Thermally Activated Delayed Fluorescence Emitters for Deep Blue Organic Light Emitting Diodes: A Review of Recent Advances

Abstract

Organic light-emitting diodes offer attractive perspectives for the next generation display and lighting technologies. The potential is huge and the list of potential applications is almost endless. So far, blue emitters still suffer from noticeably inferior electroluminescence performances in terms of efficiency, lifespan, color quality, and charge injection/transport when compared to that of the other colors. Emitting materials matching the NTSC standard blue of coordinates (0.14, 0.08) are extremely rare and still constitutes the focus of numerous academic and industrial researches. In this context, we review herein the recent developments on highly emissive deep-blue thermally activated delayed fluorescence emitters that constitute the third-generation electroluminescent materials.

Aggregation‐Induced and Polymorphism‐Dependent Thermally Activated Delayed Fluorescence (TADF) Characteristics of an Oligothiophene: Applications in Time‐Dependent Live Cell Multicolour Imaging

“…Thus, the enhanced emission observed for 1 in higher water fractions can be attributed to the formation of fluorescent nanoparticles (FNPs). These results clearly indicate that compound 1 is a good AIEEgen and comparable with the characteristics of AIEEgen reported elsewhere …”

“…Compound 1 was characterizedb yN MR ( 1 H, 13 C) and ESI-mass spectrometric studies (see the SI). The 1 Ha nd 13 CNMR spectral pattern and their relative integrationv alues are consistent with the molecular structure of 1.T he molecular structureo f1 was further confirmed by single-crystal X-ray diffraction analysis. It is noteworthy to mentiont hat synthesis and basic optical properties of structurally similar 2,5-bis(2,2di(thiophen-3-yl)vinyl)thiophene was reported by Ikeda et al in the year 2014.…”

“…However, the large twist angle also affects the transition dipole which in turn controls the important photophysical quantities such as radiative and non‐radiative decay process. Thus, only the lower Δ E ST value would not guarantee the TADF properties, conceivably significant superposition between the HOMO and LUMO of D‐A systems is mandatory to realize efficient TADF process …”

“…The results showed that T 2 state is placed close to the S 1 state. Moreover, the commonality of the orbitals involved in S 0 →S 1 and S 0 → T 1or2 transitions suggest that the ISC and rSIC transitions occurs via these triplet states (ESI, Table ST7) . Further, to establish the role of molecular conformation in TADF characteristics of 1 .…”

“…Thus, only the lower DE ST value would not guarantee the TADF properties, conceivably significant superposition between the HOMO and LUMO of D-A systems is mandatory to realize efficient TADF process. [13] .T herefore, the challenge in developing TADF emitters is design am olecular system with low DE ST value with significant rSIC and retaining S 1 !S 0 radiative decay.V ery recently Ikuta et al elegantly exploitedt he multiple resonance structure of boron and nitrogen centers in polycyclic aromatic compounds and developed new type of pure deep blue TADF emitters. [14] In the presentc ase, the TADF properties of 1 is very intriguing, because, compound 1 is not at ypical D-A system, to get insight into the possible ISC pathways, vertical transitions between S 0 !T n state were calculated.…”