Year-end Sale % OFF 
Abstract
The effective design of dyes optimized for thermally activated delayed fluorescence (TADF) requires the precise control of two tiny energies: the singlet-triplet gap, which has to be maintained within thermal energy, and the strength of spin-orbit coupling. A subtle interplay among low-energy excited states having dominant charge-transfer and local character then governs TADF efficiency, making models for environmental effects both crucial and challenging. The main message of this paper is a warning to the community of chemists, physicists, and material scientists working in the field: the adiabatic approximation implicitly imposed to the treatment of fast environmental degrees of freedom in quantum-classical and continuum solvation models leads to uncontrolled results. Several approximation schemes were proposed to mitigate the issue, but we underline that the adiabatic approximation to fast solvation is inadequate and cannot be improved; rather, it must be abandoned in favor of an antiadiabatic approach.
Highlights
Activated delayed fluorescence (TADF) occurs in fluorescent systems where triplet states sit very close in energy to the emissive singlet state
To demonstrate that the singlet–triplet inversion calculated in corrected linear response (CLR) and external iteration (EI) for some dyes in non-polar solvents is a spurious effect resulting from the adiabatic approximation to fast solvation, we focus on B1 dye and compare adiabatic and AA results
Thermally activated delayed fluorescence (TADF) dyes are delicate to model since the subtle interplay between localized and charge transfer (CT) states makes environmental or matrix effects crucial in the definition of the tiny energies, the singlet–triplet gap, and the spin–orbit coupling, which define the system performance.[8,9,23,36,41–45]
Summary
Activated delayed fluorescence (TADF) occurs in fluorescent systems where triplet states sit very close in energy to the emissive singlet state. The adiabatic approximation must be abandoned in favor of the antiadiabatic (AA) approximation.[19] cases may occur where the timescales of solute and solvent motions are comparable In these special cases, effective solvation models cannot be reliably defined. When dealing with electronic solvation, we are considering fast DoF: the adiabatic approximation must be abandoned since it relies on a molecular Hamiltonian where the charges in the surrounding solvent are considered frozen, while they move faster than the solute DoF. With reference to TADF dyes, we show how current implementations of continuum solvation models do not properly address environmental effects on the singlet–triplet gap, with results that widely depend on the adopted approximation scheme and lead, in some cases, to an inversion of the order of the lowest singlet and triplet states.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
