Hybridized Local and Charge-Transfer Excited-State Fluorophores through the Regulation of the Donor–Acceptor Torsional Angle for Highly Efficient Organic Light-Emitting Diodes

Abstract

Hybridized local and charge-transfer (HLCT) excited-state fluorophores, which enable full exciton utilization through a reverse intersystem crossing from high-lying triplet states to singlet state, have attracted increasing attention toward organic light-emitting diodes (OLEDs) application. Herein, we report three D-π-A-π-D-type isomers o-2CzBT, m-2CzBT, and p-2CzBT by adjusting the donor (D) units from ortho-, meta-, to para-substituted positions with the acceptor (A) core unit, respectively. The HLCT properties of the three compounds are evidently confirmed by theoretical calculations, solvatochromic behaviors, and transient decay lifetimes analyses. As the substituted position changes from the ortho-, meta-, and para-positions, the reduced steric hindrance brings about decreased torsional angle between D and A moieties, resulting in increased oscillator strength. Accordingly, the para-substituted p-2CzBT is endowed with a more locally excited component that accounts for faster radiative decay, leading to a higher fluorescent efficiency than that of o-2CzBT and m-2CzBT. As expected, p-2CzBT enables its nondoped and doped OLEDs with higher external quantum efficiencies (EQEs) of 12.3% and 15.0%, respectively, which are among the state-of-the-art efficiencies of HLCT-based OLEDs. Moreover, o-2CzBT and m-2CzBT are also utilized as host materials for high-performance OLEDs, thus extending the application of HLCT materials.

Aggregation Turns BODIPY Fluorophores into Photosensitizers: Reversibly Switching Intersystem Crossing On and Off for Smart Photodynamic Therapy

“…Organic fluorophores are widely used in many areas such as fluorescent probes [1][2][3][4][5][6] , bioimaging [7][8][9][10][11] and organic light emitting diodes [12][13][14] . Normally, exciting a fluorophore in dilute solution generates a lowest singlet excited state (S 1 ), which rapidly relaxes back to the ground state (S 0 ) through emitting fluorescence.…”

Rational Design of Chrysene‐Based Hybridized Local and Charge‐Transfer Molecules as Efficient Non‐Doped Deep‐Blue Emitters for Simple‐Structured Electroluminescent Devices

“… [13a] In addition, the push‐pull or donor‐acceptor feature formed between TPA (as a donor) and electron‐rich chrysene (as an acceptor) moieties would also enable the mixture of locally excited and charge transfer excited state, giving rise to the hybridized local excited and charge transfer (HLCT) excited state fluorescence molecules [14] . Since the HLCT state can achieve theoretical maximum exciton utilization efficiency (EUE max ) of 100% because of the RISC process occurring at high‐lying energy levels, [15] the efficient bifunctional deep‐blue emitters would be developed. As anticipated, the molecules emit a deep‐blue color with a high Φ PL and HLCT property and are effectively employed as non‐doped emitters in simple structured OLEDs (ITO/PEDOT : PSS : NF/emitter/TPBi/LiF : Al).…”

Twisted Phenanthro[9,10‐d]imidazole Derivatives as Non‐doped Emitters for Efficient Electroluminescent Devices with Ultra‐Deep Blue Emission and High Exciton Utilization Efficiency

“…While their PL spectra gradually red‐shifted with increasing the solvent polarity due to the existence of charge transfer (CT) component. As a comparison, SAF‐PI displays a stronger solvatochromic effect with a redshift of 42 nm from xylene to acetonitrile, indicating more CT components [16] . The plots of the stokes shift versus the orientation polarizability ( f ) of the solvents revealed the apparent change of the dipole moment between the ground and the excited states seeing as two‐section line fitting as illustrated in Figure 2d (Table S2, ESI).…”