Wavelength-Turnable Organic Microring Laser Arrays from Thermally Activated Delayed Fluorescent Emitters

Abstract

Organic solid-state lasers (OSSLs) have been paid great attention due to their ease-of-fabrication, low cost and tailor-made molecular tunability. Optical gain materials of OSSLs are currently focused on fluorescent materials, which can bring only 25% exciton utilization for future current-injection OSSLs due to spin statics under electrical excitation. While thermally active delayed fluorescent (TADF) materials can obtain a theoretical 100% internal quantum efficiency by harvesting triplet excitons. However, OSSLs based on TADF materials remain largely unexplored yet. Here, we report the first TADFbased OSSL from whispering-gallery mode microring resonator arrays fabricated by a confined solution-growth method. The newly designed TADF emitter of carbozyl borondifluoride curcuminoid derivative, namely, CAZ-A, when doped into a host matrix of 4,4′-bis(N-carbazolyl)-1,10-biphenyl (CBP), reaches the highest gain-coefficient of 640 cm −1 at 4 wt %. These MRs with well-controlled sizes and uniform geometries constitute a high quality (cavity quality factor Q ∼ 1300) built-in WGM resonators and exhibit outstanding multimode laser behaviors. By varying TADF molecule doping concentration, the laser wavelength can be continuously tuned in the red spectral range from 650 to 725 nm. As CBP is usually used as the host material for active layers in OLEDs, we believe that CAZ-A/CBP doping material is good candidate for future electrically driven OSSLs.

Computational screen-out strategy for electrically pumped organic laser materials

“…Instead, these materials can serve as triplet harvesters to improve the performance of the organic laser dye 18 . With that being said, a few studies have reported lasing activities from newly designed TADF molecules [19][20][21][22] . In these studies, the S 1 states of the corresponding TADF molecules show effective overlaps (instead of being fully orthogonal) between natural transition orbitals based on the computational results, which potentially enlarge f em , and thus will not violate the statement we have drawn here.…”

Regulation of Thermally Activated Delayed Fluorescence to Room‐Temperature Phosphorescent Emission Channels by Controlling the Excited‐States Dynamics via J‐ and H‐Aggregation

“…Note that such al arge energy gap between S 1 and T 1 makes the RISC directly from T 1 to S 1 almost impossible.Asshown below by theoretical calculation results,T ADF of bCBF 2 in dilute DCM might be enabled by an ultra-fast RISC between high-lying T n and S 1 states. [12] Density functional theory (DFT) and time-dependent DFT (TD-DFT) at B3LYP/6-31G(d) level combined with polarization continuum model (PCM) were used for theoretical calculation to explore the mechanism of TADF characteristics of bCBF 2 molecule.T he ground-state structure exhibit ad ihedral angle (q)b etween the difluoroboron naphthalene plane and the nitrobenzene plane about q = 36.98 8 (Table S1). And the calculated vertical energy is 3.09 eV,consistent with the absorption maximum at 412 nm.…”

Toward Electrically Pumped Organic Lasers: A Review and Outlook on Material Developments and Resonator Architectures

“…[34d] Huang et al fabricated a microring WGM resonator with a TADF emitter, 4,6-bis((E)-9-ethyl-3-vinyl-9H-carbazole)-5-(ethoxycarbonyl)-2,2difluoro-2H-1,3,2-dioxaborinin-1-ium-2-uide, namely, CAZ-A/ CPB, which exhibited a clear laser peak at 683 nm with a threshold value of 3.96 μJ cm À2 and Q factor of %1300. [80] In a very recent work, [34c] Zhou et al reported direct evidence about the influence of RISC on lasing from a TADF emitter, namely, 2,3,5,6-tetrakis (carbazol-9-yl)-1,4-dicyanobenzene 4CzTPN doped in polystyrene (PS) microspheres (see in Figure 6). They claimed that the observed increase (decrease) in lasing intensity (SE lifetime) with temperature was caused by an accelerated depletion of singlet excitons promoted by the upconverted triplets.…”