Dual Emission, Aggregation, and Redox Properties of Boron Difluoride Hydrazones Functionalized with Triphenylamines

Abstract

π‐Conjugated molecular materials often exhibit interesting photoluminescence, redox, and optoelectronic properties that grant them utility as light‐harvesting materials in solar cells, as the emissive component of organic light‐emitting diodes, and as fluorescence sensors. Preparing dye conjugates by appending multiple dyes together to generate π‐conjugated molecules is a common strategy to enhance the properties of these materials as it often imparts traits that cannot be achieved by the building blocks independently. Herein, we report molecular materials that incorporate boron difluoride hydrazone (BODIHY) and triphenylamine (TPA) units that exhibit charge‐transfer character, dual‐emission, and aggregation‐induced emission. The title compounds have low‐energy absorption bands (λabs=455–493 nm) that are red‐shifted relative to BODIHYs with smaller π‐systems and exhibit dual‐emission in the solution, solid, and aggregate states. TPA–BODIHY (donor‐acceptor) conjugates show multiple reversible redox events and, in combination, the data presented herein indicate that there is electronic communication throughout the donor‐acceptor and acceptor‐donor‐acceptor π‐systems. These results are rationalized with the use of computational chemistry and solid‐state structural analysis. This study provides new opportunities for the design of molecular materials that are comprised of redox‐active photoluminescent dyes, including BODIHY, and their potential applications.

Tuning the Properties of Donor–Acceptor and Acceptor–Donor–Acceptor Boron Difluoride Hydrazones via Extended π-Conjugation

“…They were 14 for 8 , 13 for 9 , 12 for 10 , 4 for 12 , and 9 for 13 . The observed red shift in λ em with increasing f w and the blue-shifted and enhanced emission observed for thin films containing PMMA doped with 1% BODIHY are consistent with trends observed for related BODIHYs 61 − 63 and imply that RIM is a plausible contributor to the AIE behavior observed.…”

“… 60 Our approach began by preparing Br–BODIHY 7 according to a literature procedure. 61 Benzene (BE), thiophene (TH), and 9,9-dihexylfluorene (FL) were chosen as donors due to the commercial availability and/or synthetic accessibility of the relevant synthons ( Figures S1 and S2 ) and the variation of the size of the corresponding π-electron systems. BODIHY 7 was combined with monosubstituted organotin reagents of BE, TH, or FL using 5 mol % Pd 2 (dba) 3 /10 mol % P( o -tolyl) 3 in toluene and heated to 170 °C with stirring for 15 min in a sealed tube (pressure 3.2–4.3 bar) to yield BODIHYs 8 – 10 ( Figures S3–S8 ).…”

“…, toluene → THF), supporting the hypothesis that the relevant electronic transitions observed for BODIHYs 11 – 13 may have charge-transfer character. Like other BODIHYs, 61 − 63 , 67 , 68 compounds 8–13 exhibited weak solution-state emission due to nonradiative relaxation pathways arising from the rotation and/or vibration of the aryl substituents appended to the BODIHY heterocycle. The wavelength of maximum emission (λ em ) for BODIHY 5c in THF is 547 nm and λ em for 8 – 13 were red-shifted by Δλ em = 2 nm for 8 , Δλ em = 29 nm for 9 , Δλ em = 57 nm for 10 , Δλ em = 48 nm for 11 , Δλ em = 96 nm for 12 , and Δλ em = 45 nm for 13 , with Φ em < 1% for all compounds.…”

“…Reagents were purchased from Alfa Aesar, Fisher Scientific, Oakwood Chemicals, Sigma-Aldrich, or TCI America and used as received. 2-Bromo-9,9-dihexylfluorene, 77 2,7-bis(trimethylstannyl)-9,9-dihexylfluorene, 78 and BODIHY 7 ( 61 ) were prepared according to procedures reported in the literature. Stille cross-coupling reactions were conducted in an Anton Paar Monowave 50 reactor.…”

“…, 6 ) that exhibit dual emission, AIE, multiple redox waves, and charge-transfer characteristics. 61 Inspired by the traits associated with these BODIHY-bearing strong triarylamine donors, we were interested in utilizing BODIHYs as electron acceptors and altering the nature of the donor in D–A and A–D–A architectures. Herein, we present a systematic approach to investigating structure–property relationships for BODIHYs linked to several donors in D–A and A–D–A molecular frameworks and present their optoelectronic, AIE, and redox properties.…”