Controlling the Growth of Molecular Crystal Aggregates with Distinct Linear and Nonlinear Optical Properties

Cs2CO3-Promoted reaction of tertiary bromopropargylic alcohols and phenols in DMF: a novel approach to α-phenoxyketones

The reaction of bromopropargylic alcohols with phenols in the presence of Cs₂CO₃/DMF affords α-phenoxy-α’-hydroxyketones (1:1 adducts) and α,α-diphenoxyketones (1:2 adducts) in up to 92% and 24% yields, respectively. Both products are formed via ring opening of the same intermediates, 1,3-dioxolan-2-ones, generated in situ from bromopropargylic alcohols and Cs₂CO₃.

Luminescent Polymorphic Co-crystals: A Promising Way to the Diversity of Molecular Assembly, Fluorescence Polarization, and Optical Waveguide

The design of molecular optoelectronic materials based on fabricating polymorphs and/or co-crystals has received much recent attention in the fields of luminescence, sensors, nonlinear optics, and so on. If the advantages of the two crystal engineering strategies above were combined, the diversity of self-assembly fashions and the tuning of photofunctional performances would be largely extended. However, such multicomponent examples have still been very limited to date. Herein, we report the construction of luminescent polymorphic co-crystals by assembly of tris(pentafluorophenyl)borane (TPFB) with 9,10-dicyanoanthracene (DCA) and acridine (AC) as paradigms. Different stacking modes and arrangement styles based on identical building block units in polymorphic co-crystals result in adjustable crystalline morphologies and variant photophysical properties (such as fluorescence wavelength, lifetimes, and up-conversion luminescence). The optimized photoluminescence quantum yield (63.1%) and lifetime (57.1 ns) are much higher than those of the pristine assembled units. In addition, two polymorphic co-crystals (DCA@TPFB-1 and AC@TPFB-2) present prominent fluorescence polarization and optical waveguide behaviors due to the highly regulated molecular orientation. Their high one-dimensional luminescence anisotropy (0.652) and low optical waveguide loss (0.0079 dB/μm) outperform most state-of-the-art low-dimensional molecular systems and thus endow them with great opportunities for photonic materials and devices. Therefore, this work not only confirms that constructing polymorphic co-crystals can be an effective way to design new photofunctional materials for luminescence and photonic applications but also discloses a deep understanding on the relationship between variant self-assembled fashions and tunable photofunctional properties of new TPFB-based molecular materials.

Nonlinear Optical Study in a Set of Dibenzylideneacetone Derivatives with Potential for Optical Frequency Conversion

The search for advanced optical materials, in particular, materials with nonlinear optical responses, has, in the last years, experienced substantial growth due to their vast applications in the photonics field. One of those applications is ultra-fast optical frequency conversion, in the optics communications field. Organic compounds have emerged as promising candidates for raw materials to develop nonlinear optical devices, such as optical converters, due to their intrinsic ultra-fast electronic responses. Also, the easy tailoring of organic molecular structures makes organic materials much more appealing than the inorganic ones. In this work, we have performed a linear and nonlinear optical characterization of a set of dibenzylideneacetone derivatives. The nonlinear optical responses investigated correspond to second- and third-order nonlinear processes, namely, first electronic molecular hyperpolarizability and two-photon absorption cross-section, respectively. The value of the first electronic molecular hyperpolarizability, up to 52 cm4·statvolt−1, could be considered a robust value when compared to the short-sized π-electron backbone length of the studied compounds. Such results suggest that these compounds exhibit the potential to be used as optical frequency converters. Quantum chemical calculations were used to predict the theoretical value of the first molecular hyperpolarizability, as well as to simulate the one- and two-photon absorption spectra for all compounds.

Advantageous Units in Antimony Sulfides: Exploration and Design of Infrared Nonlinear Optical Materials

The exploration of infrared (IR) nonlinear optical (NLO) materials remains attractive because of the urgent requirements in the laser field. Meanwhile, the deepened cognition of structure-property relationships is necessary to help guide the exploration of IR NLO materials. So far, the family of antimony sulfides is an important system with a lot of attention, and a series of antimony sulfides are reported. However, it is urgent to reveal how different Sb-S units, like SbS₃, SbS₄, and more complex combinations, affect apparent properties. Here, taking ternary metal antimony sulfides as examples, the sources of some essential optical properties, such as second harmonic generation (SHG) and birefringence, are systematically analyzed through first-principles calculations, and the mechanisms of the performances with various magnitudes are also presented to clarify the structure-property relationships. The results indicate that the SbS₄ unit among antimony sulfides is an advantageous NLO-active unit, which can balance the contradiction between the band gap and SHG response. Introduction of transition metals in the Sb-S anionic frameworks can tune the magnitude of birefringence. Besides, the substitution of a cation from a transition metal to an alkali metal can notably enlarge the band gap and maintain a large SHG response. These design strategies are beneficial to explore potential IR NLO materials with Sb-S units.