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Polymorph-Dependent Emission in Cyano Group-Substituted Thiophene/Phenylene Co-Oligomer Crystals

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide This paper presents the preparation and optical characterization of two crystal polymorphs (light-blue- and green-emitting crystals) of 2,5-bis(4′-cyanobiphenyl-4-yl)thiophene (BP1T-CN), a cyano-substituted thiophene/phenylene co-oligomer (TPCO) that has not been previously reported. Light-blue-emitting triclinic and green-emitting monoclinic crystals were fabricated via physical vapor transport (PVT) and solution-growth methods, respectively. Structural analysis using X-ray diffraction (XRD) revealed that the light-blue- and green-emitting polymorphs correspond to triclinic and monoclinic forms, respectively. In the light-blue-emitting crystals, π–π interactions are weakened due to the small overlap of molecular π planes. Meanwhile, in the green-emitting crystals, strong π–π interactions arose because the molecules stack parallel to the a -axis (the shortest axis length), leading to a red shift of 8 nm in the optical spectra due to energy stabilization. Both polymorphs demonstrated high photoluminescence quantum yields (PLQYs) of 58% (light blue) and 60% (green) and exhibited Fabry–Pérot lasing behavior under optical excitation with thresholds of 67 and 75 μJ/cm 2, respectively. The suitability of both polymorphs as laser media, together with their nearly parallel orientation with respect to the crystal basal plane of the bent-shaped molecular structures induced by Coulomb interactions between cyano groups, opens up further possibilities for applications such as exciton–photon strong coupling, vertical-cavity surface-emitting lasers (VCSELs), and high-performance charge injection and transport in devices, including organic field-effect transistors and organic thin-film solar cells.

Source: ACS Omega

DOI: 10.1021/acsomega.5c09709

Authors: Nanang Adrianto, Hitoshi Mizuno, Andi Marwanti Panre, Tomomi Jinjyo, Hiroyuki Katsuki

Institutions: Nara Institute of Science and Technology, Toyama Prefectural University

Language: English

Topic: Luminescence and Fluorescent Materials

Subfield: Materials Chemistry

Field: Materials Science

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $1,935

Funders: Ministry of Education, Culture, Sports, Science and Technology, Japan Society for the Promotion of Science