Photophysical properties of fac-ReI(CO)3(pterin)(H2O) complex. Photochemically and thermally induced redox reactions.

FABRICIO RAGONE; PEDRO M. DAVID GARA; FERNANDO S. GARCÍA EINSCHLAG; ALEXANDER LAPPIN; GUILLERMO, FERRAUDI; EZEQUIEL WOLCAN; GUSTAVO T. RUIZ

Villa Carlos Paz

Congreso; XIII ELAFOT; 2017

In this work, we present a whole and deep study on the thermal redox and the photophysycal and photochemical reactions of a tricarbonyl Re(I) complex coordinating Ptr[1] (RePtr).The photophysical study of the RePtr complex realized in this work allowed to identify the nature and characteristics of its excited states. In addition, some intermediates and photo-products have been identified. In aqueous solutions, the complex fluorescence is attributed to the emitting 1IL state. In MeCN, however, the luminescence was ascribed to an interplay between 1IL and 3MLLCT states. The quantum fluorescence yield of the complex is much lower than its free ligand. This result is in good agreement with the theoretical calculations TD-DFT performed on the ligand and the complex, indicating a higher contribution of MLLCT than 1IL states to the electronic transitions that are populated by excitation at 350 nm.Flash photolyses results agreed, either in aqueous or MeCN solutions, helped to identify the naterure of the generated excited states. In aqueous solutions the 3IL state of Ptr in the Re-complex was detected. However, in MeCN solutions, flash photolyses experiments showed spectral features of the generated transients more consistent with the emitting 3MLCT. The deactivation of 3MLCT by O2 leads to the formation of 1O2 with a low quantum yield. No formation of 1O2 in D2O was detected, possibly due to a very low 3IL formation quantum yield. LIOAS spectroscopy confirmed that this complex released to the medium all the absorbed energy as prompt heat after laser excitation at 355 nm either in H2O and/or MeCN.The reduced transient spectrum generated by flash photolysis is in good agreement with the published spectra of the reduced ligand radical [2]. Pulse radiolysis experiments under oxidizing and/or reducing environments were performed in aqueous solutions of the Re complex. By performing an analysis by MCR-ALS, it was possible to identify the contribution of three species. The first intermediate was assigned, by spectral similarity, to the semireduced radical of the free ligand [3,4]. This spectrum also agrees with the spectrum found for the reduced transient generated by flash photolysis. The proposed reduction product is the complex Re(CO)3(7,8-PtrH2)(H2O). The oxidized transient spectrum was also obtained by pulse radiolysis, this compares very well with those published for ReII, leading us to propose oxidation in the metal core as the reaction product of the transient under oxidizing conditions.