New 4,4′-Bis(9-carbazolyl)–Biphenyl Derivatives with Locked Carbazole–Biphenyl Junctions: High-Triplet State Energy Materials

Abstract

We synthesized a series of CBP derivatives, using methyl groups as spatially demanding groups, locking the angle between the carbazole subunit and the biphenyl backbone as potential matrix material for blue organic light emitting diodes (OLEDs). The locked rotation was achieved by four methyl groups either in the 1,8-positions of the carbazole subunit (1) or in the 3,5,3',5'-positions of the biphenyl subunit (2) and the fixed spatial arrangement was confirmed by x-ray analysis. The physical properties of CBP derivatives based on the parent structure 2 were further tailored by electron withdrawing CF 3groups in 3,6-or 2,7-positions of the carbazole subunits (3 and 4) or alternatively by electron donating CH 3 O-groups in the 2,7-positions (5) of the same building blocks. Increased triplet energies (E T ) compared to the parent compound CBP were found for all synthesized CBP derivatives 1-5. Enhanced glass transition temperatures ranging between 129°C to 205°C further corroborate the application potential of these derivatives for matrix material in blue emitting OLEDs.

High Efficiency Deep‐Blue Phosphorescent Organic Light‐Emitting Diodes with CIE x, y (≤ 0.15) and Low Efficiency Roll‐Off by Employing a High Triplet Energy Bipolar Host Material

“…We also measured the T g of new m‐ CBPPO host, which was above 100 °C. The obtained value was relatively higher when compared to the T g of conventional host materials mCP, 4,4′‐bis(9‐carbazolyl)‐biphenyl and 4,4′‐bis(9‐carbazolyl)‐2,2′‐dimethylbiphenyl (55, 62, and 94 °C, respectively) . The systematic design strategy of m‐ CBPPO allowed us to achieve a high T d and T g .…”

Addressing Charge‐Transfer and Locally‐Excited States in a Twisted Biphenyl Push‐Pull Chromophore

“…Controlling the coupling of the charge-transfer process with nuclear degrees of freedom helps to single out the effects of solvation. Various "push-push", "pull-pull" and "push-pull" systems have been reported in the literature based on functionalized biphenyl cores, [26,27] with applications in two-photon absorption, [30][31][32] sensing, [33] lightemitting devices, [34] solar energy conversion. Optical spectra of model systems for electron transfer are often characterized by a subtle interplay between locally-excited (LE) and charge-transfer (CT) states, strongly affected by the solvent.…”

“…The interaction with the solvent plays a strong role in electron-transfer processes since charge-transfer states are characterized by large permanent dipole moments and hence strongly interact with polar solvents. [29,34,35] The extent of π overlap in the two benzene rings affects the extent of electronic delocalization over the entire π system. Many of these systems display dual fluorescence in polar solvents [12][13][14][15]28,29] and show transient optical behavior strongly dependent on the solvent itself.…”

“…[17][18][19]23,26] In this paper, we investigate a push-pull substituted biphenyl compound (hereafter TBP) where the electron-donor and the electron-acceptor groups are connected to the biphenyl central core via extended π-conjugated bridges favoring long-distance electron transfer. Various "push-push", "pull-pull" and "push-pull" systems have been reported in the literature based on functionalized biphenyl cores, [26,27] with applications in two-photon absorption, [30][31][32] sensing, [33] lightemitting devices, [34] solar energy conversion. [29,34,35] The extent of π overlap in the two benzene rings affects the extent of electronic delocalization over the entire π system.…”

“…Various "push-push", "pull-pull" and "push-pull" systems have been reported in the literature based on functionalized biphenyl cores, [26,27] with applications in two-photon absorption, [30][31][32] sensing, [33] lightemitting devices, [34] solar energy conversion. [29,34,35] The extent of π overlap in the two benzene rings affects the extent of electronic delocalization over the entire π system. This varies with the torsional angle between the planes of the two phenyl rings.…”