Thermally Tunable Dual Emission of the d⁸–d⁸ 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 (5d z 2 –6p z ) excitations, i.e., the singlet state S1 (of 1A2u symmetry in D4h) and the lowest triplet T1, which splits into spin–orbit substates A1u(3A2u) and Eu(3A2u). 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.

TADF Material Design: Photophysical Background and Case Studies Focusing on CuIand AgIComplexes

“…Thus, the emission of the powder material can display molecular properties. Accordingly, concentration quenching does not occur and the decay behavior does not show any distinctive feature (such as shortening of decay times) with concentration increase …”

“…[31,96] Moreover,i ft he splitting of the T 1 state into substates of af ew cm À1 (a few 0.1 meV) and the corresponding photophysical properties should be addressed, extension of the temperature range to about T = 1.3 K( and application of as lightly modified Equation (1) is required. [58,70,88,89,97,139,146] In Sections 3, 4, and6 ,w ew ill present case studies. In these we will show how to develop ad eeper understanding of representative compounds.…”

“…Accordingly, concentration quenching does not occur and the decay behavior does not show any distinctive feature (such as shortening of decay times) with concentration increase. [30,31,58,95] 3. Case Study:T ADF of aCu I Complexw ith…”

“…[7,[20][21][22][23][24][25][26][27][28] These scientific investigations led to am uch deeper understanding of photophysical principles and of the compound's properties resultingi nt he development of an enormousn umber of new materials in part with drastically improved properties for OLED applications. [4,9, Improvements were also stimulated in the fields of related functional materials based on metal complexes for sensing of oxygen or temperature [53][54][55][56][57][58][59] or for photocatalysis. [60][61][62][63][64][65][66] For luminescent materials to be applied in OLEDs, it is essential that all excitons generatedi nt he emission layer are harvesteda nd converted into photons.…”

The interplay between fluorescence and phosphorescence with luminescent gold(i) and gold(iii) complexes bearing heterocyclic arylacetylide ligands

“…There are also cases where comparable k ISC and k r of S 1 → S 0 leads to the observation of dual fluorescence–phosphorescence under steady-state condition, e.g. , [Pt(L)(acac)] and [Ir(L)(acac)] (L = 2-(oligothienyl)pyridine); 26 [Os(L)(CO) 3 X] (L = 8-quinolinolate 27 or isoquinoline-triazole), 28 and [Bu 4 N] 4 [Pt 2 (μ-P 2 O 5 (BF 2 ) 2 ) 4 ], 29 etc. …”