In this study, we investigate the lasing properties of 4,4'-bis[(N-carbazole)styryl]biphenyl thin films under electrical pumping. The electroluminescent devices incorporate a mixed-order distributed feedback SiO2 grating into an organic light-emitting diode structure and emit blue lasing. The results provide an indication of lasing by direct injection of current into an organic thin film through selection of a high-gain organic semiconductor showing clear separation of the lasing wavelength from significant triplet and polaron absorption and design of a proper feedback structure with low losses at high current densities. This study represents an important advance toward a future organic laser diode technology.

Indication of current-injection lasing from an organic semiconductor

The wavelength-ratiometric techniques gain increasing popularity in fluorescence probing and sensing for providing inner reference to output signal and removing instrumental artefacts, in this way increasing the sensitivity and reliability of assays. Recent developments demonstrate that such approach can allow achieving much more, with the application of broad range of novel molecular and nanoscale fluorophores (luminophores), exploring the whole power of photophysical and photochemical effects and using extended range of assay formats. Simplicity of detection and potentially rich content of output data allows realizing these techniques in different simplified, miniaturized and multiplexing devices. The latter issues are discussed in Pt. II of these series.

https://iopscience.iop.org/article/10.1088/2050-6120/acc714/pdf

Dual emission and its λ-ratiometric detection in analytical fluorimetry. Pt. I. Basic mechanisms of generating the reporter signal

Achieving high-efficiency deep blue emitter with CIEy  10% has been a long-standing challenge for traditional fluorescent materials in organic light-emitting diodes (OLEDs). Here, we report the rational design and synthesis of two new deep blue luminogens: 4-(10-(4′-(9H-carbazol-9-yl)-2,5-dimethyl-[1,1′-biphenyl]-4-yl)anthracen-9-yl)benzonitrile (2M-ph-pCzAnBzt) and 4-(10-(4-(9H-carbazol-9-yl)-2,5-dimethylphenyl)anthracen-9-yl)benzonitrile (2M-pCzAnBzt). In particular, 2M-ph-pCzAnBzt produces saturated deep blue emissions in a non-doped electroluminescent device with an exceptionally high EQE of 10.44% and CIEx,y (0.151, 0.057). The unprecedented electroluminescent efficiency is attributed to the combined effects of higher-order reversed intersystem crossing and triplet-triplet up-conversion, which are supported by analysis of theoretical calculation, triplet sensitization experiments, as well as nanosecond transient absorption spectroscopy. This research offers a new approach to resolve the shortage of high efficiency deep blue fluorescent emitters.

Exceptionally efficient deep blue anthracene-based luminogens: design, synthesis, photophysical, and electroluminescent mechanisms

The photoelectric response of organic field-effect transistors (OFETs) will cause severe photoelectric interference, which hinders the applications of OFETs in the light environment. It is highly challenging to relieve this problem because of the high photosensitivity of most organic semiconductors. Here, we propose an efficient "exciton-polaron quenching" strategy to suppress the photoelectric response and thus construct highly photostable OFETs by utilizing a polymer electrolyte dielectric─poly(acrylic acid) (PAA). This dielectric produces high-density polarons in organic semiconductors under a gate electric field that quench the photogenerated excitons with high efficiency (∼70%). As a result, the OFETs with PAA dielectric exhibit unprecedented photostability against strong light irradiation up to 214 mW/cm2, which far surpasses the reported values and solar irradiance value (∼138 mW/cm2). The strategy shows high universality in OFETs with different OSCs and electrolytes. As a demonstration, the photostable OFET can stably drive an organic light-emitting diode (OLED) under light irradiation. This work presents an efficient exciton modulation strategy in OSC and proves a high potential in practical applications.

Polymer Electrolyte Dielectrics Enable Efficient Exciton-Polaron Quenching in Organic Semiconductors for Photostable Organic Transistors.

Metal/polymer interfaces play an important role in polymeric light emitting diodes (LEDs). In typical organic light-emitting devices, metallic electrodes are used to inject charged carriers into the organic electroluminescent (EL) medium. However, what other effects the metals have on the organic medium is not well known. In this work, we report severe photoluminescence (PL) quenching of organic thin films comprising of one of the most useful materials, namely 1,4-bis(4-(3,5-di-tert-butylstyryl)styryl]benzene (4PV), upon sub-monolayer deposition of At, Ag, and Ca in an ultra high vacuum environment. The severity of the luminescence quenching may grealtly affect the EL device performance. Gap states at the Ca/4PV interface are shown to be responsible for the PL quenching. The oxidation of Ca resulted in the removal of the gap states and the recovery of the quenched PL.

Metal induced photoluminescence quenching of a phenylene vinylene oligomer and its recovery

Luminescent Lanthanide Metal Organic Frameworks (LnMOFs): A Versatile Platform towards Organomolecule Sensing

A “heat set” Zr-Diimide based Fibrous Metallogel: Multiresponsive Sensor, Column-based Dye Separation, and Iodine Sequestration

Luminescence quenching in the presence of polarons is one of the major challenges in organic light emitting devices. In this work, exciton quenching in the presence of polarons is studied using phase sensitive photocurrent measurements on pentacene field effect transistors. The enhancement of conduction in the organic field effect transistors on light illumination is studied using photocurrent spectral response measurements and corresponding optical simulations. The photocurrent is shown to be governed by the polaron mobility and the exciton quenching efficiency, both of which depend on the polaron density in the channel. Two models are proposed on the exciton dynamics in the presence of gate induced polarons in the transistor channel. The first model simulates the steady-state exciton concentration profile in the presence of exciton-polaron interaction. The second one is a three-dimensional steady state exciton-polaron interaction model, which supports the findings from the first model. It is shown that the excitons quench by transferring its energy to polarons, thereby promoting the latter to high energy states in the density of states manifold. The polarons move in the higher energy states with greater microscopic mobility before thermalizing, thereby leading to an enhancement of conduction. It is observed that for the present system, where charge carrier transport is by hopping, all polarons interact with excitons. This implies that for low mobility systems, the interaction is not limited to deep trapped polarons.

Study of exciton-polaron interaction in pentacene field effect transistors using high sensitive photocurrent measurements

Enhancing the efficiency of red TADF OLED by optimizing the guest-host matrix and charge balance engineering

Four new coordination polymers have been synthesized based on a mixed-ligand strategy, viz., [Cu(4-ABPT)(HNIPA)2H2O]·H2O, SSICG-1; [Cu2(4-ABPT)2(HNIPA)4]·H2O, SSICG-2; [Ni(4-ABPT)(NIPA)H2O], SSICG-3; and [Zn2(ATRZ)2(NIPA)], SSICG-4 (4-ABPT = 3,5-di(pyridine-4-yl)-4H-1,2,4-triazol-4-amine, H2NIPA = 5-nitroisophthalic acid, and ATRZ = 3-amino-1,2,4-triazole, SSICG stands for the Solid State and Inorganic Chemistry Group at IIT Patna). The copper compounds are one-dimensional, whereas the nickel and zinc compounds are two-dimensional layer compounds. SSICG-3 possesses 4,4-net topology with a Schläfli symbol 44.62, whereas SSICG-4 exhibits a 3,3-net (fes) topology with a Schläfli symbol 4.82. SSICG-1 and SSICG-3 have active metal sites due to the presence of replaceable coordinated water molecules and exhibits efficient catalytic activity for one-pot CO2 cycloadditions. The conversions of SSICG-1 and SSICG-3 for CO2 cycloaddition are 87 and 95% (turnover numbers (TON) of 174 and 190), respectively. The kinetic studies, substrate scope, recyclability, catalyst amount, and temperature dependence studies of the CO2 cycloaddition reaction are discussed. These structurally diverse coordination polymers could contribute to broadening the scope of mixed-ligand coordination polymers for their applications in heterogeneous catalysis. 

Subhamoy Sahoo

Papers

Luminescent Lanthanide Metal Organic Frameworks (LnMOFs): A Versatile Platform towards Organomolecule Sensing

A “heat set” Zr-Diimide based Fibrous Metallogel: Multiresponsive Sensor, Column-based Dye Separation, and Iodine Sequestration

Study of exciton-polaron interaction in pentacene field effect transistors using high sensitive photocurrent measurements

Enhancing the efficiency of red TADF OLED by optimizing the guest-host matrix and charge balance engineering

Synthesis, Structure, and Heterogeneous Catalysis of a Series of Structurally Diverse Coordination Polymers Based on 5-Nitroisophthalate