Characterization of excited electronic and vibronic states of platinum metal compounds with chelate ligands by highly frequency-resolved and time-resolved spectra

Abstract

The lowest excited electronic states of triplet character and related vibronic properties are discussed in detail on the basis of highly frequency-resolved and time-resolved emission and excitation spectra of per-protonated, per-deuterated, and partially deuterated [Pt(bpy)2] 2+, [Rh(bpy)3] 3+, [Ru(bpy)3] 2+, and [Os(bpy)3] ~+. Emphasis is placed on the use of the enormous amount of information displayed in well-resolved vibrational satellite structures. For comparison, IR data and Raman spectra are also used. In addition, data are given for [Ru(bpz)Pt(3-thpy) 2, Pt(2-thpy)(CO)(Cl), Pt(2-thpy) 2, Pt(qol)2, Pt(qtl)2. Trends and effects are also addressed, which are related to the amount of metal d-orbital mixing. In particular, we discuss the role of traps and sites in the context of high-resolution, site-selective, and line-narrowed spectra of chromophores doped into matrices; the interplay between states of ligand-centered 3rtrr* and ~MLCT character; localization versus delocalization behavior; radiative decay properties; zero-field splittings; spin-lattice relaxations via direct and Orbach mechanisms; Arrhenius behavior after time delay; Franck-Condon activities and Huang-Rhys factors; Franck-Condon versus Herzberg Teller activities and tunability of these activities under high magnetic fields; isotope marking and deuteration effects; aggregate formation of [Ru(bpy)3]2+; and radiationless energy transfer in neat [Ru(bpy)3](PF6) 2. These effects are in part treated in detail, but the aim is to use easy-to-follow descriptions. In particular, it is emphasized throughout this review that chemical tunability opens fascinating possibilities for controlled variation of physical properties.

Photophysical Properties and OLED Applications of Phosphorescent Platinum(II) Schiff Base Complexes

“…The amount of ZFS can be utilized to classify the degree of MLCT perturbation and SOC efficiency in the emitting triplet state. An empirical ordering scheme developed by Yersin et al [15][16][17][18] for organo-transition-metal triplet emitters provides a useful scale for an assessment of the MLCT perturbation in the T 1 state. Furthermore, the ZFS parameters also give an indication concerning the suitability of a compound for application as an emitter in OLEDs, since all efficient triplet emitters hitherto studied exhibit DEA C H T U N G T R E N N U N G (ZFS) values of theT 1 state larger than about 10 cm À1 .…”

“…A high degree of MLCT character has also been calculated for [IrA C H T U N G T R E N N U N G (ppy) 3 ] in the theoretical works of Hay [26] and Nozaki. 2 + , with zero-field splittings of the lowest triplet state being 60, [17,18] 76, [28] and 211 cm À1 , [17,18] respectively. In contrast, complexes such as [PdA C H T U N G T R E N N U N G (thpy) 2 ] (thpy = 2-(2'-thienyl)pyridyl), [16,29] [Pd(q) 2 ] (q= 8-quinolinato), and [Pt(q) 2 ], [30] as well as [RhA C H T U N G T R E N N U N G (bpy) 3 ] 3 + [31] and [PtA C H T U N G T R E N N U N G (bpy) 2 ] 2 + [17,18] , are characterized by ZFS values significantly below 1 cm À1 .…”

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

“…Additionally,i ti sm entioned that below T % 15 K, effects of spin-lattice relaxation (SLR) between the triplet substates might strongly slow down relaxation processes. [31,33,34,88,95,[138][139][140] Consequently,f requently am ulti-exponential decay (from the different T 1 substates to the ground state S 0 )i so bserved at very low temperature.…”

“…[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.…”

“…Let us focus on the temperature dependence of the emission decay time. With temperature increase, the SLR processes become faster (presumably accordingt oaRamanp rocesso f spin-lattice relaxation (SLR) [138,139,161] )r esulting in af ast thermalizationo ft he three T 1 substates. At sufficiently high temperature, for example, above T = 10 or 20 K, an average emission Figure 10.…”