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Chromophores undergoing excited‐state intramolecular proton transfer (ESIPT) feature a distinct four‐level photocycle and significant Stokes shift, which make them ideal for achieving population inversion upon photoexcitation, a fundamental prerequisite for lasing, by mitigating the concerns of self‐absorption owing to spectral overlap. This study focuses on functionalizing the hydroxyphenyl‐benzothiazole (HBT) ESIPT laser dye through the introduction of fluorene and phenyl‐carbazole moieties at the para‐position to the hydroxyl group, to demonstrate amplified spontaneous emission (ASE) activities. The synthesized HBT derivatives not only exhibit high thermal and photostability, but also high photoluminescence quantum yields, exceeding 40%, which is noteworthy for ESIPT materials emitting in the yellow–orange to red color ranges. Computational analyses show that these new HBT materials possess substantially lower ESIPT energy barriers, compared to their parent HBT, facilitating their efficient ESIPT processes. Moreover, these derivatives demonstrate a high radiative rate of 1.47 × 108 s−1. Thin films of a fluorene‐substituted HBT (HBT‐pFl) show a low solid‐state amplified spontaneous emission threshold value of 3.8 µJ cm−2 at 582 nm, representing the lowest reported solid‐state ASE threshold for laser dyes in the orange emission region (575–600 nm) to date. [ABSTRACT FROM AUTHOR]

External quantum efficiency (EQE) roll‐off under high current injection has been one of the major limiting factors toward the development of organic semiconductor laser diodes (OSLDs). While significant progress in this regard has been made on organic semiconductors (OSCs) emitting in the blue–green region of the visible spectrum, OSCs with longer wavelength emission (>600 nm) have fallen behind in both material development and the advancement in device architectures suitable for the realization of OSLDs. Therefore, to make simultaneous incremental advancements, a host–guest system comprising of a high performing poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT) polymer and an efficient small molecule laser dye, dithiophenyl diketopyrrolopyrrole (DT‐DPP), is used. This combination provides an extremely low amplified spontaneous emission threshold of 4.2 µJ cm−2 at an emission wavelength of 620 nm. The solution‐processed organic light‐emitting diodes (OLEDs) fabricated using this system exhibit a high external quantum efficiency (EQE) of 2.6% with low efficiency roll‐off and high current injection up to 90 A cm−2 to yield ultrahigh luminance of over 1.5 million cd m−2. [ABSTRACT FROM AUTHOR]

Over the years, achieving efficient electroluminescence (EL) while simultaneously having low light amplification thresholds under optical excitation has been the key to progression toward the long‐thought objective of electrically pumped organic lasers. While significant progress in this regard has been made for organic semiconductors emitting in the blue–green region of the visible spectrum, organic laser dyes with low‐energy emission (>600 nm) still suffer from high amplified spontaneous emission (ASE) thresholds and low external quantum efficiencies (EQEs) in devices. Herein, low ASE thresholds and efficient EL are reported from a solution‐processable organic laser dye dithiophenyl diketopyrrolopyrrole (DT‐DPP). The ASE threshold of 4 µJ cm−2 at the wavelength of 620 nm is obtained while making constructive use of triplet excitons by doping DT‐DPP in a green‐emitting host matrix, which exhibits thermally activated delayed fluorescence (TADF). The organic light‐emitting diode fabricated from this system gives a high EQE of 7.9% due to the efficient utilization of triplet excitons. Transient EL studies further show that a high reverse intersystem crossing rate is crucial in achieving lasing under electrical pumping from such TADF‐assisted fluorescent systems. [ABSTRACT FROM AUTHOR]

High mechanical flexibility and wavelength tunability of organic semiconductor materials have propelled the development of organic semiconductor lasers (OSLs) as a complementary technology to current inorganic lasers. While excellent progress has been made across multiple aspects of OSLs, demonstration of long‐pulse operation [quasi‐continuous wave (qCW) or continuous wave (CW)] lasing has presented significant challenges due to the detrimental accumulation of triplets under long‐pulse photoexcitation and substantial quenching of singlet excitons, arising from singlet‐triplet annihilation (STA). In particular, qCW or CW lasing from solution‐processed OSL materials has not been reported, and thus remains a long‐thought objective in optoelectronic research. Using a novel bis(N‐carbazolylstyryl)‐9,9‐dihexylfluorene (BSFCz), the first solution‐processable organic laser dye demonstrating lasing oscillation in the long‐pulse photoexcitation regime (up to 10 ms pulse width) with a low threshold (420 W cm−2), which in part can be attributed to its negligible spectral overlap between triplet excited‐state absorption and laser emission, is herein reported. Temporal emission profiles below and above the lasing threshold also demonstrate that STA has a negligible effect on emission. These combined observations show BSFCz incur low losses due to triplet excited‐states, leading to extremely small changes in lasing thresholds when moving from pulsed to qCW (>1 ms) excitation. [ABSTRACT FROM AUTHOR]

Organic semiconductor dyes have attracted high interest as laser gain media owing to their judicious features of solution processability, lightweight, high mechanical flexibility, high wavelength‐tunability, and low‐cost manufacture. In this work, fluorene‐carbazolylstyryl hybrids are reported, SFCz and BSTFCz, as new solution processable organic semiconductor laser dyes to show high molar extinction coefficients (up to 1.98 × 105 dm3 mol−1 cm−1), high photoluminescence quantum yields (up to 81 ± 4%), high radiative decay constants (up to 1.24 × 109 s−1), and low film amplified spontaneous emission thresholds (down to 0.70 µJ cm−2). By using mixed‐order distributed feedback laser structures, extremely low lasing threshold of 0.5 µJ cm−2 is achieved. To elucidate their electroluminescent properties, simple solution‐processed organic light‐emitting diodes based on the new materials are fabricated to show good external quantum efficiencies (2%) and high brightness (≈2800 cd m−2). The results indicate the ease in material synthesis and fabrication enabling solution‐processed low‐threshold lasing toward future injection laser. [ABSTRACT FROM AUTHOR]

Triplet excitons have been identified as the major obstacle to the realisation of organic laser diodes, as accumulation of triplet excitons leads to significant losses under continuous wave (CW) operation and/or electrical excitation. Here, we report the design and synthesis of a solid-state organic triplet quencher, as well as in-depth studies of its dispersion into a solution processable bis-stilbene-based laser dye. By blending the laser dye with 20 wt% of the quencher, negligible effects on the ASE thresholds, but a complete suppression of singlet–triplet annihilation (STA) and a 20-fold increase in excited-state photostability of the laser dye under CW excitation, were achieved. We used small-area OLEDs (0.2 mm2) to demonstrate efficient STA suppression by the quencher in the nanosecond range, supported by simulations to provide insights into the observed STA quenching under electrical excitation. The results demonstrate excellent triplet quenching ability under both optical and electrical excitations in the nanosecond range, coupled with excellent solution processability. Though reducing non-emissive triplet excited-states using quenchers effectively improves organic semiconductor laser diode (OSLD) performance, existing quenchers are not suitable for devices. Here, the authors designed a solid-state triplet quencher for OSLD under optical and electrical excitation. [ABSTRACT FROM AUTHOR]

While noteworthy progress has been made on organic solid‐state lasers with low amplified spontaneous emission (ASE) thresholds and high optical gains in blue and green colors, the same advancement has not been achieved for red laser dyes. This is mainly due to their low photoluminescence quantum yields (PLQYs) because of "energy bandgap law." Here, a new family of solution‐processable organic semiconductor laser dyes based on a bay‐annulated indigo derivative (Cibalackrot) with deep‐red emission is reported. They exhibit excellent PLQYs and low ASE thresholds (9.6 µJ cm−2) with deep‐red emission when blended in a mixed host of 1,3‐bis(N‐carbazolyl)benzene (mCP) and 2‐hydroxyphenylbenzothiazole (HBT). In contrast to a single blend in mCP, the co‐blend films are found to significantly enhance the photostability by retaining 90% of initial ASE intensity even after continuous pumping with over 9000 pulses at a pump input energy twice that of the ASE threshold, which can be attributed to efficient cascade energy transfer from mCP to HBT and then to the Cibalackrot chromophore. Low lasing threshold of 6 µJ cm−2 is further achieved at 641 nm by using distributed feedback gratings. Transient absorption spectroscopy measurements indicate that the dye has extremely low yield of triplet excited‐state under optical excitation. The results show Cibalackrot derivatives to be a promising new family of organic deep‐red laser dyes. [ABSTRACT FROM AUTHOR]