title: Thermally Tunable Dual Emission of the d(8)-d(8) Dimer [Pt2(μ-P2O5(BF2)2)4](4).
abstract: High-resolution fluorescence, phosphorescence, as well as related excitation spectra, and, in particular, the emission decay behavior of solid [Bu4N]4[Pt2(μ-P2O5(BF2)2)4], abbreviated Pt(pop-BF2), have been investigated over a wide temperature range, 1.3-310 K. We focus on the lowest excited states that result from dσ*pσ (5dz(2)-6pz) excitations, i.e., the singlet state S1 (of (1)A2u symmetry in D4h) and the lowest triplet T1, which splits into spin-orbit substates A1u((3)A2u) and Eu((3)A2u). After optical excitation, an unusually slow intersystem crossing (ISC) is observed. As a consequence, the compound shows efficient dual emission, consisting of blue fluorescence and green phosphorescence with an overall emission quantum yield of ∼ 100% over the investigated temperature range. Our investigation sheds light on this extraordinary dual emission behavior, which is unique for a heavy-atom transition metal compound. Direct ISC processes in Pt(pop-BF2) are largely forbidden due to spin-, symmetry-, and Franck-Condon overlap-restrictions and, therefore, the ISC time is as long as 29 ns for T < 100 K. With temperature increase, two different thermally activated pathways, albeit still relatively slow, are promoted by spin-vibronic and vibronic mechanisms, respectively. Thus, distinct temperature dependence of the ISC processes results and, as a consequence, also of the fluorescence/phosphorescence intensity ratio. The phosphorescence lifetime also is temperature-dependent, reflecting the relative population of the triplet T1 substates Eu and A1u. The highly resolved phosphorescence shows a ∼ 220 cm(-1) red shift below 10 K, attributable to zero-field splitting of 40 cm(-1) plus a promoting vibration of 180 cm(-1).
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Regensburg , Universitätstrasse 31, D-93040 Regensburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hofbeck
authors.affiliation: Beckman Institute, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Yan Choi
authors.initials: YC
authors.lastname: Lam
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic , Dolejškova 3, CZ-182 23 Prague, Czech Republic.
authors.forename: Martin
authors.initials: M
authors.lastname: Kalbáč
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic , Dolejškova 3, CZ-182 23 Prague, Czech Republic.
authors.forename: Stanislav
authors.initials: S
authors.lastname: Záliš
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic , Dolejškova 3, CZ-182 23 Prague, Czech Republic.|School of Biological and Chemical Sciences, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom.
authors.forename: Antonín
authors.initials: A
authors.lastname: Vlček
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Regensburg , Universitätstrasse 31, D-93040 Regensburg, Germany.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Yersin