Computational design of efficient near-infrared TADF emitters with hot-exciton characteristics

Abstract

Developing near-infrared (NIR) TADF emitters is challenging due to the inherent energy gap law. In this work, we designed a set of twelve donor-acceptor1-acceptor2 (D-A1-A2) type NIR pure organic emitter...

Overcoming the Limitation of Spin Statistics in Organic Light Emitting Diodes (OLEDs): Hot Exciton Mechanism and Its Characterization

“…For designing OLED materials with computational means, the ability of calculating various transition rate coefficients can play an important role for both radiative and nonradiative decays, as the calculation can directly lead to property prediction such as the luminescence efficiency. Indeed, numerous studies have been reported for such calculations [119,[132][133][134][135], and similar studies may prove their utility, especially toward testing the hypotheses. Provided that there is still some room for practical improvements for the related formalisms as mentioned in Section 3.5, we expect that future methodology developments and computational studies based on them will provide valuable insights for designing hot exciton materials.…”

“…Several papers reported predictions on the hRISC rates with the help of the thermal vibration correlation function (TVCF) formalism [117]. However, the IC rates were either not really compared to [102,118,119] or actually shown to be much faster than the hRISC rate [120]. Nevertheless, solid experimental evidence exists to show that the hot exciton materials bear preferable properties that cannot be explained through TADF and/or TTA mechanisms.…”

Combined DFT and QM/MM Modeling on Multifunctional TADF Sensitizers and Hot-Exciton Emitters via Carborane Triads for Blue Hyperfluorescent OLEDs

“…Hot exciton emitters harness dark triplet excitons from higher-energy triplet states to radiative singlet states, effectively utilizing these triplet excitons through a fast nanosecond-scale RISC process. 56 Kasha's rule in photochemistry states that significant photon emission primarily originates from the lowest excited state of a given multiplicity. Certain materials exhibit distinctive electronic structures and energy level arrangements, hindering internal conversion from higher excited states (Hot-Excitons) to S 1 or T 1 and enabling direct photochemical processes, contrary to Kasha's rule.…”

“…Consequently, there is a critical need to address the efficient utilization of dark triplet excitons. Hot exciton emitters harness dark triplet excitons from higher-energy triplet states to radiative singlet states, effectively utilizing these triplet excitons through a fast nanosecond-scale RISC process . Kasha’s rule in photochemistry states that significant photon emission primarily originates from the lowest excited state of a given multiplicity.…”

“…Hence, hot exciton emitters need to meet specific criteria. (i) To prevent the rapid internal conversion process, it is essential to maintain a significant energy gap between T 2 and T 1 states, (ii) The T 2 state and higher-lying triplet states (T 3 , T 4 ...) are degenerate with the S 1 state to enable the up-conversion of high-lying triplet hot excitons that are upconverted from T 2 and T n states to the S 1 state and, finally, TADF emission originates from the S 1 state into the ground state as delayed fluorescence (iii) High magnitudes of SOC, ISC, and RISC rates are required between the T 2 and S 1 states. , To achieve this, we have selected molecules 31 to 42 , which incorporate P-BODIPY acceptor units to represent hot exciton emitters. The singlet energies decrease systematically from 2.39 to 1.89 eV in ortho, from 2.59 to 2.07 eV in meta, and from 2.63 to 2.11 eV in para-carborane-based molecules, corresponding to an increase in the potential of the donor units (Tables S13 and S14).…”