Synthesis, computational, and spectroscopic analysis of tunable highly fluorescent BN-1,2-azaborine derivatives containing the N-BOH moiety

Abstract

Nine new polycyclic aromatic BN-1,2-azaborine analogues containing the N-BOH moiety were synthesized using a convenient two-step, one-pot procedure. Characterization of the prepared compounds show the luminescence wavelength and the quantum yields of the azaborines were tunable by controlling the power and location of the donor and acceptor substituents on the chromophore. UV-visible spectroscopy and density functional theory (DFT) computations revealed that the addition of electron-donating moieties to the isoindolinone hemisphere raised the energy of the HOMO, resulting in the reduction of the HOMO-LUMO gap. The addition of an electron-accepting moiety to the isoindolinone hemisphere and an electron-donating group to the boronic acid hemisphere decreased the HOMO-LUMO gap considerably, leading to emission properties from partial intramolecular charge transfer (ICT) states. The combined effect of an acceptor on the isoindolinone side and a donor on the boronic acid side (strong acceptor-π-donor) gave the most red-shifted absorption. The polycyclic aromatic BN-1,2-azaborines emitted strong fluorescence in solution and in the solid-state with the largest red-shifted emission at 640 nm and a Stokes shift of Δλ = 218 nm, or Δν = 8070 cm.

Predicting Absorption and Emission Maxima of Polycyclic Aromatic Azaborines: Reliable Transition Energies and Character

“…Unfortunately, despite the generally excellent correlation for the rest of the data, EOM-CCSD does not predict λ em for the nitro compounds that are in agreement with the experimental data. Recalling that the data in Figure 3 represents "gas-phase" computations and the predicted character from B3LYP and the experiment is an ICT transition, 11 this observation is not necessarily shocking. However, across the results for each range-corrected functional and EOM-CCSD, the λ em of the nitro compounds is consistently further away from the trend line compared to standard hybrid functionals.…”

“…4,6−10 Additionally, several luminescent azaborines have been reported that are relatively small, with some previously reported compounds having only three fused rings. 5,11 Due to their potential applications and their relative structural simplicity, these compounds are prime candidates for computational design and screening if a viable methodology can be determined. Based on the data in our previous publication, 11 a reasonable correlation to the experiment could be found for the predicted maxima of nearly all compounds in Figure 1 using TD-B3LYP (with a double-zeta quality basis set) single-point computations (absorption, λ max ) or optimizations (emission, λ em ) on single molecules in isolation.…”

“…5,11 Due to their potential applications and their relative structural simplicity, these compounds are prime candidates for computational design and screening if a viable methodology can be determined. Based on the data in our previous publication, 11 a reasonable correlation to the experiment could be found for the predicted maxima of nearly all compounds in Figure 1 using TD-B3LYP (with a double-zeta quality basis set) single-point computations (absorption, λ max ) or optimizations (emission, λ em ) on single molecules in isolation. However, the computed data for the nitro compounds gave a poor correlation to the experimental results for λ em .…”

“…Replacing one of the C–C groups in an aromatic benzenoid with a B–N group results in an aromatic azaborine compound. Polycyclic aromatic azaborines have been extensively studied due to their intense absorption, high quantum yields, and photostability. − Materials containing these chromo-/luminophores have potential applications in devices such as organic field effect transistors (OFETs) and organic light-emitting diodes (OLEDs). ,− Additionally, several luminescent azaborines have been reported that are relatively small, with some previously reported compounds having only three fused rings. , Due to their potential applications and their relative structural simplicity, these compounds are prime candidates for computational design and screening if a viable methodology can be determined. Based on the data in our previous publication, a reasonable correlation to the experiment could be found for the predicted maxima of nearly all compounds in Figure using TD-B3LYP (with a double-zeta quality basis set) single-point computations (absorption, λ max ) or optimizations (emission, λ em ) on single molecules in isolation.…”

Six-Membered Rings With Two or More Heteroatoms With at Least One Boron

“…For example, the reaction of 6-bromoisoindolinone with 2-formylphenylboronic acid using DBU in ethanol gave azaborine 117 in 84% yield (Scheme 50). 144 The synthesis of 10b-aza-10c-borapyrene 118 has been performed via the combination of 2,6-diethynylpyridine with a cyclic borane using a microwave reactor and carefully controlling reaction conditions (Scheme 51). 29,145 The polycyclic borazine 120 containing alternating BR and NR units has been prepared from diborate(4) anion, derived from the diborane 119, and two equivalents of B 2 Cl 2 (NMe 2 ) 2 (Scheme 52).…”