Absorption and emission spectroscopy of a new water-soluble tricarbonyl Re(I) complex. Solvent and pH dependence.

FABRICIO RAGONE; ANDRÉS THOMAS; FERNANDO S. GARCÍA EINSCHLAG; GUSTAVO T. RUIZ

Conferencia; 21st I-APS Conference. Inter-American Photochemical Society; 2011

A new ReI(CO)3L1L2 complex has been obtained and characterized by Rx, 1H-RMN, IR, UV-MALDI and ESI. The ligand L1 = 2-amine-4-pteridinone, pterin, is a heterocyclic compound of biological interest and L2 = H2O. Here we show preliminary results about spectroscopy´s studies of solutions of the complex in different solvents and pH´s. UV-Vis absorption spectra show intense bands in the UV range, lmáx ~ 345 nm. These spectral features are almost identical with those found in the electronic spectrum of the free pterin ligand and are therefore assigned to p-p* excitations in the aromatic ligand fragment. The solutions of complex are coloured and their absorption in the visible part of the spectrum exhibit typically intense and solvatochromic long-wavelength metal-to-ligand charge transfer (MLCT) transitions from the metal dp to the lowest lying ligand p* orbital. These bands experience an hypsochromic shift with increasing solvent polarity, feature that confirms this assignment. The strong dependence on pH suggests the existence of two acid-base equilibrium. Emission spectra in aqueous solutions of the complex show the luminescence which was attributed to a desactivation from the lower p-p* ligand-localized state, as suggested from the emission spectrum of the free pterin. However, the emission from IL and MLCT excited states have been observed in organic solvent. Moreover, the observed luminescence shows a strong dependence on oxygen concentration. The calculated values for both emission quantum yield and lifetime in all solvents tested will be compared with those reported to free pterins. These photophysics properties lead us to believe in this kind of complex to be used in the development of new photochemical sensors.