Synthesis and photophysical properties of cyclometalated 4′-phenyl-2,2′:6′,2″-terpyridyl Pt(II) chloride complexes with different aryl substituents

A series of 4′-phenyl-2,2′:6′,2″-terpyridyl Pt(II) chloride complexes bearing different aryl substituents (1a–1f) was designed and synthesized. The photophysical properties of these complexes have been systematically investigated. All complexes exhibit strong ¹π,π* absorption bands in the UV region; and broad, structureless metal-to-ligand charge transfer (¹MLCT) absorption bands in the visible region. When excited at the charge-transfer absorption band, the complexes exhibit room temperature luminescence (λ_em = 555–614 nm) in CH₃CN. The emissions of complexes 1c–1f with electron-donating or extended π-conjugation substituents are assigned to the ³MLCT states. Meanwhile, the emitting state of 1a and 1b exhibits a significant intraligand ³π,π* character. Complexes 1a–1d exhibit moderate triplet transient absorptions from visible to NIR region, where reverse saturable absorption (RSA) occurs. Their photophysical properties have been investigated with the aim to provide a basis for elucidating the structure-property correlations and developing new nonlinear optical materials.