Highly Deep‐Blue Luminescent Twisted Diphenylamino Terphenyl Emitters by Bromine‐Lithium Exchange Borylation‐Suzuki Sequence

Abstract

Four novel intensively blue luminescent chromophores were readily synthesized by bromine-lithium exchange borylation-Suzuki (BLEBS) sequence in moderate to good yields. Their electronic properties were studied by absorption and emission spectroscopy and quantum chemical calculations revealing deep-blue emission in solution as well as in the solid state and upon embedding into a PMMA (polymethylmethacrylate) matrix with small FWHM (full width at half maximum) values and CIE y values smaller than 0.1. Moreover, high photoluminescence quantum yields (PLQY), partially close to unity, are found.

Highly Luminescent Blue Emitter with Balanced Hybridized Locally and Charge‐Transfer Excited‐States Emission

“…From the slope of the fit using the Lippert-Mataga equation (see Equation S1) Δμ � 21 D was obtained, where an Onsager radius of 5.60 Å was estimated from the optimized geometry and crystal structural data. [14] Low-temperature measurements at 110 K in toluene/ cyclohexane allow for estimating a ΔE S 1 À T 1 value of 0.82 eV (see Figure S12) in good agreement with quantum chemical calculations (0.76 eV; see below). Therefore, we conclude that reverse intersystem crossing (rISC) of the T 1 population is highly unlikely, [20] and 3 can be classified as typical singlet emitter.…”

“…Recently, we showed that functional donor‐acceptor TADF chromophores are efficiently accessed by one‐pot methodologies [13] . This approach was also successfully applied to study effects of extended π‐conjugation with steric hindrance in a series of four terphenyl based blue emitters [14] . Here, we selected the most intensely emissive molecule 3 with PLQYs of 0.96 and higher in solution (toluene, dichloromethane), in the solid state and in a PMMA film.…”

“…the luminescence decays and demonstrating a single emissive species, [14] is untypical for pure CT transitions, typically occurring around 10 6 s À 1 , and evidence for some LE contribution to the S 1 state. Fluorescence lifetimes between 1-4 ns fall into a typical range for organic chromophores.…”

“…[13] This approach was also successfully applied to study effects of extended π-conjugation with steric hindrance in a series of four terphenyl based blue emitters. [14] Here, we selected the most intensely emissive molecule 3 with PLQYs of 0.96 and higher in solution (toluene, dichloromethane), in the solid state and in a PMMA film. The synthesis takes advantage of practical one-pot bromine-lithium exchange borylation-Suzuki (BLEBS) sequence [15] starting from 4-bromo-3methyl-N,N-diphenylaniline (1) as the donor part and 4'-bromo-[1,1'-biphenyl]-4-carbonitrile (2) as acceptor coupling partner (Scheme 1).…”

“…Δf [b] Stokes shift [c] [cm À 1 ] FWHM [d] [14] 402 450 (0.98) 8.16 1.20 • 10 8 2.45 • 10 6 -2650 46 (0.28) 0.150, 0.088 in 1 wt % PMMA film [14] 362 430 (0.96) 2.…”