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

Abstract

Molecular materials with π-conjugated donor–acceptor (D–A) and acceptor–donor–acceptor (A–D–A) electronic structures have received significant attention due to their usage in organic photovoltaic materials, in organic light-emitting diodes, and as biological imaging agents. Boron-containing molecular materials have been explored as electron-accepting units in compounds with D–A and A–D–A properties as they often exhibit unique and tunable optoelectronic and redox properties. Here, we utilize Stille cross-coupling chemistry to prepare a series of compounds with boron difluoride hydrazones (BODIHYs) as acceptors and benzene, thiophene, or 9,9-dihexylfluorene as donors. BODIHYs with D–A and A–D–A properties exhibited multiple reversible redox waves, solid-state emission with photoluminescence quantum yields up to 10%, and aggregation-induced emission (AIE). Optical band gaps (or highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps) determined for these compounds (2.02–2.25 eV) agree well with those determined from cyclic voltammetry experiments (2.05–2.42 eV). The optoelectronic properties described herein are rationalized with density functional theory calculations that support the interpretation of the experimental findings. This work provides a foundation of understanding that will allow for the consideration of D–A and A–D–A BODIHYs to be incorporated into applications ( e.g. , organic electronics) where fine-tuning of band gaps is required.

Boron difluoride hydrazone (BODIHY) complexes: A new class of fluorescent molecular rotors

“…More recently, [ 62 ] Cappello and coworkers built upon their previous D–A and A–D–A systems by altering the nature of the donor to either a benzene, thiophene, or 9,9‐dihexylfluorene unit (Figure 11). These systems were synthesized following previously reported procedures.…”

“…Dyes 41-43 were synthesized in moderate yields (46 to 55%) following established literature procedures. [52,62] The photophysical studies reveal λ max values ranging from 394 to 400 nm and λ em values ranging from 500 to 532 nm. BODIHY 43 has blueshifted λ max and λ em bands in solution relative to 41 and 42, which may be attributed to the presence of the electronwithdrawing σ-spacer.…”

Boron Complexes of Tridentate Acyl Pyridylhydrazones

“…BODIHY chemistry was pioneered by the Aprahamian group [13][14][15][16][17][18][19] and has also been studied by the Gilroy group and others. [20][21][22][23][24][25][26][27][28] In search of novel structures and properties, further iterations of BODIHY syntheses have involved modifications to the peripheral structure. [16] This includes variants functionalized with electron-withdrawing and donating groups, [13] dimerization through different sites on the ligand, [22][23][24] and the incorporation of a benzothiazole group in place of pyridine.…”

Design, synthesis and functionalization of BODIPY dyes: applications in dye-sensitized solar cells (DSSCs) and photodynamic therapy (PDT)

“…The development of novel multi-modular conjugated D-A chromophores has attracted interest from the scientific community due to their wide range of applications in organic solar cells, organic photovoltaics, thermally activated delayed fluorescence (TADF), non-linear optics (NLOs) as well as in biological studies. [1][2][3][4][5][6][7][8] Such D-A-based chromophores, which exhibit high thermal and photochemical stability, broad absorption in the UV-vis range and narrow bandgaps, are potential candidates for optoelectronic applications. 9 The D-A strategy has been used for the development of NIR-absorbing/emitting materials with a narrow HOMO-LUMO gap.…”