Dendron-Functionalized Macromolecules:  Enhancing Core Luminescence and Tuning Carrier Injection

Abstract

A novel series of naphthalimide dendrimers has been synthesized based on a convergent and divergent combined approach. The dendrimers consist of naphthalimide-based cores, Fre ´chet-type poly(aryl ether) dendrons, and carbazole (CZ) or oxadiazole (OXZ) peripheral groups. The higher generation dendrimer has site-isolation effect, or the dilution effect of the dendrons. This configuration would reduce the aggregating extent or possibility of the core unit, thus resulting in a relatively small red-shift of absorption and fluorescent spectra when they form a solid film for the applications. Studies of steadystate fluorescence properties of the dendrimers show that excitation of the terminal chromophores results mainly in the core emission alone, as the donor emission is seriously quenched due to its effective Fo ¨rster intramolecular energy transfer to the core. The dendrimers show enhanced luminescence properties of the core, and the enhanced luminescent efficiency is dependent on the generation number of the dendrimers. Time-resolved luminescent measurements further supported the conclusion that the contribution tendency for each peripheral donor is decreased with the increasing of the generation number, especially for the third generation. The dendron-incorporated carbazole unit can decrease the HOMO orbital energy by 0.4 eV, thus facilitating the hole-injection in electroluminescent (EL) devices. The preliminary EL results with a single-layer architecture made with the dendrimers by means of the spincoating technique demonstrate that these dendrimers could be utilized as promising active nondoping emitters.

Synthesis of Carrier‐Transporting Dendrimers with Perylenebis(dicarboximide)s as a Luminescent Core

“…The dendritic architecture can also be used to improve the solubility of luminescent chromophores to form uniform films by the spin-coating technique, thus overcoming the high cost of the vacuum-deposition process. In spite of the impressive control of solubility and amorphous form, [23,24] the design of modulating charge-carrier-transporting dendrimers for OLED applications is so far rare.…”

“…[25] In line with our ongoing efforts on studying multi-chromophoric emitters containing a carrier-transporting unit as the EL active layer for optimized device performance, [23,26] we designed a series of novel dendrimers with different generations by a convergent synthetic approach on the basis of the following considerations: (1) dendron functionalization, (2) incorporating CZ or OXZ units to tune carrier injection, (3) tuning or improving solubility, functionality, and glass-transition temperature (T g ) with well-defined dendrons, and (4) avoiding core luminescence quenching with the help of high dendron site-isolation to enhance the core luminescence.…”

“…Finally, the tosylation of compound 25 was attempted as this method has proved effective in our synthesis of dendrimers based on 1,8-naphthalenedicarboximide. [23] Unfortunately, all these reactions failed to afford the desired compound, probably because of the poor solubility of compound 37 in DMF.…”

“…[18][19][20] Recently, a class of rigid polyphenylene dendrimers based on the chromophore of perylenebis(dicarboximide)s have been studied by Müllen et al Those dendrimers show good solubility and film-forming properties, and display strong redorange photoluminescence with decreasing chromophore interactions, although the efficiencies of devices fabricated with these materials were still low due to poor charge-transport through the dendritic shell. [21,22] We have previously reported a class of naphthalenedicarboximide dendrimers exhibiting specific light-harvesting and carrier injection-tuning properties, [23] and herein we extend this work to present the synthesis of three series of flexible dendron-functionalized dendrimers as red-lightemitting materials by a convergent approach: (1) carbazole (CZ) or oxadiazole (OXZ) terminated imide-type dendrimers, (2) cascade energy-transferring imide-type dendrimers, and (3) CZ-terminated bay-type dendrimers (shown in Schemes 1, 2, and 3, respectively). They are characteristic of the luminescent core of perylenebis(dicarboximide)s with specific functional groups (CZ or OXZ) at the periphery constructed by flexible Fréchet-type poly(aryl ether) dendrons.…”

Electroluminescent Properties of an Electrochemically Cross‐Linkable Carbazole Peripheral Poly(Benzyl Ether) Dendrimer

“…[3] Recently, energy transfer (Fçrster or Dexter) and charge trapping on metal complexes of dyes in PVK and PVK:PBD blend [4][5][6][7][8] systems have been studied to obtain high efficiency device performance and electroluminescence mechanism. In addition, copolymers [9,10] or dendrimers [11] should offer the opportunity to alter charge transport properties in a controlled fashion and facilitate understanding of charge trapping effects in these materials. Trapped charge carriers can be recombined at specific sites or interfaces and generate excitons from various excited-state complexes, such as excimer, exciplex, and electroplex states.…”