A comprehensive review on the recent progress of black silicon research and its applications in solar cell technologies.

Invisibility cloaks, a subject that usually occurs in science fiction and myths, have attracted wide interest recently because of their possible realization. The biggest challenge to true invisibility is known to be the cloaking of a macroscopic object in the broad range of wavelengths visible to the human eye. Here we experimentally solve this problem by incorporating the principle of transformation optics into a conventional optical lens fabrication with low-cost materials and simple manufacturing techniques. A transparent cloak made of two pieces of calcite is created. This cloak is able to conceal a macroscopic object with a maximum height of 2 mm, larger than 3500 free- Significant progress has been made during the exploration of invisibility cloak. The first theoretical model of a transformation-based cloak [3] required extreme values of the constitutive parameters of materials used and can only work within a very narrow frequency band [3,15]. Schurig et al. overcame the first flaw by using simplified constitutive parameters at microwaves based on metamaterial technologies [6]. To bypass the bandwidth limitation and push the working frequencies into the optical spectrum, it has been proposed that an object sitting on a flat ground plane can be made invisible under a fully dielectric gradient-refractive-index "carpet" cloak generated by quasiconformal mapping [5]. This carpet cloak model has led to a lot of subsequent experiments in both microwave [8,13] and infrared frequencies [9][10][11]14]. However, a serious limitation of carpet cloaks was recently pointed out: the quasiconformal mapping strategy will generally lead to a lateral shift of the scattered wave, whose value is comparable to the height of the hidden object, making the object detectable [16]. Furthermore, all previous experiments of invisibility in the optical spectrum, from infrared [9-11, 14] to visible [7,12] frequencies, were demonstrated under a microscope, hiding objects with sizes ranging from the order of 1 wavelength [7,[9][10][11]14] to approximately 100 wavelengths [12]. How to "see" the invisibility effect with the naked eye, i.e. to cloak a macroscopic object in visible light, is still a crucial challenge. In addition, most previous optical cloaks [7,[9][10][11]14] required complicated nano-or microfabrication, where the cloak, the object to be hidden, and the surrounding medium serving as the background were all fabricated in one structure. Thus they could not be easily separated from their embedded structures and transferred elsewhere to cloak other objects. These limitations, such as detectability, inadequate capacity to hide a large object, and nonportability, must be addressed before an optical cloak becomes practical. 2The above limitations boil down to two difficulties in the fabrication of cloak materialsanisotropy and inhomogeneity. The previously proposed quasiconformal mapping strategy attempted to solve anisotropy in order to facilitate metamaterial implementation [5]. However, in conventional optical lens fab...

Understanding the molecular origins of the optoelectronic properties of fluorophores provides rational guidelines for chemists to synthesize better-performing dyes. Factors affecting the UV−vis absorption spectral shift, molar extinction coefficients, and Stokes shift of fluorophores are herein examined at the molecular level, via both (time-dependent) density functional theory-based calculations and the empirical harmonic-oscillator-stabilization-energy (HOSE) and bond-lengthalternation (BLA) models. The importance of these factors is discussed using six coumarin dyes as exemplars. In particular, a special focus is devoted to the Stokes shift, a critical parameter in fluorophores. It is demonstrated that incorporating a "rotational" substituent in a fluorophore molecule with tailored steric hindrance effects and resonance effects leads to a substantial increase in the Stokes shift, not only in coumarins but also in other chemical dye families: boron-dipyrromethenes (BODIPYs), cyanines, and stilbenes. Structure−property relationships concerning the rotational substituent are discussed in detail with examples of several dye families. These findings lead to the proposal of molecular design criteria that enable one to tune the Stokes shift. Such criteria provide a foundation for the molecular engineering of fluorophores with improved optoelectronic properties.

Solid-state organic photoswitches with reversible luminescence modulation property are highly attractive because of their wide prospects in advanced photonic applications, such as optical data storage, anticounterfeiting and bioimaging. Yet, developing such materials has long been a significant challenge. In this work, we construct an efficient solid-state photoswitch based on a spiropyran-functionalized distyrylanthracene derivative (DSA-2SP) that exhibits exceptional reversible absorption/luminescence modulation ability. Efficient photoswitching between DSA-2SP and its photoisomer DSA-2MC are facilitated by large free volumes induced by nonplanar molecular structures of DSA moieties, as well as the intramolecular hydrogen bonds between the DSA and MC moieties. Consequently, the excellent solid-state photochromic property of DSA-2SP is highly applicable as both anticounterfeiting inks and super-resolution imaging agents.

The twisted intramolecular charge transfer (TICT) mechanism and twists beyond TICT have guided the creation of numerous bright and sensitive fluorophores. We reviewed the structure–property relationships of these dyes with representative examples.

Coumarin derivatives are used in a wide range of applications, such as dye-sensitized solar cells (DSCs) and dye lasers, and have therefore attracted considerable research interest. In order to understand the molecular origins of their optoelectronic properties, molecular structures for 29 coumarin laser dyes are statistically analyzed. To this end, data for 25 compounds were taken from the Cambridge Structural Database and compared with data for four new crystal structures of coumarin laser dyes [Coumarin 487 (C(19)H(23)NO(2)), Coumarin 498 (C(16)H(17)NO(4)S), Coumarin 510 (C(20)H(18)N(2)O(2)), and Coumarin 525 (C(22)H(18)N(2)O(3))], which are reported herein. The competing contributions of different resonance states to the bond lengths of the 4- and 7-substituted coumarin laser dyes are computed based on the harmonic oscillator stabilization energy model. Consequently, a positive correlation between the contribution of the para-quinoidal resonance state and the UV-vis peak absorption wavelength of these coumarins is revealed. Furthermore, the perturbations of optoelectronic properties, owing to chemical substituents in these coumarin laser dyes, are analyzed: it is found that their UV-vis peak absorption and lasing wavelengths experience a red shift, as the electron-donating strength of the 7-position substituent increases and/or the electron-withdrawing strength of the 3- or 4-position substituent rises; this conclusion is corroborated by quantum-chemical calculations. It is also revealed that the closer the relevant substituents align with the direction of the intramolecular charge transfer (ICT), the larger the spectral shifts and the higher the molar extinction coefficients of coumarin laser dyes. These findings are important for understanding the ICT mechanism in coumarins. Meanwhile, all structure-property correlations revealed herein will enable knowledge-based molecular design of coumarins for dye lasers and DSC applications.

The need for detecting and labelling environmentally and biologically important analytes has driven considerable research efforts in developing fluorescent probes. During the sensing process, molecular motions (i.e., molecular rotations or vibrations) of a flexible fluorescent probe can be significantly altered by its embedding micro-environment or analyte, thereby leading to substantial changes in readout signals. Motion-induced change in emission (MICE) can be utilized as an effective sensing mechanism. However, in comparison to the well-understood sensing mechanisms, such as photo-induced electron transfer (PET), intramolecular charge transfer (ICT), aggregation-induced emission (AIE) and disaggregation-induced emission (DIE), MICE has not been systematically discussed to date. In this tutorial review, we will summarize the concept and mechanisms of MICE for developing single-molecular fluorescent probes, present unique advantages of MICE based sensors, demonstrate their various applications, and discuss technical challenges in this field. We expect that this review will promote a deeper understanding of MICE and facilitate the development of novel MICE based probes.

Insufficient brightness of fluorophores poses a major bottleneck for the advancement of super-resolution microscopes. Despite being widely used, many rhodamine dyes exhibit sub-optimal brightness due to the formation of twisted intra­molecular charge transfer (TICT) upon photoexcitation. Herein, we have developed a new class of quaternary piperazine-substituted rhodamines with outstanding quantum yields (Φ = 0.93) and superior brightness (ε × Φ = 8.1 × 104 L·mol–1·cm–1), by utilizing the electronic inductive effect to prevent TICT. We have also successfully deployed these rhodamines in the super-resolution imaging of the microtubules of fixed cells and of the cell membrane and lysosomes of live cells. Finally, we demonstrated that this strategy was generalizable to other families of fluorophores, resulting in substantially increased quantum yields.