Structural−Property Relationship in Pyrazino[2,3-g]quinoxaline Derivatives: Morphology, Photophysical, and Waveguide Properties

Abstract

The objective of this contribution is to achieve crystalline one-dimensional organic micro/nanostructures by self-assembling for active waveguides and other optoelectronic nanodevices. To improve solid emitting performance for highly efficient waveguide fibers, our strategy here is to adopt nonplanar conjugated segments to minimize unfavorably intermolecular fluorescent quenching in solid state; meanwhile, long alkyl chains are added as structural group that controls molecular packing. With this intention, a series of molecules based on pyrazino[2,3-g]quinoxaline (PyQ) units were developed. The effects of the molecular geometry and symmetry on their optical properties, crystal dimensions, liquid crystals, and active waveguide properties were studied in detail to understand the structure−property relationship of organic conjugated molecules, which is of vital importance to rational design for organic self-assemblies toward optoelectronic applications. On a single molecular level, the molecular structures and their optical properties were correlated by computational methods. The combined results of morphology study, single crystal structure and two-dimensional wide-angle X-ray diffraction (2D-WAXD) indicated that the loss of the different molecular symmetry element affected the crystal dimensions. The microfibers of molecules 1 and 2 with their desirable crystal dimensions and surfaces were proved to be low-loss waveguide materials (0.02−0.05 dB/μm). Hence, we suggest that nonplanar aromatic core modified with proper side group may represent a promising approach to achieve crystalline optical waveguides. These structure−property investigations provide a deeper understanding for the structure and intermolecular interactions of such molecular aggregates.

2D Organic Photonics: An Asymmetric Optical Waveguide in Self‐Assembled Halogen‐Bonded Cocrystals

“…The PL intensity at the excited site along the body of the 2D cocrystals ( I body ) and at the emitting edge ( I tip ) were recorded, and the ratio I tip / I body shows a single‐exponential decay against propagation distance (Figure d), which indicates the active nature of the optical waveguide . The optical‐loss coefficient ( R ) was calculated by single‐exponential fitting I tip / I body = A exp(− RD ), where D is the distance between the excited site and the emitting edge . Accordingly, along the [100] direction of the 2D cocrystals, the optical‐loss coefficients of R Upward =0.0344 dB μm −1 and R Downward =0.0333 dB μm −1 at 525 nm suggest the symmetric optical waveguide, which is the same case as the previously‐reported optical waveguide devices .…”

Controlling the Structures and Photonic Properties of Organic Nanomaterials by Molecular Design

“…The distance dependent intensity of the nanowire, shown in Figure 3 c, indicates that the intensity of the out‐coupled light decays almost exponentially with the increase in propagation distance, which is a typical characteristic of active waveguides. The intensity at the excited site along the body of the nanowire ( I body ) and at the emitting tip ( I tip ) were recorded and the optical‐loss coefficient ( R ) was calculated by single‐exponential fitting I tip / I body = A exp(− R D ), where D is the distance between the excited site and the emitting tip 15. Accordingly, R =0.069 dB μm −1 at 450 nm, which is much lower than the value for other organic materials 16.…”

Lanthanide Metal–Organic Framework Microrods: Colored Optical Waveguides and Chiral Polarized Emission

“…[21] Thea verage R value was determined to be 0.025, 0.033, and 0.012 dB mm À1 for Tb-BTC, Eu@Tb-BTC and Eu-BTC,respectively,which are lower than those of organic materials [14b,c] and are close to inorganic nanowire and nanofiber waveguides. [21] Thea verage R value was determined to be 0.025, 0.033, and 0.012 dB mm À1 for Tb-BTC, Eu@Tb-BTC and Eu-BTC,respectively,which are lower than those of organic materials [14b,c] and are close to inorganic nanowire and nanofiber waveguides.…”