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

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

Congreso; XIII ELAFOT; 2017

In this work, we present a whole and deepstudy on the thermal redox and the photophysycal and photochemical reactions ofa tricarbonyl Re(I) complex coordinating Ptr[1] (RePtr).The photophysical study of the RePtr complex realized in thiswork allowed to identify the nature and characteristics of its excited states.In addition, some intermediates and photo-products have been identified. Inaqueous solutions, the complex fluorescence is attributed to the emitting 1ILstate. In MeCN, however, the luminescence was ascribed to an interplay between 1ILand 3MLLCT states. The quantum fluorescence yield of the complex ismuch lower than its free ligand. This result is in good agreement with thetheoretical calculations TD-DFT performed on the ligand and the complex,indicating a higher contribution of MLLCT than 1IL states to theelectronic  transitions  that are populated by excitation at 350 nm.Flashphotolyses results agreed, either in aqueous or MeCN solutions, helped toidentify the naterure of the generated excited states. In aqueous solutions the3IL state of Ptr in the Re-complex was detected. However, in MeCNsolutions, flash photolyses experiments showed spectral features of thegenerated transients more consistent with the emitting 3MLCT. Thedeactivation of 3MLCT by O2 leads to the formation of 1O2with a low quantum yield. No formation of 1O2 in D2Owas detected, possibly due to a very low 3IL formation quantumyield. LIOAS spectroscopy confirmed that this complex released to the medium all the absorbedenergy as prompt heat after laser excitation at 355 nm either in H2Oand/or MeCN.Thereduced transient spectrum generated by flash photolysis is in good agreementwith the published spectra of the reduced ligand radical [2]. Pulseradiolysis experiments under oxidizing and/or reducing environments wereperformed in aqueous solutions of the Re complex. By performing an analysis byMCR-ALS, it was possible to identify the contribution of three species. Thefirst intermediate was assigned, by spectral similarity, to the semireducedradical of the free ligand [3,4]. Thisspectrum also agrees with the spectrum found for the reduced transientgenerated 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, thiscompares very well with those published for ReII, leading us topropose oxidation in the metal core as the reaction product of the transientunder oxidizing conditions.  [1]      F. Ragone, G. T. G. T. Ruiz, O. E. O. E.Piro, G. A. G. a. Echeverría, F. M. F. M. Cabrerizo, G. Petroselli, R.Erra-Balsells, K. Hiraoka, F. S. F. S. García Einschlag, E. Wolcan, Eur. J.Inorg. Chem. 2012, 2012, 4801?4810.[2]      C. Chahidi, M. Aubailly, Photochem.Photobiol. 1981, 33, 641?649.[3]      P. Moorthy, E. Hayon, J. Org. Chem 1976,41, 1607?1613.[4]      M. Farahank, P. S. Surdhar, S. Allen, D.A. Armstrong, J. Chem. Soc. Perkin Trans. 1991, 2,1687?1693.