Theoretical Insights into the Photo-Deactivation of Emitting Triplet Excited State of (C^N)Pt(O^O) Complexes: Radiative and Nonradiative Decay Processes

In this study, density functional theory (DFT) and time-dependent DFT were employed to elucidate the photo-deactivation mechanisms of (C^N)­Pt­(O^O) complexes <b>1</b>–<b>4</b> (where C^N = 2-phenylpyridine derivatives, O^O = dipivolylmethanoate). To make thorough understanding of the radiative decay, the singlet–triplet splitting energies Δ<i>E</i>(S_<i>n</i>–T₁) (<i>n</i> = 1, 2, 3, 4, ...), transition dipole moment μ­(S_<i>n</i>) for S₀–S_<i>n</i> transitions and the spin–orbit coupling (SOC) matrix elements ⟨T₁|H_SOC|S_<i>n</i>⟩ were all calculated. Moreover, the spin–orbit coupling between T₁ and S₀ ⟨T₁|H_SOC|S₀⟩ and Huang–Rhys factors were calculated to estimate the temperature-independent nonradiative decay processes. Meanwhile, the thermal deactivation via metal-centered ³MC was described to analyze the temperature-dependent nonradiative decay processes. As a result, the effective SOC interaction between the lowest triplet and singlet excited states successfully rationalize why complexes <b>1</b> and <b>3</b> have higher radiative decay rate constant than that of complex <b>2</b>, while the larger ⟨T₁|H_SOC|S₀⟩ and lower energy barrier for thermal deactivation in <b>3</b> reasonably explains why <b>3</b> has larger nonradiative rate than that of <b>1</b> and <b>2</b>. Consequently, it can be concluded that it is the ⟨T₁|H_SOC|S₀⟩ and thermal population of ³MC that account for the nonemissive behavior of (C^N)­Pt­(O^O) complexes, and controlling π-conjugation is an efficient method for tuning phosphorescence properties of transition-metal complexes

Proportion of the three growth types in different periods.

<p>Proportion of the three growth types in different periods.</p

Typology of urban growth.

<p>The grey area represents the pre-growth urban patches and the dark area represents the newly grown urban patches.</p

Major historical events related to Shenyang.

<p>Major historical events related to Shenyang.</p

Urban area change of Shenyang from 1910 to 2010.

<p>Urban area change of Shenyang from 1910 to 2010.</p

Change in the landscape indices during the period 1910–2010: (a) number of patches (NP), (b)Patch density (PD), (c) landscape shape index (LSI), and (d) aggregation index (AI).

<p>Change in the landscape indices during the period 1910–2010: (a) number of patches (NP), (b)Patch density (PD), (c) landscape shape index (LSI), and (d) aggregation index (AI).</p

Theoretical Studies of Photodeactivation Pathways of NHC–Chelate Pt(II) Compounds with Different Numbers of Triarylboron Units: Radiative and Nonradiative Decay Processes

The radiative and nonradiative decay processes of four platinum­(II) complexes chelated with triarylboron (TAB)-functionalized N-heterocyclic carbenes (NHC) are investigated by using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculation, for probing into the influence of different numbers of TAB on the phosphorescent emission properties. For the radiative decay processes, zero-field splitting energies, radiative rates, and lifetimes are explored, and corresponding factors including transition dipole moments, singlet–triplet splitting energies as well as spin–orbit coupling matrix elements are also analyzed in detail. Additionally, energy-gap law is considered in the temperature-independent nonradiative decay processes; meanwhile, potential energy profiles are obtained to elaborate the temperature-dependent nonradiative decay processes. As a result, radiative rates declined slightly with the increased numbers of TAB. The minimum temperature-independent nonradiative decay may occur in BC-3 due to its smallest structural distortion between S₀ and T₁ states. According to the potential energy profiles of the deactivation pathways, four investigated phosphors have the similar temperature-dependent nonradiative decay processes because of the incredibly analogous energy barriers. We speculate that it does not mean greater phosphorescent emission and higher phosphorescent quantum yield with more TAB units, which would provide extraordinary assistance for further research in potential phosphors of organic light-emitting diodes

Urban spatial expansion of Shenyang from 1910 to 2010.

<p>(Buffer distance from the Shenyang Imperial Palace: 0–15 kilometers step 1kilometer; 15–25 kilometers step 5 kilometers.).</p

Location of the study area.

<p>Location of the study area.</p