Under local plasmonic excitation, Raman images of single molecules can now surprisingly reach subnanometer resolution. However, its physical origin has not been fully understood. Here we report a quantum-mechanical description of the interaction between a molecule and a highly confined plasmonic field. We show that when the spatial distribution of the plasmonic field is comparable to the size of the molecule, the optical transition matrix of the molecule becomes dependent on the position and distribution of the plasmonic field, resulting in a spatially resolved high-resolution Raman image of the molecule. The resonant Raman image reflects the electronic transition density of the molecule. In combination with first-principles calculations, the simulated Raman image of a porphyrin derivative adsorbed on a silver surface nicely reproduces its experimental counterpart. The present theory provides the basic framework for describing linear and nonlinear responses of molecules under highly confined plasmonic fields.

Organic fluorescent emitters with narrowband emissions are highly desirable for high‐resolution organic light‐emitting diode (OLED) display technology. In principle, this can be achieved by specifically controlling the intrinsic structural relaxation and vibronic coupling in the excited state. Here, a design strategy to realize narrowband emission of organic fluorescent emitters is proposed by significantly enhancing the low‐frequency vibronic coupling strength (Λ) while simultaneously reducing the high‐frequency Λ of the commonly involved stretching modes. The quinolino‐[3,2,1‐de]acridine‐5,9‐dione (QAO) species is found to be directly associated with this design principle. By introducing single bond‐linked peripheral moieties into the QAO core, the constructed QAO derivatives are shown to exhibit better performance, by achieving a full width at half‐maximum of 23 nm/0.13 eV in toluene for the narrowest band as well as 27 nm/0.15 eV in doped devices, with negligible dependence on the doping concentrations. The maximum external quantum efficiency of the fabricated blue OLED is 17.5%.

We present a general theory to model the spatially resolved non-resonant Raman images of molecules. It is predicted that the vibrational motions of different Raman modes can be fully visualized in real space by tip-enhanced non-resonant Raman scattering. As an example, the non-resonant Raman images of water clusters were simulated by combining the new theory and first-principles calculations. Each individual normal mode gives rise its own distinct Raman image, which resembles the expected vibrational motions of the atoms very well. The characteristics of intermolecular vibrations in supermolecules could also be identified. The effects of the spatial distribution of the plasmon as well as nonlinear scattering processes were also addressed. Our study not only suggests a feasible approach to spatially visualize vibrational modes, but also provides new insights in the field of nonlinear plasmonic spectroscopy.

The electroluminescence (EL) of molecules confined inside a nanocavity in the scanning tunneling microscope possesses many intriguing but unexplained features. We present here a general theoretical approach based on the density-matrix formalism to describe the EL from molecules near a metal surface induced by both electron tunneling and localized surface plasmon excitations simultaneously. It reveals the underlying physical mechanism for the external bias dependent EL. The important role played by the localized surface plasmon on the EL is highlighted. Calculations for porphyrin derivatives have reproduced corresponding experimental spectra and nicely explained the observed unusual large variation of emission spectral profiles. This general theoretical approach can find many applications in the design of molecular electronic and photonic devices.

Harvesting non-emissive spin-triplet charge-transfer (CT) excitons of organic semiconductors is fundamentally important for increasing the operation efficiency of future devices.H ere we observe thermally activated delayed fluorescence (TADF) in a1 :2 CT cocrystal of trans-1,2-diphenylethylene (TSB) and 1,2,4,5-tetracyanobenzene (TCNB). This cocrystal system is characterized by absorption spectroscopy, variable-temperature steady-state and time-resolved photoluminescence spectroscopy, single-crystal X-ray diffraction, and first-principles calculations.T hese data reveal that intermolecular CT in cocrystal narrows the singlet-triplet energy gap and therefore facilitates reverse intersystem crossing (RISC) for TADF.T hese findings open up an ew way for the future design and development of novel TADF materials.Improving the exciton-utilizing efficiency is an important issue in organic electronics.L ots of research attention has been focused on designing new efficient organic light-emitting diode (OLED), organic light-emitting transistor (OLET), and organic photovoltaic (OPV) cell materials. During the state-of-the-art device operations,t he generated singlet and triplet excitons from charge recombination have ar atio of 1:3a ccording to the spin statistics. [1,2] For fluorescence-based devices,o nly singlet excitons are spinallowed, and light can be emitted with am aximum excitonutilizing efficiency of 25 %. In contrast, phosphorescencebased devices can utilize nearly 100 %excitons through the so called "heavy atom effect" -e nhanced intersystem crossing (ISC) from the singlet to the triplet state.H owever,s uch devices commonly use noble-metals,such as Ir III and Pt II ,and their high cost, scarcity,a nd toxicity hinder their long-term development and industrial applications. [3,4] To date,m uch effort has been devoted to breaking through the exciton statistics limit by using rare-earth-metal-free materials. [5,6] To improve the exciton-utilizing efficiency,h arvesting nonemissive triplet excitons of organic semiconductors is of fundamental interest. However,p ure organic compounds hardly exhibit room temperature phosphorescence (RTP) for two reasons:G round-state excimers may quench at high concentration or in the solid state due to aggregation effects; and triplet-state excimers are easy to quench due to their sensitivity to ambient conditions,i ncluding oxygen gas and humidity. [7][8][9] Alternatively,s cientists have been working on harvesting excitons based on reversed ISC (RISC) between different excited state manifolds.A dachisg roup proposed the thermally activated delayed fluorescence (TADF) mechanism through organic molecular design, wherein the system evolves from at riplet excited state to the lowest singlet excited state (S 1 )via RISC. [10,11] Masgroup discovered ahot exciton RISC mechanism with hybridized local and charge transfer (HLCT) character. [12,13] In both cases,the CT nature of excited states induces spatial separation in orbitals and as mall singlet-triplet energy gap (DE ST ,u sually appro...

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Chiral nanostructures exhibited distinctive functions and attractive applications in complex biological systems, which demonstrated the subject of many outstanding research studies. In this work, various hierarchical composite film nanostructures were designed via supramolecular self-assembly using chiral amphiphilic glutamate derivatives and achiral porphyrin derivatives and their macroscopic enantioselective recognition properties were investigated. We have found that intermolecular hydrogenbonding interactions between water (donor and acceptor) and N,Ndimethylformamide (DMF) as well as chloroform (CHCl 3 ) (acceptor only) and DMF could subtly alter the molecular packing and significantly affected the supramolecular self-assembled nanostructures and triggered circular dichroism (CD) signal reversal. Present research work exemplified a feasible method to fabricate chiral flower-like and brick-like nanostructure films in different mixed solvents and large-scale chiral transfer from the molecular level to complex structures, which also provided a facile approach to identify certain L-/D-amino acids by means of contact angle detection using present obtained self-assembled composted films.

We performed a combined experimental and theoretical study of the C1s Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectroscopy and X-ray Photoelectron Spectroscopy in the gas phase of two polycyclic aromatic hydrocarbons (phenanthrene and coronene), typically formed in combustion reactions. In the NEXAFS of both molecules, a double-peak structure appears in the C1s → LUMO region, which differ by less than 1 eV in transition energies. The vibronic coupling is found to play an important role in such systems. It leads to weakening of the lower-energy peak and strengthening of the higher-energy one because the 0 - n (n > 0) vibrational progressions of the lower-energy peak appear in nearly the same region of the higher-energy peak. Vibrationally resolved theoretical spectra computed within the Frank-Condon (FC) approximation and linear coupling model agree well with the high-resolution experimental results. We find that FC-active normal modes all correspond to in-plane vibrations.