Promoting Singlet/triplet Exciton Transformation in Organic Optoelectronic Molecules: Role of Excited State Transition Configuration

Abstract

Exciton transformation, a non-radiative process in changing the spin multiplicity of an exciton usually between singlet and triplet forms, has received much attention recently due to its crucial effects in manipulating optoelectronic properties for various applications. However, current understanding of exciton transformation mechanism does not extend far beyond a thermal equilibrium of two states with different multiplicity and it is a significant challenge to probe what exactly control the transformation between the highly active excited states. Here, based on the recent developments of three types of purely organic molecules capable of efficient spin-flipping, we perform ab initio structure/energy optimization and similarity/overlap extent analysis to theoretically explore the critical factors in controlling the transformation process of the excited states. The results suggest that the states having close energy levels and similar exciton characteristics with same transition configurations and high heteroatom participation are prone to facilitating exciton transformation. A basic guideline towards the molecular design of purely organic materials with facile exciton transformation ability is also proposed. Our discovery highlights systematically the critical importance of vertical transition configuration of excited states in promoting the singlet/triplet exciton transformation, making a key step forward in excited state tuning of purely organic optoelectronic materials.

Resonance‐Activated Spin‐Flipping for Efficient Organic Ultralong Room‐Temperature Phosphorescence

“…Notably, the SOC values of these heteroatom‐containing molecules are significantly larger than those of heteroatom‐free organic molecules (≤0.1 cm −1 ) . Based on both small Δ E ST (<±0.37 eV) and high SOC values (>0.3 cm −1 ), the number of facile ISC channels (blue channels) found in DNCzP , DNCzPO , and DNCzPS are 7, 6, and 10, respectively. However, this theoretical revealing is contradictory to the experimental results, which suggest significantly enhanced ISC in resonance molecules of DNCzPO and DNCzPS with much higher k ISC than that of DNCzP in both solution and solid state at both room temperature and 77 K (Table ; Table S2, Supporting Information).…”

“…First, the energy levels of S 1 and T n are no longer constant in resonance molecules, but will vary within a certain range of E RV due to the self‐adaptive resonance variation, leading to remarkably reduced Δ E ST (real‐time Δ E ST ) to facilitate ISC based on the energy‐gap law (Figure d; Figure S18, Supporting Information). Second, the resonance variation with lone‐pair electron redistribution will lead to a large change of n‐orbital participation (Δα n , Δα n = |α n, S1 – α n, Tn |) for efficient S 1 → T n ISC process with enlarged SOC values, according to the El‐Sayed rule (Figure b; Figure S19, Supporting Information). Consequently, the low‐lying triplet excited states excluded by energy gap law can be activated by resonance variation with E RV T1 up to 1.66 eV in DNCzPO ; also, the low SOC values of the S 1 → T n channels can be significantly enlarged due to large Δα n up to 78% during resonance variation.…”

Thermally activated triplet exciton release for highly efficient tri-mode organic afterglow

“…3e and Supplementary Table 4). Abundant of facile ISC and RISC channels with SOC large than 0.3 cm −1 (blue channels) 32 can be found for the facile exciton transformation of DCzB for OURTP. To theoretically understand the trapping and releasing of triplet excitons stabilized by T 1 * , the quantum mechanics/molecular mechanics (QM/MM) method was performed to evaluate the electronic properties of the active QM dimer embedded in the aggregated crystal state, while the surrounding molecules were defined as rigid MM part to model the effect of solid-state environment (Fig.…”

Dinuclear Silver(I) Nitrate Complexes with Bridging Bisphosphinomethanes: Argentophilicity and Luminescence

“…Analysis of the excited states was done with the Multiwfn program [25]. The similarity of the excited states was analyzed by the approach suggested by Chen [26].…”