Unique 2D Face Topologies in Naphthyl‐Appended Naphtho[k]fluoranthene‐Based 3D Crystals for Optical Waveguide

Abstract

Molecular crystals exhibiting optical waveguiding are strongly dependent on total internal reflection, molecular stacking arrangements, spatial distributions of transition dipole moments, and topologies. Fluoranthene derivatives are popular fluorescent dyes that have not yet been engineered into crystalline optical materials. Here, a naphthyl‐appended naphtho[k]fluoranthene that exhibits efficient fluorescence in solution and in the solid state is newly synthesized through a one‐pot Pd‐catalyzed reaction of 1,8‐dibromonapthalene. It selectively gives two crystal topologies derived from direction‐specific crystal growth. Using spatially resolved photoluminescence analyses, the direction‐oriented light that propagates along these topologies (each face of the crystal) is investigated. There are different optical‐loss coefficients along the various directions on each face. Therefore, face‐specific waveguiding depends on molecular arrangements. Anisotropic waveguiding in each face is observed. Overall, these results suggest potential applications of fluoranthene crystals and their topological 2D planes as optical waveguides and integrated optical circuits.

Non‐Covalent Supramolecular 1D Alternating Copolymer in Crystal toward 2D Anisotropic Photon Transport

“…Such a cocrystal is expected to have anisotropic OWG properties. [26,28,29] Microscopic observations and PL spectral measurements of the cocrystal were performed using a focused laser beam (λ ex = 405 nm) as an excitation source (Figure S11). When a 2Dplatelet-shaped cocrystal was irradiated by the focused laser beam, we observed that light was guided toward the edge of the crystal.…”

“…A large difference in the loss coefficient indicated extremely anisotropic OWG properties. Notably, the anisotropic waveguiding ability and α S /α L values of a 2D platelet crystalbased anisotropic waveguide have been reported to be < 3.9; [26][27][28][29] thus, this cocrystal with a 1D-ordered supramolecular of alternating copolymer was more than an order of magnitude greater, at 41. A 1D copolymer of a highly fluorescent molecule 1 with 2 formed an angle-controlled supramolecular synthons aligned horizontally with the 2D crystal surface.…”

“…[21][22][23][24][25] Moreover, control over the anisotropic transport of photons has attracted much attention for the development of optical logic gates composed of a single component. [26][27][28][29][30] Anisotropic transmission behavior of photons, that is, different optical waveguiding in different directions within molecular crystals, has been demonstrated owing to control over anisotropic molecular packing and electronic coupling interactions. However, the anisotropy of photon propagation in organic molecular crystals is not so drastic.…”

“…This effect has been attributed to inclined orientations of TDMs in a twodimensional (2D) crystal. [26][27][28][29][30][31][32] The loss coefficients for photon transport (optical waveguiding) in the long and short-axis directions of a crystal are denoted by α L and α S , respectively. For π-conjugated molecules, the relationship between α L and α S is ordinally described as α S < α L because π-electrons have strong intermolecular interactions in the long crystal axis direction.…”

Flexible and Red-Emissive Organic Single-Crystal Microresonator for Efficient Active Waveguides

“…Organic molecular crystals are generally brittle; thus, crystal photonic components, such as optical waveguides (OWGs), resonators, and lasers, have been widely developed as rigid materials. − However, organic molecular crystals with mechanical flexibility based on elasticity or plasticity have recently emerged and are gaining interest − as irreplaceable OWG platforms. − For practical applications, heterostructures composed of organic microcrystals are constructed, − and optical logic gates have been demonstrated. − Highly aligned organic molecular crystals have been also constructed, even in solution. − Among the various organic molecular crystals, those with a needlelike morphology are ideal candidates to transport photons unidirectionally. In organic π-conjugated molecules, exciton–polaritons (EPs) can be formed as a result of strong coupling between excitons and resonator photons. − Because of the large exciton binding energies for organic molecules, EPs are formed, even at room temperature.…”