Close Energy Levels Research Articles

Toward Efficient Modeling of Nonradiative Decay in Extended INVEST: Overcoming Computational Challenges in Quantum Dynamics Simulations.

In recent years, an increasing number of fully organic molecules capable of thermally activated delayed fluorescence (TADF) have been reported, often with very small or even inverted singlet-triplet (INVEST) energy gaps. These molecules typically exhibit complex photophysics due to the close energy levels of multiple singlet and triplet states, which create various transition pathways toward emission. A predictive model for the rates of these transitions is thus essential for assessing the suitability of new materials for light-emitting devices. Quantum Dynamics (QD) calculations are ideal for this purpose, as they include quantum effects, without the limitations of first-order perturbative approaches, also allowing taking into account more than two electronic states at once. However, the huge computational demands of QD methodologies, especially for large molecules, currently limit their use as a standard tool. To address this problem, we here employ a strategy that allows us to include almost the whole set of the vibrational coordinates by selecting the key elements of the Hilbert space that significantly impact dynamics, thereby hugely reducing the computational burden. Application of this protocol to two relatively large INVEST molecules reveals that internal conversion in these systems is very fast, making indirect emissive pathways a possible channel for the population of the S1 state. More importantly, this study demonstrates that the dynamics can be accurately described even with a significantly reduced vibrational space, thus allowing quantum dynamics calculations that yield accurate transition rates in a few minutes of computational time.

Pressure-induced hydrogen bonding modulating Fermi resonance between fundamental modes in xylitol molecule

Xylitol, as a typical polyol, has a broad range of application prospects. However, the molecular states of xylitol under different environments are rarely reported until now. In this work, the state changes of xylitol molecules under high pressure were analyzed by Raman spectra. A Fermi resonance phenomenon in the fundamental mode of xylitol at 2945 (±0.06) cm−1 and 2955 (±0.41) cm−1 was observed at 0.99 GPa. The Fermi doublets possess the same symmetry and close energy levels, which had not been changed by pressures. However, the high pressure shortened the atomic distances and applied the extra disturbance, providing the necessary conditions for energy transfer. Besides, the Fermi doublets decoupling happened at 4 GPa due to the breaking of hydrogen bonding. This work provides an important reference for studying molecular states and weak interactions of polyols under high pressures.

Theoretical Design of Strengthened Nanotwinned γ*-Boron.

The distinctive electron deficiency and unusual multicenter bonding situations of boron give rise to fascinating chemical complexity and imaginative structural polymorphism. Herein, we employ an independently developed method to construct the new twinned γ*-boron based on the well-known hardest elemental boron, γ-B28. Notably, the newly propounded γ*-boron phases exhibit considerably close energy levels with γ-B28 under ambient conditions. The simulated X-ray diffraction patterns of stable twinned structure present excellent agreement with experimental data. First-principles calculations reveal a 7.5% increase in the ideal Vickers shear strength of γ*-boron compared to γ-B28, attributed to diverse bond responses within the twinned slabs. The evaluated hardness of nanotwinned γ*-B reaches 59 GPa in consideration of the size hardening effect. Our research presents an efficient strategy for constructing new polymorphs of boron with improved mechanical properties and expands the knowledge about twinning structures of boron.

Mechanism of Tunable Band Gap of Halide Cubic Perovskite CsPbBr3−xIx

Perovskites are organic-inorganic compounds with a crystal structure that revolutionize many optoelectronic applications, especially solar cells. The CsPbBr3−xIx, a perovskite, has garnered significant attention due to its tunable band gap and excellent photovoltaic properties. In this theoretical study, the structural, electronic, and optical properties of CsPbBr3−xIx are investigated through density functional theory calculations. The calculations reveal that the substitution of Br with I leads to a significant reduction in the band gap of CsPbBr3−xIx, resulting in improved light absorption properties. The obtained data show that the coexistence of Br and I ions in the structure creates an energy level similar to the shallow energy levels caused by doping at the R symmetry point in the band structure.

Regulating the proximity effect of heterocycle-containing AIEgens

Proximity effect, which refers to the low-lying (n,π*) and (π,π*) states with close energy levels, usually plays a negative role in the luminescent behaviors of heterocyclic luminogens. However, no systematic study attempts to reveal and manipulate proximity effect on luminescent properties. Here, we report a series of methylquinoxaline derivatives with different electron-donating groups, which show different photophysical properties and aggregation-induced emission behaviors. Experimental results and theoretical calculation reveal the gradually changed energy levels and different coupling effects of the closely related (n,π*) and (π,π*) states, which intrinsically regulate proximity effect and aggregation-induced emission behaviors of these luminogens. With the intrinsic nature of heterocycle-containing compounds, they are utilized for sensors and information encryption with dynamic responses to acid/base stimuli. This work reveals both positive and negative impacts of proximity effect in heterocyclic aggregation-induced emission systems and provides a perspective to develop functional and responsive luminogens with aggregation-induced emission properties.

Economical and Environmentally Friendly Organic hydrazone Derivatives Characterized by a Heteroaromatic Core as Potential Hole Transporting Materials in Perovskite Solar Cells

AbstractA series of organic electron‐rich π‐bridged symmetric hydrazones, composed of two donor moieties connected through a thiophene‐ or a pyrrole‐based π‐spacer, has been synthesized as a suitable alternative to 2,2’,7,7’‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9’‐spirobifluorene (Spiro‐OMeTAD), considered the benchmark hole transporting material (HTM) in perovskite solar cells (PSCs). The cheap synthetic protocol is suitable for potential large‐scale production. All the compounds were characterized, showing good energy levels alignments with the perovskite and very close energy levels to the Spiro‐OMeTAD. Furthermore, computational analysis confirmed the electrochemical trend observed. The costs of synthesis were estimated, as well as the produced waste to synthesise the final HTMs, underlining the low impact of these compounds on the environment with the respect to Spiro‐OMeTAD. Overall, the relevant electrochemical properties and the low cost of the synthetic approaches allow these compounds to be a greener and easy‐to‐synthesize alternative to the Spiro‐OMeTAD for industrial development of PSCs.

Pseudo-Qutrit Formed by Two Interacting Identical Spins (s = 1/2) in a Variable External Magnetic Field.

An analytical solution is obtained for the problem of two interacting, identical but separated spin 1/2 particles in a time-dependent external magnetic field, in a general case. The solution involves isolating the pseudo-qutrit subsystem from a two-qubit system. It is shown that the quantum dynamics of a pseudo-qutrit system with a magnetic dipole-dipole interaction can be described clearly and accurately in an adiabatic representation, using a time-dependent basis set. The transition probabilities between the energy levels for an adiabatically varying magnetic field, which follows the Landau-Majorana-Stuckelberg-Zener (LMSZ) model within a short time interval, are illustrated in the appropriate graphs. It is shown that for close energy levels and entangled states, the transition probabilities are not small and strongly depend on the time. These results provide insight into the degree of entanglement of two spins (qubits) over time. Furthermore, the results are applicable to more complex systems with a time-dependent Hamiltonian.

Tantalum-Zirconium Co-Doped Metal-Organic Frameworks Sequentially Sensitize Radio-Radiodynamic-Immunotherapy for Metastatic Osteosarcoma.

Due to radiation resistance and the immunosuppressive microenvironment of metastatic osteosarcoma, novel radiosensitizers that can sensitize radiotherapy (RT) and antitumor immunity synchronously urgentlyneeded. Here, theauthors developed a nanoscale metal-organic framework (MOF, named TZM) by co-doping high-atomic elements Ta and Zr as metal nodes and porphyrinic molecules (tetrakis(4-carboxyphenyl)porphyrin (TCPP)) as a photosensitizing ligand. Given the 3D arrays of ultra-small heavy metals, porous TZM serves as an efficient attenuator absorbing X-ray energy and sensitizing hydroxyl radical generation for RT. Ta-Zr co-doping narrowed the highest occupied molecular orbital-lowest unoccupied molecular orbital(HOMO-LUMO) energy gap and exhibited close energy levels between the singlet and triplet photoexcited states, facilitating TZM transfer energy to the photosensitizer TCPP to sensitize singlet oxygen (1 O2 ) generation for radiodynamic therapy (RDT). The sensitized RT-RDT effects of TZM elicit a robust antitumor immune response by inducing immunogenic cell death, promoting dendritic cell maturation, and upregulating programmed cell death protein 1 (PD-L1) expression via the cGAS-STING pathway. Furthermore, a combination of TZM, X-ray, and anti-PD-L1 treatments amplify antitumor immunotherapy and efficiently arrest osteosarcoma growth and metastasis. These results indicate that TZM is a promising radiosensitizer for the synergistic RT and immunotherapy of metastatic osteosarcoma.

Activating Energy Transfer Tunnels by Tuning Local Electronegativity of Conjugated Polymeric Backbone for High‐Efficiency OLEDs with Low Efficiency Roll‐Off

AbstractThermally activated delayed fluorescence (TADF) conjugated polymers are attractive for display and illumination applications owing to their excellent device performance and convenient device fabrication. However, conjugated polymers frequently encounter insufficient energy transfer from hosts to TADF units, lowering device performance. Herein, a strategy for improving light‐emitting performances through adjusting the local electronegativity of the polymeric backbones by inserting electron‐withdrawing atoms and activating energy transmission channels is proposed. Meanwhile, strongly electronegative atoms also affect the charge‐transfer natures (CT) of TADF polymers and minimize the energy difference between the lowest singlet and triplet states, leading to a rapid reverse intersystem crossing process through the vibronic coupling between 1CT and 3CT with extremely close energy levels. The produced TADF polymer, pBP‐PXZ, can achieve an external quantum efficiency (EQE) of 23.11%, exhibiting no roll‐off when the luminance is less than 200 cd m−2 whereas only a 3% EQE decrease at 500 cd m−2. The EQE can even maintain above 19% under 1000 cd m−2, which is the highest efficiency among TADF polymer‐based organic light‐emitting diodes (OLEDs) under high luminance. The study provides a new perspective for designing high‐performance OLEDs materials.

An Element‐Substituted Cyclobutadiene Exhibiting High‐Energy Blue Phosphorescence

1,3,2,4-Diazadiboretidine, an isoelectronic heteroanalogue of cyclobutadiene, is an interesting chemical species in terms of comparison with the carbon system, whereas its properties have never been investigated experimentally. According to Baird's rule, Hückel antiaromatic cyclobutadiene acquires aromaticity in the lowest triplet state. Here we report experimental and theoretical studies on the ground- and excited-state antiaromaticity/aromaticity as well as the photophysical properties of an isolable 1,3,2,4-diazadiboretidine derivative. The crystal structure of the diazadiboretidine derivative revealed that the B2 N2 ring adopts a planar rhombic geometry in the ground state. Yet, theoretical calculations showed that the B2 N2 ring turns to a square geometry with a nonaromatic character in the lowest triplet state. Notably, the diazadiboretidine derivative has the lowest singlet and triplet states lying at close energy levels and displays blue phosphorescence.

An Element‐Substituted Cyclobutadiene Exhibiting High‐Energy Blue Phosphorescence

Abstract1,3,2,4‐Diazadiboretidine, an isoelectronic heteroanalogue of cyclobutadiene, is an interesting chemical species in terms of comparison with the carbon system, whereas its properties have never been investigated experimentally. According to Baird's rule, Hückel antiaromatic cyclobutadiene acquires aromaticity in the lowest triplet state. Here we report experimental and theoretical studies on the ground‐ and excited‐state antiaromaticity/aromaticity as well as the photophysical properties of an isolable 1,3,2,4‐diazadiboretidine derivative. The crystal structure of the diazadiboretidine derivative revealed that the B2N2 ring adopts a planar rhombic geometry in the ground state. Yet, theoretical calculations showed that the B2N2 ring turns to a square geometry with a nonaromatic character in the lowest triplet state. Notably, the diazadiboretidine derivative has the lowest singlet and triplet states lying at close energy levels and displays blue phosphorescence.

Non‐fullerene all small molecule OBHJSCs with profound device characteristics

AbstractIn this work, we have reported two donor materials ONAF and SNAF that complement the widely used non‐fullerene acceptor ITIC, with the aim to develop non‐fullerene all small molecule organic bulk heterojunction solar cells (NF‐ASM‐OBHJSCs). Two small molecule donors A‐D‐D'‐D‐A architecture, namely ONAF and SNAF are synthesized and explored their ability to act as donor material along with the ITIC acceptor. Benzodithiophene (BDT) is used as central donor unit (dialkoxy‐BDT for ONAF and Dialkylthiophene‐BDT for SNAF) along with novel naphthodithiophene (NDT) terminal donor to improve light harvesting and charge conducting ability of the donor materials. N‐Butylrhodanine is employed as terminal acceptor to enhance the intramolecular charge transfer (ICT) and to place energy level of the donor materials. Both the small molecule donor materials have good thermal stability, broad and intense absorption displayed in the UV‐vis region with energy levels suitable for ITIC acceptor. NF‐ASM‐OBHJSCs are fabricated by using all small molecules (ONAF & SNAF) as donors and ITIC as acceptor. OBHJSCs based on SNAF displayed superior photovoltaic properties with power conversion efficiency (PCE) as 9.94 % (Jsc = 15.93 mA cm‐2, Voc = 0.96 V and FF = 0.65) compared to ONAF based devices with PCE as 7.48 % (Jsc = 14.93 mA cm‐2, Voc = 0.82 V and FF = 0.61). The substantial high PCE of SANF is attributed to the broad absorption, relatively well‐matched HOMO‐LUMO energy levels between SNAF – ITIC acceptor, better film morphology for efficient charge transport and exciton dissociation at donor/acceptor (D‐A) junction. The observed PCE is one of the best reported for the NDT‐BDT‐based all small molecule non‐fullerene OBHJSCs. Moreover, simplicity in the device fabrication procedures and low energy loss associated are added advantages with the SNAF based devices. We predict that the HOMO‐LUMO levels (CV) of D/A falling in this category, as in Figure S7, with further close energy levels will have implications on the efficiency of OBHJSCs.

Efficient Nonfullerene Organic Solar Cells with Small Driving Forces for Both Hole and Electron Transfer.

State-of-the-art organic solar cells (OSCs) typically suffer from large voltage loss (Vloss ) compared to their inorganic and perovskite counterparts. There are some successful attempts to reduce the Vloss by decreasing the energy offsets between the donor and acceptor materials, and the OSC community has demonstrated efficient systems with either small highest occupied molecular orbital (HOMO) offset or negligible lowest unoccupied molecular orbital (LUMO) offset between donors and acceptors. However, efficient OSCs based on a donor/acceptor system with both small HOMO and LUMO offsets have not been demonstrated simultaneously. In this work, an efficient nonfullerene OSC is reported based on a donor polymer named PffBT2T-TT and a small-molecular acceptor (O-IDTBR), which have identical bandgaps and close energy levels. The Fourier-transform photocurrent spectroscopy external quantum efficiency (FTPS-EQE) spectrum of the blend overlaps with those of neat PffBT2T-TT and O-IDTBR, indicating the small driving forces for both hole and electron transfer. Meanwhile, the OSCs exhibit a high electroluminescence quantum efficiency (EQEEL ) of ≈1 × 10-4 , which leads to a significantly minimized nonradiative Vloss of 0.24 V. Despite the small driving forces and a low Vloss , a maximum EQE of 67% and a high power conversion efficiency of 10.4% can still be achieved.

Interface traps contribution on transport mechanisms under illumination in metal–oxide–semiconductor structures based on silicon nanocrystals

The transport phenomena in metal–oxide–semiconductor (MOS) structures having silicon nanocrystals (Si-NCs) inside the dielectric layer have been investigated, in dark condition and under visible illumination. At first, using deep-level transient spectroscopy (DLTS), we find the presence of series electron traps having very close energy levels (comprised between 0.28 and 0.45 eV) for ours devices (with/without Si-NCs). And a single peak appears at low temperature only for MOS with Si-NCs related to Si-NCs DLTS response. In dark condition, the conduction mechanism is dominated by the thermionic fast emission/capture of charge carriers from the highly doped polysilicon layer to Si-substrate through interface trap states for MOS without Si-NCs. The tunneling of charge carriers from highly poly-Si to Si substrate trough the trapping/detrapping mechanism in the Si-NCs, at low temperature, contributed to the conduction mechanism for MOS with Si-NCs. The light effect on transport mechanisms has been investigated using current–voltage (I–V), and high frequency capacitance–voltage (C–V) methods. We have been marked the photoactive trap effect in inversion zone at room temperature in I–V characteristics, which confirm the contribution of photo-generated charge on the transport mechanisms from highly poly-Si to Si substrate trough the photo-trapping/detrapping mechanism in the Si-NCs and interfaces traps levels. These results have been confirmed by an increasing about 10 pF in capacity’s values for the C–V characteristics of MOS with Si-NCs, in the inversion region for inverse high voltage applied under photoexcitation at low temperature. These results are helpful to understand the principle of charge transport in dark condition and under illumination, of MOS structures having Si-NCs in the SiOx= 1.5 oxide matrix.

Interface traps effect on the charge transport mechanisms in metal oxide semiconductor structures based on silicon nanocrystals

The transport phenomena in Metal-Oxide-Semiconductor (MOS) structures having silicon nanocrystals (Si-NCs) inside the dielectric layer has been investigated by high frequency Capacitance-Voltage (C-V) method and the Deep-Level Transient Spectroscopy (DLTS). For the reference samples without Si-NCs, we observe a slow electron trap for a large temperature range, which is probably a response of a series electron traps having a very close energy levels. A clear series of electron traps are evidenced in DLTS spectrum for MOS samples with Si-NCs. Their activation energies are comprised between 0.28eV and 0.45eV. Moreover, we observe in this DLTS spectrum, a single peak that appears at low temperature which we attributed to Si-NCs response. In MOS structure without Si-NCs, the conduction mechanism is dominated by the thermionic fast emission/capture of charge carriers from the highly doped polysilicon layer to Si-substrate through interface trap-states. However, at low temperature, the tunneling of charge carriers from highly Poly-Si to Si-substrate trough the trapping/detrapping mechanism in the Si-NCs contributed to the conduction mechanism for MOS with Si-NCs. These results are helpful to understand the principle of charge transport of MOS structures having a Si-NCs in the SiOx=1.5 oxide matrix.

Promoting Singlet/triplet Exciton Transformation in Organic Optoelectronic Molecules: Role of Excited State Transition Configuration

Exciton transformation, a non-radiative process in changing the spin multiplicity of an exciton usually between singlet and triplet forms, has received much attention recently due to its crucial effects in manipulating optoelectronic properties for various applications. However, current understanding of exciton transformation mechanism does not extend far beyond a thermal equilibrium of two states with different multiplicity and it is a significant challenge to probe what exactly control the transformation between the highly active excited states. Here, based on the recent developments of three types of purely organic molecules capable of efficient spin-flipping, we perform ab initio structure/energy optimization and similarity/overlap extent analysis to theoretically explore the critical factors in controlling the transformation process of the excited states. The results suggest that the states having close energy levels and similar exciton characteristics with same transition configurations and high heteroatom participation are prone to facilitating exciton transformation. A basic guideline towards the molecular design of purely organic materials with facile exciton transformation ability is also proposed. Our discovery highlights systematically the critical importance of vertical transition configuration of excited states in promoting the singlet/triplet exciton transformation, making a key step forward in excited state tuning of purely organic optoelectronic materials.

Conservative Difference Scheme for Maxwell Equations Describing a Nonstationary Nonlinear Response of Matter in a Semi-Classical Approximation

A conservative difference scheme is constructed for the system of equations that describe, in the semi-classical approximation, resonance and nonresonance interaction of an electromagnetic pulse with matter. The conservativity of the scheme is proved. A cascade mechanism for the excitation of high energy levels in the medium under the impact of a narrow-spectrum electromagnetic pulse is demonstrated. In the cascade mechanism, if the spectrum does not contain a pulse of sufficiently high frequencies to trigger direct transitions from the ground state to high excited states, the molecules of the medium may still reach the high states through a series of successive transitions between nearer lying energy levels. This may lead to the appearance in the transmitted pulse of higher frequencies than those observed in the incident pulse. For a medium whose length is comparable with the spatial extent of the pulse, distortion of the transmitted pulse spectrum is observed. The absolute phase of the small-period pulse substantially affects the transformation of the pulse spectrum during the transmission through the matter. If the matter contains several close energy levels, the corresponding transition rates will depend on the absolute phase of the field. We demonstrate and explain the generation of the third harmonic during the interaction of the electromagnetic pulse with the medium due to the nonstationary and nonlinear character of the response.

A new generation of organic light-emitting materials and devices

Organic light-emitting diodes (OLEDs) have been a research focus for almost 30 years because of their great potential applications in flat-panel displays, solid-state lighting, and wearable electronics. The recombination of holes and electrons within the devices under electrical excitation typically generates 25% singlet excitons and 75% triplet excitons. However, only 25% singlet excitons can be utilized to emit light, and the other 75% triplet excitons are generally wasted through non-radiative transition to give a maximum internal quantum efficiency of about 25% for the first generation fluorescent OLEDs. To improve the internal quantum efficiency, phosphorescent materials have been utilized to exploit the non-radiative triplet state by introducing noble heavy metal atoms like iridium (Ir) and platinum (Pt) to increase spin-orbit interactions. Overall electroluminescence (EL) internal quantum efficiency has been successfully improved to 100% since both singlet and triplet excitons could be harvested due to their radiative triplet excitons and efficient intersystem crossing (ISC) from the singlet excited state to the triplet excited state. Nevertheless, noble metals are indispensable for those phosphorescent materials, which are expensive and nonrenewable. In the past few years, metal-free thermally activated delayed fluorescence (TADF) emitters that can also realize 100% exciton utilization through efficient reverse intersystem crossing (RISC) of triplet excitons are regarded as promising materials for next-generation OLEDs. Besides, the intersystem crossing of excitons between higher energy Tm and Sn with close energy levels may also happen in hybridized local and charge-transfer (HLCT) excited state, where the local excited (LE) state contributes to a high efficiency fluorescence radiative decay, while the charge transfer (CT) state ensures the generation of singlet excitons in high yield through the reverse intersystem crossing from high-lying CT-based triplet excited state back to the CT-based singlet excited state. 75% Non-luminescent triplet excitons can theoretically be transferred to singlet ones via reverse intersystem crossing to give a comparable internal quantum efficiency to that of the phosphorescent devices. In addition, an organic open-shell molecule with one unpaired electron in the highest singly occupied molecular orbital (SOMO) could also be used as an emitter to circumvent the transition problem of triplet. Intermixing of electron-donating and electron-accepting molecules as an emitting layer could also break the fluorescence internal quantum efficiency limit of 25% by using the high reverse intersystem crossing efficiency of the intermolecular excited state (that is, exciplex state). Most recently, a simple strategy towards high-performance fluorescent OLEDs was reported by stacking p-type hole-transport layer and n-type electron-transport layer, resulting in a planar pn heterojunction configuration similar to their inorganic counterparts, namely light emitting diodes (LEDs). Like this, there is a great and urgent demand for low-cost high-performance light-emitting materials, simple device structure and simple manufacturing process in the field of OLED display. This project will focus on the development of noble metal free organic light-emitting materials and their high performance devices, including development of a new generation of organic light-emitting materials and corresponding host materials with high efficiency and practical lifetimes, investigation of their light emitting mechanisms, structure-property relationships, excited states and their regulation processes, etc. Based on the developed materials and devices, full-color OLED display panels will also be designed and developed.

Synthesis, Structure, and Characterization of Emissive Neutral Dinuclear CuI Complexes with a Tetraphosphane Bridging Ligand

A series of new dinuclear copper complexes with a tetraphosphane bridging ligand, [{(pz4B)Cu}2(µ‐tpbz)] (1), [{(pz2BH2)Cu}2(µ‐tpbz)] (2), and [{(tz2BH2)Cu}2(µ‐tpbz)] (3) [tpbz = 1,2,4,5‐tetrakis(diphenylphosphanyl)benzene, pz4B = tetrakis(pyrazol‐1‐yl)borate, pz2BH2 = bis(pyrazol‐1‐yl)borohydrate, and tz2BH2 = bis(1,2,4‐triazol‐1‐yl)borohydrate], have been synthesized and structurally characterized. The CuI atoms in these complexes are four‐coordinate and adopt a tetrahedral coordination geometry. In each complex, the copper centers are bridged by a tpbz ligand and each CuI is further terminally chelated by a borate diimine anion. The central phenylene ring and the phosphine atoms of the tpbz ligand are essentially planar. The two CuI atoms in each molecule are located above and below the (P2C6H2P2) mean plane, respectively, leading to a chair‐like conformation for the [Cu](P2C6H2P2)[Cu] fragment. The distances between the CuI atoms in each complex are about 8.7 Å. In the solid state, these complexes are emissive and exhibit yellow–orange photoluminescence [emission peaks, λmax = 580 nm (1), 569 nm (2), 540 nm (3)] with lifetimes of 7.4–20.5 µs and quantum yields Φ = 0.07–0.45 at room temperature. Theoretical and experimental results indicate that these complexes have the lowest singlet (S1) state and the lowest triplet (T1) state with very close energy levels, and display thermally activated delayed fluorescence (TADF) at ambient temperature.

Collision Avoidance in a Power Controller and Reactive Routing Protocol in Wireless Mobile Network

This paper introduces a power controller method for Ad Hoc On-Demand Distance Vector (AODV) reactive routing protocol. The proposed algorithm uses adaptive HELLO messages where their transmit periods are adapted according to the instantaneous energy level of the battery. By transmitting HELLO messages at calculated instant, each node stores its neighborhood energy information. The valid(safest) path between sources and destinations is calculated using route request messages. Indeed, the safest path is defined as the route with the maximum energy levels. However, the collision probability occurred by two nodes having very close energy levels is very hight. Then, we investigate, firstly, the collision occurrence probability using Markov Chain modelling of the battery discharge process. After, we introduce a collision avoidance process to a Power Controller and Reactive Routing Protocol (PC-AODV). The performance of the proposed protocol is theoretically canalised and validated by simulation.