RESUMEN
Materials exhibiting room temperature phosphorescence (RTP) are in high demand for signage, information encryption, sensing, and biological imaging. Due to weak spin-orbit coupling and other non-radiative processes that effectively quench the triplet excited states, RTP is sparsely observed in organic materials. Although the incorporation of a heavy atom through covalent or non-covalent modification circumvents these drawbacks, heavy-atom-containing materials are undesirable because of their deleterious side effects. Here, we designed and synthesized a new naphthalidenimine-boron complex as a coating material for the single crystals of 4,4'-dimethoxybenzophenone. The coated surface was observed to exhibit yellowish-green phosphorescence with ms lifetimes at ambient conditions through Förster resonance energy transfer (FRET). Importantly, the mechanical flexibility of the single crystals was observed to be retained after coating. The fluorescence-phosphorescence dual emission was utilised for colour-tunable optical waveguiding and anti-counterfeiting applications. As organic single crystals that can sustain mechanical deformations are emerging as the next-generation materials for electronic device fabrication, the flexible RTP organic crystals showing colour-tuneable optical waveguiding could be omnipotent in electronics.
RESUMEN
Tetra-coordinated organoboron (TCOB) compounds are promising candidates for developing high-performance optical devices due to their excellent optoelectronic performance. Fabricating TCOB-based nanomaterials of controlled and defined morphology through rapid and easy-to-execute protocols can significantly accelerate their practical utility in the aforesaid applications. Herein, we report water-induced self-assembly (WISA) to convert a polymorphic TCOB complex (HNBI-B, derived from a 2-(2'-hydroxy-naphthyl)-benzimidazole precursor) into two unique nanomorphologies viz. nanodiscoids (NDs) and fluorescent microtubes with hexagonal cross-sections (HMTs). Detailed electron microscopic investigations revealed that oriented assembly and fusion of the initially formed NDs yield the blue emissive HMTs (SSQY = 26.7%) that exhibited highly promising photophysical behaviour. For example, the HMTs outperformed all the crystal polymorphs of HNBI-B obtained from CHCl3, EtOAc and MeOH in emissivity and also exhibited superior waveguide behaviour, with a much lower optical loss coefficient α' = 1.692 dB mm-1 compared to the rod-shaped microcrystals of HNBI-B obtained from MeOH (α' = 1.853 dB mm-1). Thus, this work reports rapid access to high performance optical nanomaterials through WISA, opening new avenues for creating useful nanomaterial morphologies with superior optical performance.
