Position of Biphenyl Group Turning The Structure and Photophysical Property of D-π-π-A Prototype Fluorescent Material

Three novel D-π-π-A prototype compounds, namely, (E)-2-(3-([1,1'-biphenyl]-2-yl)-1-(9H-fluoren-2-yl) allylidene) malononitri-le (2-BAM), (E)-2-(3-([1,1'-biphenyl]-3-yl)-1-(9H-fluoren-2-yl)allylidene) malononitri-le (3-BAM), (E)-2-(3-([1,1'-biphenyl]-4-yl)-1-(9H-fluoren-2-yl)allylidene) malononitri-le (4-BAM) were synthesized. Furthermore, the structures and photophysical properties of three compounds were compared. Molecules of 2-BAM were packed into a 1D column structure with H-aggregation. However, both of 3-BAM and 4-BAM were packed into 3D layer structures with J-aggregation, respectively. Although three compounds all showed highly twisted molecular geometries, their molecular packing and intermolecular interactions were different. Because of the differences in electronic structures of molecules, the three compounds displayed different emission behaviors in solid and dilute solution. This study indicated that changing the position of biphenyl groups is an effective way to turn the structures and photophysical properties of such D-π-π-A prototype fluorescent material.

Photophysical property and optical nonlinearity of cyclo[18]carbon (C18) precursors, C18-(CO)n (n = 2, 4, and 6): Focusing on the effect of carbonyl (-CO) groups

Considering their remarkable chemical stability, the precursors of cyclo[18]carbon (C18), C18-(CO)n (n = 2, 4, and 6), have more practical significance than the elusive C18 ring. In the present paper, the electronic spectrum and (hyper)polarizability of the C18-(CO)n (n = 2, 4, and 6) are studied by theoretical calculations and analyses for revealing the utility of introduction of carbonyl (-CO) groups on molecular optical properties. The analysis results show that the successive introduction of -CO groups leads to red-shift of the absorption spectrum, but maximum absorption of all molecules is mainly due to the charge redistribution caused by electron transition within C18 ring. Except for the vanishing first hyperpolarizability of C18-(CO)6 results from its octupolar character, the (hyper)polarizabilities of the precursors present an ascending trend with the increase of -CO groups in the molecule, and the higher-order response properties are more sensitive to the number of -CO groups. By means of (hyper)polarizability density analysis and (hyper)polarizability contribution decomposition, the fundamental reasons for the difference of (hyper)polarizability of different molecules were systematically discussed from the perspectives of physical and structural origins, respectively. As to the frequency dispersions under the incident light, the significant optical resonances were found on the hyperpolarizability of molecules C18-(CO)n (n = 2, 4, and 6), which contrast with the fact that it has inconspicuous influences on molecular polarizability.

Elastic organic crystals with ultralong phosphorescence for flexible anti-counterfeiting

Ultralong organic phosphorescence (UOP) crystals have attracted increased attention due to the distinct photophysical property of a long-lived lifetime. However, organic crystals are generally brittle, leading to a serious problem for their application in flexible technology. Herein, we report three types of elastic organic crystals (EOCs) with ultralong phosphorescence via introducing halogen atoms (Cl, Br, I) into π-conjugated phosphorescent molecules. Especially, the crystal containing iodine atoms displayed both excellent elasticity (ε = 3.01%) and high phosphorescent efficiency (ΦPh = 19.1%) owing to the strong halogen bonds. Taking advantage of its highly efficient UOP and excellent elasticity, we successfully used a DCz4I crystal for anti-counterfeiting application. These findings may provide guidance for the development of elastic crystals with afterglow and expand the scope of potential applications on flexible materials.

A Novel Deep Blue LE-Dominated HLCT Excited State Design Strategy and Material for OLED

Deep blue luminescent materials play a crucial role in the organic light-emitting diodes (OLEDs). In this work, a novel deep blue molecule based on hybridized local and charge-transfer (HLCT) excited state was reported with the emission wavelength of 423 nm. The OLED based on this material achieved high maximum external quantum efficiency (EQE) of 4% with good color purity. The results revealed that the locally-excited (LE)-dominated HLCT excited state had obvious advantages in short wavelength and narrow spectrum emission. What is more, the experimental and theoretical combination was used to describe the excited state characteristic and to understand photophysical property.