provide a rigid molecular environment to boost UOP, [16] whereas their applica tion fields are extremely limited due to the harsh conditions of low temperature. As a preferable choice, the UOP became more intriguing under ambient condi tion recently, and has been achieved by suppressing the nonradiative decay of triplet excitons via several strate gies, such as host-guest doping, [7,[17][18][19][20][21] crystallization, [22][23][24][25][26] the construction of metal-organic frameworks, [27,28] poly merization, [11,29,30] Haggregation, [31,32] and other methods. [33][34][35][36][37][38] In other words, the restriction of the molecular motions such as rotation, vibration, etc. is responsible for the UOP in solid state. However, the structure-property relationship of UOP is still ambigulous due to the complexity of molecular motions. Interestingly, molecular rotor provides a singnificant chance. Hence, by con structing a molecular rotor with UOP character, a fundamental understanding between molecular rotation and UOP property could be illustrated.Fluorine with the similar radius as hydrogen atom has high electronegativity, facilitating the formation of hydrogen bonding. [39] In crystal, the hydrogen bonding in fluorinated compounds can not only restrict the nonradiative decay with increased intermolecular interactions [22] but also adjust the radiative transition for fluorescence improvement. [40] In this work, by rationally tuning the fluoro position on phenylboronic acids, a series of fluorosubstituted phenylboronic acids deriva tives, namely 2,3difluorophenylboronic acid (23FPB), 2,3,4tri fluorophenylboronic acid (234FPB), 2fluorophenylboronic acid (2FPB), and 2,4difluorophenylboronic acid (24FPB) (Figure 1a), showed ultralong emission with lifetimes ranging from 0.36 to 2.50 s. Combining experimental and theoretical studies, it is proposed that the rotation confinement in the molecular rotors was mainly responsible for the prolonged UOP lifetime. With the introduction of fluorine atoms, the intramolecular OH···F hydrogen bonding made varied dihedral angles (θ) between benzene ring and boric acid group, implying that the triplet excitons can be influenced by the rotation in molecular rotors. Further theoretical calculations also confirmed that the rotation between benzene ring and boric acid group was cor responding to the low vibration mode for tuning nonradiative transitions. Therefore, the UOP lifetime can also be adjusted Developing ultralong organic phosphorescence (UOP) materials has become a growing concern. To date, it remains a formidable challenge to prolong the lifetime of ultralong phosphorescence under ambient conditions. A series of fluoro-substituted phenylboronic acid derivatives with UOP feature under ambient conditions is reported here. The UOP lifetime of 2,4-difluorophenylboronic acid (24FBP) crystal is up to 2.50 s, which is the longest emission lifetime among the reported single-component pure organic phosphors. Combining the experimental and theoretical study, upon stabilization of triple...

The transmission distribution of transverse electric wave (TE) through one-dimensional metallic gratings with sub-wavelenghth slits with dielectric added in different positions has been simulated by the FDTD (finite difference time domain) method, the extraordinary transmission can be produced at several special wavelengths. The simulation shows that the guided-mode-like resonance theory is the main reason giving rise to the first peak and the second peak. Based on the guided-mode-like resonance theory, from the Maxwell’s equations,we nade sure that the Fabry Perot resonance is the main cause producing the third peak by the effective index mehod. In a word, the guided-mode resonance theory and the Fabry-Perot-like resonance reveal the physical nature of the extraordinary transmission phenomenon which provides a complete theoretical basis for further study of the extraordinary transmission phenomenon of TE-polarized wave.

To show how to achieve the extraordinary transmission of one-dimensional metallic gratings with sub-wavelenghth slits, the transmission distribution of transverse electric (TE) wave through one-dimensional metallic gratings with sub-wavelenghth slits with a dielectric substance applied on it in different ways has been simulated by the finite-difference time-domain method. The relations between the refractive index of dielectric and the transmission efficiency is elicited from simulation, which show that the extraordinary transmission can be produced at several special wavelengths. Then, a new theory named the guided-mode-like resonance theory is put forward based on the guided-mode resonance theory, which is well suited for the extraordinary transmission under the TE-polarized wave excitation, and it is concluded that the guided-mode-like resonance is the main reason for the extraordinary transmission of TE-polarized wave. Thus, the new theory can explain the problems which cant be explained by the traditional theory. In a word, the guided-mode like resonance theory reveals the physical nature of the extraordinary transmission phenomenon which provides a theoretical basis for the further study of the extraordinary transmission phenomenon.

In this paper, we design a kind of positive and negative gradient refractive index alternating surface and discuss its physical mechanism by the geometrical optics method and the numerical simulation of electromagnetic field. This structure can control the propagation of electromagnetic waves by adjusting some parameters such as refractive gradient. Under certain parameters, electromagnetic waves from space can be confined mainly in the media all the time, or are released into the space after propagating a certain distance in the media. This structure is polarization-independent and wide-band. It means that this structure can be used as a stealth surface by reducing the scattering cross section. Finally, the characteristics of the structure are verified by the numerical simulation.