QM and ONIOM studies on thermally activated delayed fluorescence of copper(i) complexes in gas phase, solution, and crystal

Abstract

Herein, we have employed B3LYP and TD-B3LYP methods with the QM/MM approach to study the thermally activated delayed fluorescence (TADF) phenomenon of two Cu(i) complexes bearing 5-(2-pyridyl)-tetrazolate (PyrTet) and phosphine (POP) ligands in the gas phase, solution, and crystal form. On the basis of spectroscopic properties, ground- and excited-state geometric and electronic structures, and related radiative and nonradiative rates, we have found that (1) the S1 and T1 excited states have clear metal-to-ligand charge transfer character from the Cu(i) atom to the PyrTet group; (2) the S1 and T1 states have a very small energy gap ΔES1-T1, less than 0.18 eV, which makes the forward and reverse intersystem crossing ISC and rISC processes between the S1 and T1 states very efficient; and (3) the low-frequency vibrational modes related to the torsional motion of the POP and PyrTet groups are found to have significant Huang-Rhys factors and are responsible for the efficient ISC and rISC rates. However, the corresponding Huang-Rhys factors are remarkably suppressed in the crystal compared with those in the gas phase and in solution due to the rigidity of the crystal surroundings; as a result, the ISC and rISC rates are accordingly reduced slightly in the crystal. This comparison also demonstrates that the surrounding effects are very important for modulating the photophysical properties of the Cu(i) complexes. Finally, our work gives helpful insights into the TADF mechanism of the Cu(i) compounds, which could assist in rationally designing TADF materials with excellent performance.

QM/MM studies on luminescence mechanism of dinuclear copper iodide complexes with thermally activated delayed fluorescence

“…31 This strategy has been demonstrated to work well in previous works. [32][33][34] The minima are optimized by the DFT (S 0 ) and TD-DFT (S 1 and T 1 ) methods with the hybrid exchange-correlation functional (PBE1PBE). [35][36][37] In all these calculations, the Stuttgart relativistic pseudopotential and its accompanying basis set (SDD, ECP60MWB) are applied for the Cu and I atoms; the 6-31G* [6-31+G*] basis set is used for C, H and N [P] atoms.…”

TADF: Enabling luminescent copper(i) coordination compounds for light-emitting electrochemical cells

“…2). 118 Related studies which address the effects of both intramolecular and intermolecular interactions on photophysical properties, have been carried out This journal is © The Royal Society of Chemistry 20xx…”

“…0.18 eV, 1500 cm -1 ) separation in the tetrazole-containing [Cu(POP) (15)], and theoretical studies indicate that introducing methyl substituents into the backbone of POP to give Me 2 POP (Scheme 15) has little effect on the T 1 -S 1 energy gap. 118 There appear to be no experimental investigations of the effects on the properties of [Cu(POP)(N^N)] + -type complexes of modifying the POP ligand, and there are only limited studies on complexes incorporating modified xantphos ligands. In 2019, we reported the use of the 123 Thus, the modifications of xantphos, either with bulky peripheral groups, or with P-substituents more sterically demanding that phenyl, do not appear to enhance PL or EL properties, and these latter investiagtions tend to suggest that, with xantphos at least, the choice of N^N ligand is the dominant factor.…”

“…2 ). 118 Related studies which address the effects of both intramolecular and intermolecular interactions on photophysical properties, have been carried out on the cationic TADF emitters [Cu(POP)(16)] + and [Cu(POP)(17)] + . 119 These complexes exhibit both aggregation induced emission (AIE) and TADF.…”

“…0.18 eV, 1500 cm −1 ) separation in the tetrazole-containing [Cu(POP)(15)], and theoretical studies indicate that introducing methyl substituents into the backbone of POP to give Me 2 POP ( Scheme 15 ) has little effect on the T 1 –S 1 energy gap. 118 There appear to be no experimental investigations of the effects on the properties of [Cu(POP)(N^N)] + -type complexes of modifying the POP ligand, and there are only limited studies on complexes incorporating modified xantphos ligands. In 2019, we reported the use of the t Bu 2 xantphos ligand ( Scheme 15 ).…”