Ultrafast electronic and vibrational relaxations in mixed-ligand dithione-dithiolato Ni, Pd, and Pt complexes

0437613 - ÚFCH JH 2015 RIV GB eng J - Článek v odborném periodiku
Frei, F. - Rondi, A. - Espa, D. - Mercuri, M. L. - Pilia, L. - Serpe, A. - Odeh, A. - van Mourik, F. - Chergui, M. - Feurer, T. - Deplano, P. - Vlček, Antonín - Cannizzo, A.
Ultrafast electronic and vibrational relaxations in mixed-ligand dithione-dithiolato Ni, Pd, and Pt complexes.
Dalton Transactions. Roč. 43, č. 47 (2014), s. 17666-17676. ISSN 1477-9226. E-ISSN 1477-9234
Grant CEP: GA MŠMT LD14129
Institucionální podpora: RVO:61388955
Klíčová slova: 2ND-ORDER NLO PROPERTIES * SENSITIZED SOLAR-CELLS * FEMTOSECOND FLUORESCENCE
Kód oboru RIV: CF - Fyzikální chemie a teoretická chemie
Impakt faktor: 4.197, rok: 2014

Ultrafast excited-state dynamics of planar Pt, Pd, and Ni dithione-dithiolato complexes were investigated by transient absorption spectroscopy on the femtosecond-picosecond timescale. All studied complexes show a common photobehaviour, although individual kinetics parameters and quantum yields vary with the metal, the dithione ligand and, namely the solvent (DMF, MeCN). Laser pulse irradiation at 800 nm populates the lowest singlet excited state of a dithiolato -> dithione charge transfer character, (LL)-L-1'CT. The optically excited state undergoes a solvation-driven sub-picosecond electronic relaxation that enhances the dithione/dithiolato charge separation. The (LL)-L-1'CT state decays with a 1.9-4.5 ps lifetime by two simultaneous pathways: intersystem crossing (ISC) to the lowest triplet state (LL)-L-3'CT and non-radiative decay to the ground state. ISC occurs on a similar to 6 ps timescale, virtually independent of the metal, whereas the rate of the non-radiative decay to the ground state decreases on going from Ni (2 ps) to Pd (3 ps) and Pt (similar to 10 ps). (LL)-L-3'CT is initially formed as a vibrationally excited state. Its equilibration (cooling) takes place on a picosecond timescale and is accompanied by a competitive decay to the ground state. Equilibrated (LL)-L-3'CT is populated with a quantum yield of less than 50%, depending on the metal: Pt > Pd > Ni. (LL)-L-3'CT is long-lived for Pt and Pd (> 500 ps) and short-lived for Ni (similar to 15 ps). Some of the investigated complexes also exhibit spectral changes due to vibrational cooling of the singlet (2-3 ps, depending on the solvent). Rotational diffusion occurs with lifetimes in the 120-200 ps range. Changing the dithione (Bz(2)pipdt/(i)Pr(2)pipdt) as well as dithiolate/diselenolate (dmit/dsit) ligands has only small effects on the photobehavior...
Trvalý link: http://hdl.handle.net/11104/0241132