Near-infrared (NIR) light-emitting materials show excellent potential applications in the fields of military technology, bioimaging, optical communication, organic light-emitting diodes (OLEDs),
etc.
...Recently, thermally activated delayed fluorescence (TADF) emitters have made historic developments in the field of OLEDs. These metal-free materials are more attractive because of efficient reverse intersystem crossing processes which result in promising high efficiencies in OLEDs. However, the development of NIR TADF emitters has progressed at a relatively slower pace which could be ascribed to the difficult promotion of external quantum efficiencies. Thus, increasing attention has been paid to NIR TADF emitters. In this review, the recent progress of NIR TADF emitters has been summarized along with their molecular design strategies and photophysical properties, as well as electroluminescence performance data of their OLEDs, respectively.
This review presents the recent progress of NIR TADF emitters along with their molecular design strategies and photophysical properties, as well as the electroluminescence performance data of the emitters and their OLEDs.
Full text
Available for:
IJS, KILJ, NUK, UL, UM, UPUK
Chemical modification of phenothiazine‐benzophenone derivatives tunes the emission behavior from triplet states by selecting the geometry of the intramolecular charge transfer (ICT) state. A ...fundamental principle of planar ICT (PICT) and twisted ICT (TICT) is demonstrated to obtain selectively either room temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF), respectively. Time‐resolved spectroscopy and time‐dependent density functional theory (TD‐DFT) investigations on polymorphic single crystals demonstrate the roles of PICT and TICT states in the underlying photophysics. This has resulted in a RTP molecule OPM, where the triplet states contribute with 89 % of the luminescence, and an isomeric TADF molecule OMP, where the triplet states contribute with 95 % of the luminescence.
Rapid and efficient utilization of triplet states to generate room temperature phosphorescence (RTP) or highly efficient thermally activated delayed fluorescence (TADF) is achieved by structural modification to give a planar or twisted intramolecular charge transfer (PICT or TICT) geometry, respectively.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Although numerous thermally activated delayed fluorescence (TADF) organic light‐emitting diodes (OLEDs) have been demonstrated, efficient blue or even sky‐blue TADF‐based nondoped solution‐processed ...devices are still very rare. Herein, through‐space charge transfer (TSCT) and through‐bond charge transfer (TBCT) effects are skillfully incorporated, as well as the multi‐(donor/acceptor) characteristic, into one molecule. The former allows this material to show small singlet–triplet energy splitting (ΔEST) and a high transition dipole moment. The latter, on the one hand, further lights up multichannel reverse intersystem crossing (RISC) to increase triplet exciton utilization via degenerating molecular orbitals. On the other hand, the nature of the molecular twisted structure effectively suppresses intermolecular packing to obtain high photoluminescence quantum yield (PLQY) in neat flims. Consequently, using this design strategy, T‐CNDF‐T‐tCz containing three donor and three acceptor units, successfully realizes a small ΔEST (≈0.03 eV) and a high PLQY (≈0.76) at the same time; hence the nondoped solution‐processed sky‐blue TADF‐OLED displays record‐breaking efficiency among the solution process‐based nondoped sky‐blue OLEDs, with high brightness over 5200 cd m−2 and external quantum efficiency up to 21.0%.
A novel multi‐(donor/acceptor) thermally activated delayed fluorescence (TADF) molecule with through‐space/‐bond charge transfer is developed. Its nondoped solution‐processed sky‐blue organic light‐emitting diode (OLED) displays high performance with an external quantum efficiency (EQEmax) up to 21.0%, which represents the record‐breaking efficiency among the solution process‐based nondoped sky‐blue OLEDs.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Self-monitoring materials have promising applications in structural health monitoring. However, developing organic afterglow materials for self-monitoring is a highly intriguing yet challenging task. ...Herein, we design two organic molecules with a twisted donor-acceptor-acceptor' configuration and achieve dual-emissive afterglow with tunable lifetimes (86.1-287.7 ms) by doping into various matrices. Based on a photosensitive resin, a series of complex structures are prepared using 3D printing technology. They exhibit tunable afterglow lifetime and Young's Modulus by manipulating the photocuring time and humidity level. With sufficient photocuring or in dry conditions, a long-lived bright green afterglow without apparent deformation under external loading is realized. We demonstrate that the mechanical properties of complex 3D printing structures can be well monitored by controlling the photocuring time and humidity, and quantitively manifested by afterglow lifetimes. This work casts opportunities for constructing flexible 3D printing devices that can achieve sensing and real-time mechanical detection.
Dual luminescence, i.e. intense, simultaneous, room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) is observed in a series of donor–acceptor–donor (D–A–D) ...molecules. This dual luminescence is stronger in the “angular” isomers, compared to their “linear” regioisomers, which is consistent with an enhanced intersystem crossing (ISC) in the former. Herein, we demonstrate that the small energy gap between the triplet levels, T 1 –T n , below the lowest singlet state, S 1 , in the “angular” regioisomers, enhances the coupling between S 1 and T 1 states and favors ISC and reverse ISC (rISC). This is consistent with a spin–vibronic mechanism. In the absence of this “triplet ladder”, due to the larger energy difference between T 1 and T n in the “linear” regioisomers, the ISC and rISC are not efficient. Remarkably, the enhancement of the ISC rate in the “angular” regioisomers is accompanied by an increase of the rate of internal conversion (IC). These results highlight the contributions of higher triplet excited states and molecular vibronic coupling to the harvest of triplet states in organic compounds, and cast the TADF and RTP mechanisms into a common conceptual framework.
A series of novel donor–acceptor–donor (D–A–D) compounds featuring dibenzothiophene ( DBT ) and phenothiazine ( PTZ ) units are presented. A different degree of steric hindrance between the donor and ...acceptor fragments is achieved by the systematic changes of donor substituents (methyl, iso-propyl, tert -butyl groups). This leads to the tuning of photophysical properties by conformational control. The unsubstituted DPTZ–DBT molecule exists in both equatorial and axial forms in the ground state, due to the ability of PTZ to form H-extra and H-intra folded conformers that allow formation of parallel quasi-axial (ax) and perpendicular quasi-equatorial (eq) conformers, respectively. However, the equatorial conformer prevails in the excited state. This leads to strong room temperature phosphorescence (RTP) in the green region with high phosphorescence quantum yield (60 ± 8%). Under the influence of bulky substituents, the alkyl- DPTZ–DBT derivatives change molecular conformation, preventing formation of the excited charge transfer state. Hence, blue, but much weaker, phosphorescence is observed. The less bulky methyl substituent on the donor results in dual RTP (blue and green), apparently violating Kasha's rule imposed by the modulation of the barriers between excited states. The experimental results are supported by DFT calculations in the ground and excited state. Control of conformation with substituents is an effective strategy for tuning the excited state properties of D–A–D molecules for RTP emission.
In this work, a new series of 2-hydroxybenzophenone (BPOH) derivatives, BPOH-TPA, BPOH-PhCz, and BPOH-SF substituting with different electron-donating groups are designed and synthesized. ...Dual-emission spectra are observed in solutions indicating their excited-state intramolecular proton transfer (ESIPT) character. In solid states, all compounds exhibit a broad emission spectrum when excited at low excitation energy, deriving from the enol-type form stabilized by intramolecular hydrogen bonds. Compound BPOH-TPA shows a clear excitation wavelength dependence. However, such behavior is absent in BPOH-PhCz and BPOH-SF, as the rigid and weaker donor moieties may restrict this process. Furthermore, by increasing the excitation energy, dual emission with a high-energy band ranging from 550 to 582 nm and a low-energy band ranging from 625 to 638 nm is obtained in all three molecules. The photophysical studies and single-crystal analyses are performed to further illustrate the excitation-dependent emission. Higher excitation energies can promote more excitons to keto forms via ESIPT, giving a stronger redshifted emission. BPOH-TPA with a stronger donor strength exhibits an obvious color change gradually from yellow to orange-red with the increasing excitation power from 1 to 15 mW/cm
2
. This study provides a novel example of ESIPT materials with tunable emission colors.
Photoresponsive materials have been widely used in sensing, bioimaging, molecular switches, information storage, and encryption nowadays. Although a large amount of photoresponsive materials have ...been reported, the construction of these smart materials into precisely prescribed complex 3D geometries is rarely studied. Here we designed a novel photoresponsive material methyl methacrylate containing triphenylethylene (TrPEF
2
-MA) that can be directly used for digital light processing (DLP) 3D printing. Based on TrPEF
2
-MA, a series of photoresponsive 3D structures with reversible color switching under ultraviolet/visible light irradiations were fabricated. These complex photoresponsive 3D structures show high resolutions (50
μ
m), excellent repeatability (25 cycles without fatigue), and tunable saturate color degrees. Multicomponent DLP 3D printing processes were also carried out to demonstrate their great properties in information hiding and information-carrying properties. This design strategy for constructing photoresponsive 3D structures is attractive in the area of adaptive camouflage, information hiding, information storage, and flexible electronics.
Phenazine derivative molecules were studied using steady state and time resolved fluorescence techniques and demonstrated to lead to strong formation of aggregated species, identified as dimers by ...time dependent density functional theory calculations. Blended films in a matrix of Zeonex®, produced at different concentrations, showed different contributions of dimer and monomer emissions in a prompt time frame, e.g. less than 50 ns. In contrast, the phosphorescence (e.g. emission from the triplet state) shows no significant effect on dimer formation, although strong dependence of the phosphorescence intensity on concentration is observed, leading to phosphorescence being quenched at higher concentration.
Organic mechanoluminescent (ML) materials possessing photophysical properties that are sensitive to multiple external stimuli have shown great potential in many fields, including optic and sensing. ...Particularly, the photoswitchable ML property for these materials is fundamental to their applications but remains a formidable challenge. Herein, photoswitchable ML is successfully realized by endowing reversible photochromic properties to an ML molecule, namely 2‐(1,2,2‐triphenylvinyl) fluoropyridine (o‐TPF). o‐TPF shows both high‐contrast photochromism with a distinct color change from white to purplish red, as well as bright blue ML (λML = 453 nm). The ML property can be repeatedly switched between ON and OFF states under alternate UV and visible light irradiation. Impressively, the photoswitchable ML is of high stability and repeatability. The ML can be reversibly switched on and off by conducting alternate UV and visible light irradiation in cycles under ambient conditions. Experimental results and theoretical calculations reveal that the change of dipole moment of o‐TPF during the photochromic process is responsible for the photoswitchable ML. These results outline a fundamental strategy to achieve for the control of organic ML and pave the way to the development of expanded smart luminescent materials and their applications.
Manipulation of mechanoluminescence in organic molecules has tremendous application potential in many fields. Here an example is successfully developed to realize photoswitchable mechanoluminescence byendowing reversible photochromic properties to organic mechanoluminescent molecule. It provides a suggestive molecular designing strategy to achieve novel smart luminescent materials toward widespread applications in material science fields.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
PDF
