Recent progress in imidazole based efficient near ultraviolet/blue hybridized local charge transfer (HLCT) characteristic fluorophores for organic light-emitting diodes

Abstract

Organic light-emitting diodes (OLEDs) are the most successful invention of organic electronics in today’s market and have received persistent attention from industrial and scientific communities. OLEDs have rapidly developed into...

Efficient blue fluorescent OLEDs based on a D–π–A emitter with the hybridized localized and charge-transfer state

“…Considering the energy diagram and the NTO distributions of TAZ-An-TPA , we speculated that the most likely mechanism of high η exciton of TAZ-An-TPA is HLCT. 20,47–49 The energy diagram (Fig. S7, ESI†) shows that TPA-An-TPA has a large T 2 –T 1 energy gap (1.1797 eV) and small T 2 –S 1 (0.0035 eV), which reduces the internal conversion efficiency from T 2 to T 1 and favors the RISC from T 2 to S 1 .…”

Recent Advances in Triplet–Triplet Annihilation-Based Materials and Their Applications in Electroluminescence

“…For some types of fluorescent emitters, the excitons can be directly formed via the high-lying excited states of the emitters during device operation. , In 2014, the first hybridized local and charge transfer (HLCT) process for these fluorescent emitters was proposed by Ma and co-workers, and they observed the efficient and fast RISC from high-lying triplet state T m ( m ≥2) to singlet state S n ( n ≥1) of these fluorescent emitters at room temperature (Figure ), which is called the “hot exciton” process . Hot exciton materials usually show a small T m –S n energy splitting and a large T m –T 1 energy gap.…”

“…The small T m –S n energy gap will increase the RISC rate from T m to S n , and the large T m –T 1 energy gap can suppress the IC from T m to T 1 . Theoretically, all of the high-energy triplet excitons can be converted to singlet excitons, resulting in 100% exciton utilization efficiency in hot exciton materials. − …”

“…34−38 For some types of fluorescent emitters, the excitons can be directly formed via the high-lying excited states of the emitters during device operation. 60,61 In 2014, the first hybridized local Efficient and stable blue organic lightemitting devices represent one of the most important components in future solid-state lighting and full color displays. and charge transfer (HLCT) process for these fluorescent emitters was proposed by Ma and co-workers, and they observed the efficient and fast RISC from high-lying triplet state T m (m≥2) to singlet state S n (n≥1) of these fluorescent emitters at room temperature (Figure 3), which is called the "hot exciton" process.…”

Progresses and Perspectives of Near-Infrared Emission Materials with “Heavy Metal-Free” Organic Compounds for Electroluminescence

“…When this electron is excited to the lowest singly unoccupied molecular orbital (SUMO), the SOMO is empty, and transition of the excited electron back to the SOMO is totally spin-allowed. (3) The hybridized local and charge-transfer state (HLCT) material [ 51 , 52 , 53 ] with the “hot excitons” which could undergo a reverse intersystem crossing process (RISC) through the high-lying channel, and then the excitons could go through a radiative transition to the low-lying locally excited (LE) state to produce a radiative exciton ratio that break through the limit of 25% of spin statistics. (4) The thermally activated delayed fluorescence (TADF) [ 54 , 55 , 56 ] materials with small singlet-triplet energy gap (ΔE ST ) make use of efficient reverse intersystem crossing (RISC) from the lowest triplet state (T 1 ) to the lowest singlet state (S 1 ) so that the theoretical internal quantum efficiency can reach 100%.…”