Nano-scale charge trapping memory based on two-dimensional conjugated microporous polymer.

There is a growing interest in new semiconductor nanostructures for future high-density high-performance flexible electronic devices. Two-dimensional conjugated microporous polymers (2D-CMPs) are promising candidates because of their inherent optoelectronic properties. Here, we are reporting a novel donor-acceptor type 2D-CMP based on Pyrene and Isoindigo (PI) for a potential nano-scale charge-trapping memory application. We exfoliated the PI polymer into ~ 2.5 nm thick nanoparticles (NPs) and fabricated a Metal-Insulator-Semiconductor (MIS) device with PI-NPs embedded in the insulator. Conductive AFM (cAFM) is used to examine the confinement mechanism as well as the local charge injection process, where ultrathin high-κ alumina supplied the energy barrier for confining the charge carrier transport. We have achieved a reproducible on-and-off state and a wide memory window (ΔV) of 1.5 V at a relatively small reading current. The device displays a low operation voltage (V < 1 V), with good retention (104 s), and endurance (103 cycles). Furthermore, a theoretical analysis is developed to affirm the measured charge carriers' transport and entrapment mechanisms through and within the fabricated MIS structures. The PI-NPs act as a nanoscale floating gate in the MIS-based memory with deep trapping sites for the charged carriers. Moreover, our results demonstrate that the synthesized 2D-CMP can be promising for future low-power high-density memory applications.

A Rational Design of Isoindigo-Based Conjugated Microporous n-Type Semiconductors for High Electron Mobility and Conductivity.

The development of n-type organic semiconductors has evolved significantly slower in comparison to that of p-type organic semiconductors mainly due to the lack of electron-deficient building blocks with stability and processability. However, to realize a variety of organic optoelectronic devices, high-performance n-type polymer semiconductors are essential. Herein, conjugated microporous polymers (CMPs) comprising isoindigo acceptor units linked to benzene or pyrene donor units (BI and PI) showing n-type semiconducting behavior are reported. In addition, considering the challenges of deposition of a continuous and homogeneous thin film of CMPs for accurate Hall measurements, a plasma-assisted fabrication technique is developed to yield uniform thin films. The fully conjugated 2D networks in PI- and BI-CMP films display high electron mobility of 6.6 and 3.5 cm2 V-1 s-1 , respectively. The higher carrier concentration in PI results in high conductivity (5.3 mS cm-1 ). Both experimental and computational studies are adequately combined to investigate structure-property relations for this intriguing class of materials in the context of organic electronics.

Mentoring in Times of Crisis and Beyond.

During the global crisis triggered by the COVID-19 pandemic, university programs, meetings, and conferences have moved to virtual settings, with consequent erosion of mentorship opportunities for students and early-career professionals. This calls for mentorship platforms that are adapted to the new landscape in order to bring about a positive change. Our Viewpoint Article shares the perspective of the Transformative Education program and Mentorship Talks initiative at the American University of Beirut in Lebanon, with the aim of providing insights that could stimulate other mentorship platforms.

Metallated Isoindigo-Porphyrin Covalent Organic Framework Photocatalyst with a Narrow Band Gap for Efficient CO2 Conversion.

Photocatalytic CO2 reduction into formate (HCOO-) has been widely studied with semiconductor and molecule-based systems, but it is rarely investigated with covalent organic frameworks (COFs). Herein, we report a novel donor-acceptor COF named Co-PI-COF composed of isoindigo and metallated porphyrin subunits that exhibits high catalytic efficiency (∼50 µmol formate g-1 h-1) at low-power visible-light irradiation and in the absence of rare metal cocatalysts. Density functional theory calculations and experimental diffuse-reflectance measurements are used to explain the origin of catalytic efficiency and the particularly low band gap (0.56 eV) in this material. The mechanism of photocatalysis is also studied experimentally and is found to involve electron transfer from the sacrificial agent to the excited Co-PI-COF. The observed high-efficiency conversion could be ascribed to the enhanced CO2 adsorption on the coordinatively unsaturated cobalt centers, the narrow band gap, and the efficient transfer of the charge originating from the postsynthetic metallation. It is anticipated that this study will pave the way toward the design of new simple and efficient catalysts for photocatalytic CO2 reduction into useful products.

Columnar Mesomorphism of Board-Shaped Perylene, Diketopyrrolopyrrole, Isoindigo, Indigo, and Quinoxalino-Phenanthrophenazine Dyes.

The properties of organic dyes depend as much on their intermolecular interactions as on their molecular structure. While it is generally predictable what supramolecular structure would be ideal for a specific application, the generation of specific supramolecular structures by molecular design and suitable processing methods remains to be a challenge. A versatile approach to different supramolecular structures has been the application of mesomorphism in conjunction with alignment techniques and self-assembly at interfaces. Reviewed here is the columnar mesomorphism of board-shaped dyes perylene, indigo, isoindigo, diketopyrrolopyrrole, and quinoxalinophenanthrophenazine. They generate a larger number of different supramolecular structures than conventional disc-shaped (discotic) mesogens because of their non-circular shape and directional intermolecular interactions. The mesomorphism of all but the perylene derivatives is systematically and comprehensively covered for the first time.

Perception, attitude, practice and barriers towards medical research among undergraduate students.

BACKGROUND: Early exposure to medical research, specifically at the undergraduate level, contributes in building a solid medical education for students. In 2014, the Medical Research Volunteer Program (MRVP) was established at the American University of Beirut (AUB). This program provides undergraduate students with the opportunity to be involved in ongoing medical research projects, on a voluntary basis. Little is known about undergraduates' outlook on medical research and the challenges they face. The aim of this study was to assess, among AUB undergraduate students, the perception, attitude, practice and barriers towards medical research, as well as to identify factors affecting them, such as background characteristics and research involvement. METHODS: A cross sectional study was carried out at AUB, where undergraduate students enrolled in specific chosen classes were surveyed in spring 2019 via paper based questionnaires. Close-ended questions assessed students' attitude, perception, practice and barriers towards medical research using a 5-point likert scale. Moreover, demographic characteristics and research involvement information were collected. RESULTS: Five hundred and twenty three students were surveyed. About half of the students were premedical students (51.5%), and only 43.6% of them were aware of the medical research program at their university. The average attitude, perception, practice and barriers scores were found to be 3.58, 4.35, 3.58 and 2.60, respectively (on a scale from 1 to 5). Students found the lack of mentoring and guidance to be the main barrier in conducting medical research. CONCLUSION: Our findings reveal that students express interest towards medical research and recognize its importance. A medical research program at the undergraduate level is indispensable in guiding students in their future career endeavors. Therefore, research programs should be constantly monitored to assure a research-oriented environment within institutions.

Self-Assembly of Board-Shaped Diketopyrrolopyrrole and Isoindigo Mesogens into Columnar π-π Stacks.

Diketopyrrolopyrrole and isoindigo are commercially important dyes that have recently found broad application as electron acceptor and light-absorbing groups in organic semiconductors. Their self-assembly into specific supramolecular structures to control optoelectronic properties has been hampered by limited options for substitution and their high propensity for crystallization. Reported here is a molecular design that directs self-assembly into previously elusive columnar mesophases of π-π stacking cores. Although attachment of bis(trisoctyloxyphenyl)-1,3,5-triazine groups to both ends of diketopyrrolopyrrole-thiophene and isoindigo cores generated mesomorphic dyes of similar overall shapes and dimensions, distinct differences in their mesomorphism and optoelectronic properties were observed.

Medical Research Volunteer Program (MRVP): innovative program promoting undergraduate research in the medical field.

BACKGROUND: Most educational institutions lack a structured system that provides undergraduate students with research exposure in the medical field. The objective of this paper is to describe the structure of the Medical Research Volunteer Program (MRVP) which was established at the American University of Beirut, Lebanon, as well as to assess the success of the program. METHODS: The MRVP is a program that targets undergraduate students interested in becoming involved in the medical research field early on in their academic career. It provides students with an active experience and the opportunity to learn from and support physicians, clinical researchers, basic science researchers and other health professionals. Through this program, students are assigned to researchers and become part of a research team where they observe and aid on a volunteer basis. This paper presents the MRVP's four major pillars: the students, the faculty members, the MRVP committee, and the online portal. Moreover, details of the MRVP process are provided. The success of the program was assessed by carrying out analyses using information gathered from the MRVP participants (both students and faculty). Satisfaction with the program was assessed using a set of questions rated on a Likert scale, ranging from 1 (lowest satisfaction) to 5 (highest satisfaction). RESULTS: A total of 211 students applied to the program with a total of 164 matches being completed. Since the beginning of the program, three students have each co-authored a publication in peer-reviewed journals with their respective faculty members. The majority of the students rated the program positively. Of the total number of students who completed the program period, 35.1 % rated the effectiveness of the program with a 5, 54.8 % rated 4, and 8.6 % rated 3. A small number of students gave lower ratings of 2 and 1 (1.1 % and 0.4 %, respectively). CONCLUSION: The MRVP is a program that provides undergraduate students with the opportunity to learn about research firsthand as they volunteer and aid in different research projects. This program also provides faculty members with the help to conduct their research projects and opportunity to influence future generations. It was shown that so far the MRVP has been successful in reaching its goals, for both students and faculty.

Columnar mesomorphism of fluorescent board-shaped quinoxalinophenanthrophenazine derivatives with donor-acceptor structure.

Quinoxalino[2',3':9,10]phenanthro[4,5-abc]phenazine (QPP) dyes have been studied as electron acceptor materials, fluorophores, and building blocks for self-organizing organic semiconductors. Condensation of tetraketopyrene with electron-rich diamino-terphenylene and -triphenylene derivatives generates new donor-acceptor QPP derivatives that display columnar mesomorphism over wide ranges of temperature; are fluorescent in solution, liquid crystal, and solid phases; and have electron acceptor properties. Also reported are the synthesis and properties of the first diamino-(tetraalkoxy)triphenylene as a valuable new synthon.

Phase transitions and structures of novel pyrenes potentially useful in photovoltaic applications.

A series of conjugated compounds, 6,7,15,16-tetrakis(alkylthio)quinoxalino[2',3':9,10]phenanthro[4,5-abc]phenazine (TQPP-[SC(n)](4)) (n = 6, 8, 10, and 12), which display p-channel characteristics was synthesized. These materials show promise for use in liquid crystalline photovoltaic applications. To determine their applicability, the different phase structures and transitions of these compounds were studied with differential scanning calorimetry (DSC), polarized light microscopy (PLM), wide-angle X-ray diffraction (WAXD), selected area electron diffraction (SAED), and Fourier transform infrared spectroscopy (FT-IR). Using TQPP-[SC(12)](4) as a model compound, DSC and 1D WAXD results showed that this compound possesses four crystalline, but no liquid crystalline, phases. Based on structural results obtained from 2D WAXD experiments on oriented samples and SAED patterns from single crystals, the unit cell of the lowest temperature TQPP-[SC(12)](4) crystalline phase (K(1)) was determined to be monoclinic with dimensions of a = 1.87 nm, b = 0.53 nm, c = 3.51 nm, and beta = 96.2 degrees . With increasing temperature, the K(1) phase transformed to other crystalline phases which all were monoclinic with different crystallographic parameters. The arrangement of the TQPP-[SC(12)](4) rigid fused rings changed only slightly in these crystalline phases, yet the conformation of the alkyl chains attached to the rigid cores changed significantly at the phase transitions. For the other TQPP-[SC(n)](4) compounds, only two phase transitions could be identified. It was determined that the transition temperature can be tuned by modifying the attached alkyl chains at the four corners of the rigid fused rings. One-dimensional WAXD studies indicated that the condensed state phase transitions of these compounds were all crystal-crystal transitions. Although single crystals will provide the highest charge carrier mobility, they are very difficult to grow and incur a high cost in production. On the other hand, liquid crystalline phases are preferred for the ease of processing and reasonable performance in change carrier mobility. Therefore, in order to achieve liquid crystalline phases in these compounds, as desired for their application as organic photovoltaic materials, additional modifications to the alkyl chains and their locations are necessary.

Effect of chain length on the photophysical properties of pyrene-based molecules substituted with extended chains.

The important role played by organic conjugated compounds in the fields of electronics and optoelectronics has led to a vast field of research concerned with synthesizing various complex structures where pi-pi stacking plays a vital role. Pyrene-based molecules are examples of compounds which allow efficient charge transfer through pi-pi molecular stacking. Photophysical studies of such compounds have shown similar behavior as that of pyrene, even though they bear two additional conjugated rings and four long alkyl chains. Chain length may have played an effective role in influencing the pi-pi molecular stacking of such molecules. In continuation of our earlier work (Moustafa, R. M.; Degheili, J. A.; Patra, D.; Kaafarani, B. R. J. Phys. Chem. A 2008, 113, 1235-1243), we hereby synthesize and investigate the role of the chain lengths on the photophysical aspects of 2,11-di-tert-butyl-6,7,15,16-tetrakis(alkoxy/alkythio)quinoxaline-[2',3':9,10]phenanthro[4,5-abc]phenazine, TQPP-[t-Bu](2)-[XR](4) (X = O, S; R = C(n)H(2n+1)). Various photophysical parameters such as Stokes shift, fluorescence lifetime, fluorescence quantum yield, and radiative and nonradiative rate constants are evaluated for TQPP-[t-Bu](2)-[OR](4) and TQPP-[t-Bu](2)-[SR](4) in tetrahydrofuran. The variation of the Stokes shift, fluorescence quantum yield, and lifetime are also correlated with the number of carbons in the alkyl chain R for TQPP-[t-Bu](2)-[OR](4) and TQPP-[t-Bu](2)-[SR](4).

Synthesis and detailed photophysical studies of pyrene-based molecules substituted with extended chains.

Applications of conjugated organic compounds in the field of electronics and optoelectronics and of pyrene derivatives as fluorescent probes are well established. The synthesis of the novel pyrene-based 2,11-di-tert-butyl-6,7,15,16-tetrakis(alkoxy/alkythio)quinoxaline[2',3':9,10]phenanthro[4,5-abc]phenazine, TQPP-[t-Bu](2)-[XR](4) (X = O, S; R = C(n)H(2n+1)), is reported along with an in-depth spectroscopic characterization and evaluation of their photophysical properties. Despite their larger core size, the reported TQPP materials showed similar fluorescence behavior to that of pyrene itself, with no significant shift in their fluorescence peak. The fluorescence spectra showed peaks corresponding to the monomer and to the excimer. Even though these TQPP compounds showed poor solubility in various solvents, their solvatochromism could be investigated in different solvents ranging from polar solvents such as methanol to nonpolar solvents such as cyclohexane; Stokes shifts, fluorescence lifetimes, fluorescence quantum yields, as well as radiative and nonradiative rate constants are determined for four of these TQPP materials in various solvents. Quantum yields were found to be low for these TQPP compounds in solvents such as tetrahydrofuran (THF), whereas they were relatively higher in cyclohexane and dioxane. Monomer to excimer intensity ratio versus gross solvent scale (E(T)30) and orientation polarizabilty (Delta f) were correlated. Although TQPP-[t-Bu](2)-[XR](4) displayed similar fluorescent emission and excitation behavior as that of pyrene, a relatively smaller lifetime was observed for these compounds compared to that of pyrene.

Synthesis, ionisation potentials and electron affinities of hexaazatrinaphthylene derivatives.

Several hexaazatrinaphthylene derivatives and a tris(thieno)hexaazatriphenylene derivative have been synthesised by reaction of the appropriate diamines with hexaketocyclohexane. The crystal structure of 2,3,8,9,14,15-hexachloro-5,6,11,12,17,18-hexaazatrinaphthylene has been determined by X-ray diffraction; this reveals a molecular structure in good agreement with that predicted by density functional theory (DFT) calculations and pi-stacking with an average spacing between adjacent molecular planes of 3.18 A. Solid-state ionisation potentials have been measured by using UV photoelectron spectroscopy and fall in the range of 5.99 to 7.76 eV, whereas solid-state electron affinities, measured using inverse photoelectron spectroscopy, vary in the range -2.65 to -4.59 eV. The most easily reduced example is a tris(thieno)hexaazatriphenylene substituted with bis(trifluoromethyl)phenyl groups; DFT calculations suggest that the highly exothermic electron affinity is due both to the replacement of the outermost phenylene rings of hexaazatrinaphthylene with thieno groups and to the presence of electron-withdrawing bis(trifluoromethyl)phenyl groups. The rather exothermic electron affinities, the potential for adopting pi-stacked structures and the low intramolecular reorganisation energies obtained by DFT calculations suggest that some of these molecules may be useful electron-transport materials.

Altering the emission behavior with the turn of a thiophene ring: the photophysics of condensed ring systems of alternating benzenes and thiophenes.

Six aromatic compounds with embedded thiophenes differing in the number of rings (2-5) and thiophene orientation along the long axis of the molecule (syn, anti) were investigated. Photophysical properties, steady-state absorption, fluorescence, phosphorescence, lifetimes, quantum yields, and a comprehensive time-resolved spectroscopic analysis (femtosecond and nanosecond transient absorption spectroscopy) have been studied as a function of molecular structure.

Design, synthesis, and properties of new derivatives of pentacene.

Stable, soluble ethynylated derivatives of pentacene (9a-c) were synthesized, and the ethynyl moieties on the terminal rings were used to tune the electronic properties of these compounds. Their oxidation potentials are higher and their reduction potentials are lower than those of pentacene. The HOMO-LUMO gaps are among the lowest reported for pentacene derivatives.

Vibronic coupling in organic semiconductors: the case of fused polycyclic benzene-thiophene structures.

The nature of vibronic coupling in fused polycyclic benzene-thiophene structures has been studied using an approach that combines high-resolution gas-phase photoelectron spectroscopy measurements with first-principles quantum-mechanical calculations. The results indicate that in general the electron-vibrational coupling is stronger than the hole-vibrational coupling. In acenedithiophenes, the main contributions to the hole-vibrational coupling arise from medium- and high-frequency vibrations. In thienobisbenzothiophenes, however, the interaction of holes with low-frequency vibrations becomes significant and is larger than the corresponding electron-vibrational interaction. This finding is in striking contrast with the characteristic pattern in oligoacenes and acenedithiophenes in which the low-frequency vibrations contribute substantially only to the electron-vibrational coupling. The impact of isomerism has been studied as well.

High charge-carrier mobility in an amorphous hexaazatrinaphthylene derivative.

An isomeric mixture of a tris(pentafluorobenzyl ester) derivative of hexaazatrinaphthylene forms stable amorphous films with an effective charge-carrier mobility of 0.02 cm2/Vs, while the pure 2,8,15-isomer exhibits widely differing morphologies and carrier mobilities (0.001-0.07 cm2/Vs), depending critically on the processing conditions.

Synthesis of the anti and syn isomers of thieno[f,f ']bis[1]benzothiophene. Comparison of the optical and electrochemical properties of the anti and syn isomers.

We report isomer-pure synthesis of thieno[2,3-f:5,4-f ']bis[1]benzothiophene and thieno[3,2-f:4,5-f ']bis[1]benzothiophene, the anti and syn isomers of a pentacyclic compound consisting of alternating thiophene and benzene rings. The optical and electrochemical properties of both are reported. In the anti isomer, the ribbonlike embedding of three thiophene units leads to a near-planar molecule with favorable pi-pi stacking behavior in the solid state as shown by X-ray crystal structure analysis.

Efficient isomer-pure synthesis of a benzo[b]thiophene analogue of pentacene.

Isomer-pure thieno[3,2-f:4,5-f ']bis[1]benzothiophene (2, n = 2) has been synthesized in an efficient four step approach without column chromatography.

Photoaddition reactions of acetylene and butadiyne derivatives to benzodithiophene.

The photochemical [2pi +2pi] cycloaddition of dimethyl acetylenedicarboxylate to benzo[1,2-b:4,5-b']dithiophene has been used to synthesize substituted cyclobuta[b]thieno[2,3-f][1]benzothiophene. The first [2pi + 2pi] photocycloaddition reaction of a series of butadiynes to benzodithiophene is reported to yield regioselective and acetylene-substituted cyclobutene derivatives containing an aromatic thiophene moiety.