Zusammenfassung
High-resolution fluorescence, phosphorescence, as well as related excitation spectra, and, in particular, the emission decay behavior of solid [Bu4N](4)[Pt-2(mu-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 d sigma*p sigma (Sd(z)(2)-6p(z)) excitations, i.e., the singlet state S-1 ...
Zusammenfassung
High-resolution fluorescence, phosphorescence, as well as related excitation spectra, and, in particular, the emission decay behavior of solid [Bu4N](4)[Pt-2(mu-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 d sigma*p sigma (Sd(z)(2)-6p(z)) excitations, i.e., the singlet state S-1 (of (1)A(2u) symmetry in D-4h) and the lowest triplet T-1, which splits into spin-orbit substates A(1u)((3)A(2u)) and E-u((3)A(2u)). 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 similar to 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 T-1 substates E-u and A(1u). The highly resolved phosphorescence shows a similar to 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).
Altmetric