ligand charge transfer character. However, in addition to these conventional spectral shifts, another, at first unexpected, substitution effect occurs. Pt-thpy complexes 3 and 4 are dual emissive showing fluorescence about 6000 cm(-1) (∼0.75 eV) higher in energy relative to the phosphorescence band, while for Pt-ppy complexes 1 and 2 only phosphorescence is observed. For dual-emissive complexes 3 and 4, ISC rates kISC are estimated to be in order of 10(9)-10(10) s(-1), while kISC of Pt-ppy complexes 1 and 2 is much faster amounting to 10(12) s(-1) or more. The relative intensities of the fluorescence and phosphorescence signals of Pt-thpy complexes 3 and 4 depend on the excitation wavelength, showing that hyper-intersystem crossing (HISC) in these complexes is observably significant.
authors.affiliation: Ural Federal University , Mira 19, Ekaterinburg, 620002, Russia.|I. Postovsky Institute of Organic Synthesis , Ekaterinburg, 620041, Russia.
authors.forename: Marsel Z
authors.initials: MZ
authors.lastname: Shafikov
authors.affiliation: Ural Federal University , Mira 19, Ekaterinburg, 620002, Russia.
authors.forename: Dmitry N
authors.initials: DN
authors.lastname: Kozhevnikov
authors.forename: Michael
authors.initials: M
authors.lastname: Bodensteiner
authors.forename: Fabian
authors.initials: F
authors.lastname: Brandl
authors.forename: Rafał
authors.initials: R
authors.lastname: Czerwieniec