Propylamino-connected fluorescent terpyridine dimer and trimer: syntheses, photophysical properties and formation of duplex-type complexes with Cd(ii)

Abstract

By using propylamine as a connector, a dimer (L2) and trimer (L3) of 2,2′:6′,2′′-terpyridine (tpy) are synthesized. They showed the lowest energy π–π* absorption at 354 nm and blue fluorescence at 420 nm with a moderate quantum yield in solution. Spectral titrations, electrospray ionization mass spectrometry (ESI-MS), ¹H–¹H rotating-frame nuclear Overhauser effect correlation spectroscopy (ROESY), and structure simulation (MOPAC/PM5) indicated that both L2 and L3 form duplex-type multi-component complexes with Cd(II), [Cd₂(L2)₂]⁴⁺ and [Cd₃(L3)₂]⁶⁺, respectively. While the luminescence of these complexes was quite weak in solution (quantum yield Φ < 0.005), the complexes showed enhanced emission in the solid state with remarkable increase of the quantum yield (Φ = 0.13).