Computationally Guided Molecular Design to Minimize the LE/CT Gap in D‐π‐A Fluorinated Triarylboranes for Efficient TADF via D and π‐Bridge Tuning

Abstract

In this combined experimental and theoretical study, a computational protocol is reported to predict the excited states in D‐π‐A compounds containing the B( F Xyl) 2 ( F Xyl = 2,6‐bis(trifluoromethyl)phenyl) acceptor group for the design of new thermally activated delayed fluorescence (TADF) emitters. To this end, the effect of different donor and π‐bridge moieties on the energy gaps between local and charge‐transfer singlet and triplet states is examined. To prove this computationally aided design concept, the D‐π‐B( F Xyl) 2 compounds 1 – 5 were synthesized and fully characterized. The photophysical properties of these compounds in various solvents, polymeric film, and in a frozen matrix were investigated in detail and show excellent agreement with the computationally obtained data. Furthermore, a simple structure–property relationship is presented on the basis of the molecular fragment orbitals of the donor and the π‐bridge, which minimize the relevant singlet–triplet gaps to achieve efficient TADF emitters.

Electronically Driven Regioselective Iridium‐Catalyzed C−H Borylation of Donor‐π‐Acceptor Chromophores Containing Triarylboron Acceptors

“…Compound 1 was synthesized analogously to our previously published methodology for donor‐π‐acceptor ( D ‐π‐A) compound 2 (Scheme ) . The brominated donor‐bridge moiety ( i and ii ) was lithiated using n BuLi in hexane.…”

“…We assume that the solvent coordinates to the fluoroborane, thereby reducing the reactivity towards nucleophiles. After purification via column chromatography, compounds 1 and 2 were isolated in excellent yields. The iridium‐catalyzed C−H borylation was conducted in hexane at room temperature with 1.5 to 1.7 equivalents of B 2 pin 2 and a catalyst loading of 1.5 to 3 mol % and 3 to 6 mol % ligand.…”

“…The relevance of boron in these systems is due to the empty p z ‐orbital on boron that can act as an electron acceptor (A) in conjugated systems. Based on this, potential applications of three‐coordinate boron have been investigated, such as for linear and non‐linear optics, bioimaging, sensors, frustrated Lewis pairs (FLPs), and organic light‐emitting diodes (OLEDs) . The drawback of the employment of three‐coordinate boron in conjugated systems, however, is their inherent reactivity towards nucleophiles, such as water, due to the empty p z ‐orbital.…”

“…This can be avoided by using bulky substituents or by fixing the boron center in a rigid scaffold . Only recently the use of ortho ‐trifluoromethylated aryls in triarylboranes has been established as a strategy to improve acceptor strength as well as stability . The improved acceptor strength can be attributed to the electron‐withdrawing nature of the trifluoromethyl groups, while the increase in stability is due to steric shielding of the boron center and its empty p z ‐orbital, as well as a direct interaction of the fluorine lone pairs with the empty p z ‐orbital on boron.…”

“…We have previously investigated donor‐π‐acceptor ( D ‐π‐A) systems with bis (2,6‐ bis (trifluoromethyl)phenyl)boryl ( B( F Xyl) 2 ) as the acceptor group . To fine tune the acceptor properties we wanted to look for a regioselective methodology to functionalize the acceptor in D ‐π‐A systems, exclusively.…”