Journal of Physical Chemistry A, Vol.120, No.24, 4131-4138, 2016
OFF-ON-OFF Dual Emission at Visible and UV Wavelengths from Carbazole Functionalized beta-Diketonate Europium(III) Complex
This work demonstrates dual emission "OFF-ON-OFF" switching at-visible and-UA, wavelengths of a carbazole functionalized beta-diketone (LH) by a simple change of a europium (III) ion (Eu3+) concentration in the submicromolar concentration range. In the presence of 0.25 equiv of Eu3+ (5 mu M), LH forms a luminescent 4:1 complex ([Eu3+(L-)(4)](-)) exhibiting dual emission at 357 and 613 nm resulting from the local excitation of the carbazole ring and ligand-sensitized luminescence from the Eu3+-beta-diketonate unit, respectively. The 4:1 complex begins to convert into a 2:1 complex ([Eu3+(L-)(2)](+)) via a 3:1 complex [Eu3+(L-)(3)] above a molar ratio ([Eu3+]/[LH]) of 0.25, which provides the opportunity for binding of solvent methanol molecules to the vacant site of the Eu3+ ion in the complex ([Eu3+(L-)(2)(MeOH)(n)](+)). The OH oscillators of coordinated methanol molecules facilitate the nonradiative pathway of the Eu3+ emission; hence the emission 613 nm almost disappears above the 0.50 equivalent of Eu3+ (11 mu M), while the UV emission at 357 nm remains mostly constant over the whole concentration range.