We report O−H----S hydrogen-bond (Hbond) formation and its excited-state intramolecular H-bond on/off reaction unveiled by room-temperature phosphorescence (RTP). In this seminal work, this phenomenon is demonstrated with 7-hydroxy-2,2-dimethyl-2,3-dihydro-1Hindene-1-thione (DM-7HIT), which possesses a strong polar (hydroxy)-dispersive (thione) type H-bond. Upon excitation, DM-7HIT exhibits anomalous dual RTP with maxima at 550 and 685 nm. This study found that the lowest lying excited state (S 1 ) of DM-7HIT is a sulfur nonbonding (n) to π* transition, which undergoes O−H bond flipping from S 1 (nπ*) to the non-H-bonded S′ 1 (nπ*) state, followed by intersystem crossing and internal conversion to populate the T′ 1 (nπ*) state. Fast H-bond on/off switching then takes place between T′ 1 (nπ*) and T 1 (nπ*), forming a pre-equilibrium that affords both the T′ 1 (nπ*, 685 nm) and T 1 (nπ*, 550 nm) RTP. The generality of the sulfur H-bond on/off switching mechanism, dubbed a molecule wiper, was rigorously evaluated with a variety of other H-bonded thiones, and these results open a new chapter in the chemistry of hydrogen bonds.
The main goal of this study is to provide systematic elucidation of the parameters that influence S → T intersystem crossing (ISC). Particular attention is paid to: (i) the computation of Sn→ Tm spin-orbit coupling strength based on a non-adiabatic approach, (ii) crucial factors that facilitate ISC, such as the atomic number, ligand structure, and particularly the types of electronic transition, (iii) formulating a discussion on the standpoints of the fundamental photophysical theory. Combining the theoretical and empirical approaches, we then make semi-quantitative assessment of the ISC rate for certain representative transition metal (TM) complexes, the results of which allow us to develop a set of empirical rules that harness ISC for organometallics analogous to El-Sayed's rule for the classic organic compounds. We therefore present a critical and timely theoretical approach with the results matching quantitatively the experimental data, which serves as a prototype to access the photophysics of TM complexes in a facile and precise manner beneficial to researchers in the field of optoelectronics.
Ideal catalysts for the oxygen reduction reaction (ORR) have been searched and researched for decades with the goal to overcome the overpotential problem in proton exchange membrane fuel cells. A recent experimental study reports the application of Pt nanoparticles on the newly discovered 2D material, MXene, with high stability and good performance in ORR. In this work, we simulate the Ti n+1C n T x and the Pt-decorated Pt/v-Ti n+1C n T x (n = 1–3, T = O and/or F) surfaces by first-principles calculations. We focus on the termination effects of MXene, which may be an important factor to enhance the performance of ORR. The properties of different surfaces are clarified by exhaustive computational analyses on the geometries, charges, and their electronic structures. The free-energy diagrams as well as the volcano plots for ORR are also calculated. On the basis of our results, the F-terminated surfaces are predicted to show a better performance for ORR but with a lower stability than the O-terminated counterparts, and the underlying mechanisms are investigated in detail. This study provides a better understanding of the electronic effect induced by the terminators and may inspire realizations of practical MXene systems for ORR catalysis.
A tetradentate bis(pyridylpyrazolate) chelate, L, is assembled by connecting two bidentate 3-(trifluoromethyl)-5-(2-pyridyl)pyrazole chelates at the 6 position of the pyridyl fragment with a phenylamido appendage. This chelate was then utilized in the synthesis of three osmium(II) complexes, namely, [Os(L)(CO)2] (4), [Os(L)(PPh2Me)2] (5), and [Os(L)(PPhMe2)2] (6). Single-crystal X-ray structural analyses were executed on 4 and 5 to reveal the bonding arrangement of the L chelate. Phosphine-substituted derivatives 5 and 6 are highly emissive in both solution and the solid state, and their photophysical properties were measured and discussed on the basis of computational approaches. For application, fabrication and analysis of organic light-emitting diodes (OLEDs) were also carried out. The OLEDs using 5 and 6 as dopants exhibit saturated red emission with maximum external quantum efficiencies of 9.8% and 9.4%, respectively, which are higher than that of the device using [Ir(piq)3] as a red-emitting reference sample. Moreover, for documentation, 5 and 6 also achieve a maximum brightness of 19540 cd·m(-2) at 800 mA·cm(-2) (11.6 V) and 12900 cd·m(-2) at 500 mA·cm(-2) (10.5 V), respectively.
We investigate quantum interference in the transport properties of porphyrinbased molecular devices, and are able to develop a minimal but qualitatively accurate model of conductance based on the maximally localized Wannier functions of just the isolated molecule. We find that transmission at or near the Fermi level can be engineered to vary by orders of magnitude in response to hydrogen tautomerization in the inner ring, a recently developed experimental capability. This allows us to suggest that tape porphyrins can act as molecular-size memory units, displaying many-valued logic. SECTION: Energy Conversion and Storage; Energy and Charge TransportO ne of the emerging areas of research in single-molecule electronics is to employ the wave nature of electrons to control current flow in nanoscale devices. In particular, "quantum interference" in ballistic transport through aromatic systems, especially for the prototypical example, benzene, has been studied extensively both experimentally 1,2 and theoretically. 3−6 It has been shown that the transmission function of benzene can vary by orders of magnitude when the relative orientations of the thiol disubstitution linkers is changed between the para, ortho, and meta configurations. The origin of quantum interference is embedded in the underlying molecular symmetry and electronic structure of the orbitals, and, in particular, in the phase and amplitude of the frontier orbitals of the anchoring atoms linking the molecule to the electrodes. 6,7 The discovery of quantum interference effects has raised a lot of interest in designing single-molecule switches as functional electronic elements. 4,8−10 However, most of the strategies proposed remain to date at the conceptual stage, either lacking practical avenues to control transport or involving drastic conformational changes that are incompatible with realistic device setups. An ideal molecular switch, other than being bistable and reversible, should retain a similar molecular structure and binding strengths to the substrate before and after switching. It has been recently demonstrated that these criteria can be fulfilled by inner-ring hydrogen tautomerization reactions in naphthalocyanines, 11 where tautomerization is induced by electron injection through an scanning tunneling microscope (STM) tip under a bias voltage above the lowest unoccupied molecular orbital (LUMO) resonance. Motivated by this work, we investigate here the porphyrin family of molecules, whose small bandgaps and planar structure render them a very promising candidate for nanoscale device fabrication, 12−15 with the goal of identifying quantum interference effects that can be accurately maneuvered by hydrogen tautomerization. In fact, as one of the most tailorable building blocks for supramolecular systems, porphyrins have long been considered as potential candidates in nanoelectronics application. 16,17 To proceed, we first show how a model based on maximally localized Wannier functions (MLWFs) 18 and the wide-band limit (WBL) approximation acts as a...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.