Optoelectronic Properties of Carbon‐Bound Boron Difluoride Hydrazone Dimers

Abstract

The creationo fd imericb oron difluoride complexes of chelating N-donor ligands is ap rovens trategy for the enhancement of the optoelectronic properties of fluorescent dyes. We report dimers based on the boron difluoride hydrazone (BODIHY) framework, whicho ffer uniquea nd sometimes unexpected substituent-dependent absorption, emission, and electrochemical properties. BODIHY dimers have low-energy absorption bands (l max = 421 to 479 nm, e = 17 200 to 39 900 m À1 cm À1 )t hat are red-shifted relative to monomeric analogues. THF solutionso ft hese dimers exhibit aggregation-induced emission upon additiono fw ater,w ith emissione nhancement factors ranging from 5t o1 8. Thin films of BODIHY dimers are weakly emissive as ar esult of the inner-filter effect,a ttributedt oi ntermolecular p-type interactions. BODIHY dimers are redox-active and display two one-electron oxidation and two one-electron reduction wavest hat strongly dependo nt he N-aryl substituents. These properties are rationalized using density-functional theoryc alculations and X-ray crystallography experiments. Results and Discussion Synthesis and characterizationHydrazone dimers 10 a-d were prepared by adapting al iterature procedure previously used for monomeric derivatives. [8f] This procedure involves condensationr eactionso ft he respective aryl hydrazines and 2,2'-pyridil (Scheme 1, Figures S1-S8).

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

“…, 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.…”

“…To explore the solid-state properties of BODIHYs 8 – 13 , we prepared thin films by spin-coating saturated CH 2 Cl 2 solutions of each BODIHY onto quartz slides and measured the corresponding absorption and emission spectra. The absorption and emission bands observed for the thin films were broadened, λ max and λ em values were red-shifted, and Φ em values ranged from 3 to 10%, which were in some cases enhanced relative to other BODIHYs with extended π-conjugation reported to date. , The onset of absorption was used to estimate E g Opt using the equation E g Opt = 1240/λ max onset (see Table below). Relative to BODIHY 5c , which has an E g Opt of 2.45 eV, there was a noticeable decrease in E g Opt for compounds 8 – 13 ranging from 2.02 to 2.25 eV, with compound 12 possessing the lowest E g Opt .…”

“…BODIHYs ( e.g. , 5 ) are BF 2 -containing heterocycles based on chelating pyridylhydrazone ligands, and these materials exhibit aggregation-induced emission and interesting redox chemistry. − We recently developed triphenylamine–BODIHY conjugates ( e.g. , 6 ) that exhibit dual emission, AIE, multiple redox waves, and charge-transfer characteristics .…”

Recent advances in the synthesis of luminescent tetra-coordinated boron compounds

“…232 Indole-pyridine, hydrazine, pyrrolyl-acylhydrazone, bipyridyl, pyridyl pyrrolide and semihemiporphyrazine based boron compounds were also studied for their tuneable photophysical properties. [237][238][239][240][241][242][243][244][245][246]…”

Access to tetracoordinate boron-doped polycyclic aromatic hydrocarbons with delayed fluorescence and aggregation-induced emission under mild conditions

“…In addition, the majority of previous attention has been paid to the tricoordinate boron units in PAHs, [55][56][57][58][59][60] tetracoordinate boron has been viewed more as a functional group instead of a dopant. [61][62][63][64][65][66] In fact, the coordination number of the boron atom shows noteworthy impact on the photophysical properties. Recently, effort to replace the three-coordinate boron of the BN unit with four-coordinate boron has been made (Scheme 1a).…”