Innovative Organic Electroluminescent Materials with a Doublet Ground State: A Theoretical Investigation

Abstract

The displaced and distorted harmonic oscillator model, which has been proven to be appropriate in calculating vibronic spectra, is employed to treat the emission spectrum of title molecules in combination with a thermal vibration correlation function. The calculated results indicate that the main peak of the emission spectrum is visibly impacted by the normal modes with lower frequencies and that the shoulder peak is originated from the middle-frequency modes. On the level of time-dependent density functional theory (TDDFT), the calculated fluorescence lifetimes of TTM-3NCz and TTM-3PCz are 22.1 and 26.0 ns, respectively, which happen to coincide with the observed values of TTM-3NCz (17.2 ns) and TTM-3PCz (21.2 ns). The above data indicate that both the calculated radiative decay rates are reasonable at room temperature. Furthermore, we investigate the influence of the Duschinsky effect on the fluorescence quantum efficiency (FQE). When it is considered, the predicted FQE of the TTM-3NCz molecule is only 0.11%, and the observed value (49% in toluene) deviates significantly. If we ignore the Duschinsky effect, the FQE of TTM-3NCz increases dramatically to 41.8%. For the TTM-3PCz molecule (the FQE is 46% in toluene), the calculated FQE is 0.042% with the Duschinsky effect and increases to 45.2% without the Duschinsky effect. This phenomenon might be related to external factors and the nature of the TDDFT only considering a single configuration. In addition, the fluorescent properties of the fluorinated TTM-3NCz molecules are studied predictably. The obtained results show that the perfluorinated TTM-3NCz shows better luminous performance due to larger oscillator strength. Finally, the dimers, which are composed of both single title molecules, are explored theoretically to determine how they impact the fluorescent property; however, the effect can be nearly eliminated because of the small binding energies.

Computational Protocol To Predict Anti-Kasha Emissions: The Case of Azulene Derivatives

“…Within this approximation, displacements, distortions, and Duschinsky rotation effects (DREs) are included. This formalism has been proven successful for many different molecular materials, including organic molecules and organometallic complexes. − Furthermore, this formalism was recently used by Shi et al to explain anti-Kasha luminescence in certain dyes, although they only computed radiative rates and they omitted the calculations of IC rates . Certainly, the calculation of anti-Kasha scenarios poses significant additional challenges.…”

Efficient light-emitting diodes from organic radicals with doublet emission

“…On the most electronegative halogen variant, synthesis of a fully fluorinated version of TTM in TTFM has not been reported. Theoretical studies have suggested that replacement of the chlorines in TTM-3NCz with fluorine could cause emission wavelength to drop from 700 nm to 610 nm 69 , however this is still far from the 400-500 nm required for emitting in the blue.…”

Luminescent Radicals

“…This section introduces luminescent polychlorinated TArM radicals, the most-studied group of luminescent radicals to date (Chart and Table ). The following discussion focuses on the TArM radicals that have been synthesized and isolated, although several computational studies have predicted various intriguing polychlorinated TArM radicals. − The discussion covers the basic luminescence properties of the polychlorinated TArM radicals, the current understanding of these radicals based on theoretical aspects, and major scientific advancements related to their unique luminescence properties. Figure summarizes representative or first well-established examples highlighting the development of luminescent polychlorinated TArM radicals.…”