Monodisperse Six‐Armed Starbursts based on Truxene‐Cored Multibranched Oligofluorenes: Design, Synthesis, and Stabilized Lasing Characteristics

Abstract

A series of monodisperse six‐armed conjugated starbursts (Tr1F, Tr2F, and Tr3F) containing a truxene core and multibranched oligofluorene bridges capped with diphenylamine (DPA) units has been designed, synthesized, and investigated as robust gain media for organic semiconductor lasers (OSLs). The influence of electron‐rich DPA end groups on their optoelectronic characteristics has been discussed at length. DPA cappers effectively raise HOMO levels of the starbursts, thus enhancing the hole injection and transport ability. Solution‐processed electroluminescence devices based on the resulting six‐armed starbursts exhibited efficient deep‐blue electroluminescence with clear reduced turn‐on voltages (3.2–3.5 V). Moreover, the resulting six‐armed molecules showed stabilized electroluminescence and amplified spontaneous emission with low thresholds (27.4–63.9 nJ pulse−1), high net gain coefficients (80.1–101.3 cm−1), and small optical loss (2.6–4.4 cm−1). Distributed feedback OSLs made from Tr3F exhibited a low lasing threshold of 0.31 kW cm−2 (at 465 nm). The results suggest that the construction of truxene‐centered six‐armed conjugated starbursts with the incorporation of DPA units can effectively enhance EL properties by precisely regulating the HOMO energy levels, and further optimizing their optical gain properties.

Lasing Operation under Long‐Pulse Excitation in Solution‐Processed Organic Gain Medium: Toward CW Lasing in Organic Semiconductors

“…OSLs, including laser operation under short excitation pulses, ranging from 100 femtoseconds (fs) to tens of nanoseconds (ns). [12][13][14][15][16][17][18][19] However, the operation of OSLs under long-pulse excitation of quasi-continuous wave (qCW) or CW regimes remains extremely challenging to achieve, even though it is widely believed as the key stepping stone toward electrically pumped lasers. [13,15,20] The main obstacle of long-pulse OSLs [i.e., millisecond (ms) range] is the indirect generation of triplet excitons (T 1 ) via intersystem crossing (ISC) of radiative singlet excitons.…”

Functionalized Truxene Scaffold: A Promising Advanced Organic Material for Digital Era

“…Lai and his teammates have synthesized six‐armed mono‐dispersed π‐conjugated truxene based multibranched oligofluorene ( 80 a‐c ) capped with diphenylamine (DPA) (Figure ). From the results, it was observed that the compounds capped with DPA starburst oligofluorene can boost its electrical activities by raising the HOMO levels, improving optical, and electroluminescence properties …”

Donor–Acceptor Type Pendant Conjugated Molecules Based on a Triazine Center with Depressed Intramolecular Charge Transfer Characteristics as Gain Media for Organic Semiconductor Lasers

“…[16,17] For example, several conjugated starburst molecules comprising truxene cores and oligofluorene bridges have been recently developed and demonstrated to be of improved hole injectionand transport ability andsuperior optical gain property with al ow threshold of 27.4 nJ pulse À1 ,b ecause of the incorporationo fd iphenylamine cappers. [18] This is an attractive strategy to enhance the hole and electron injection and trans-port at the same time with simultaneous incorporation of electron-donating and electron-withdrawing units into the molecular structures. However,s imultaneously integratinge lectrondonating and electron-withdrawing moieties into one molecule generally results in intramolecular charget ransfer (ICT) characteristics with broadened absorption,n arrowed band gaps, and nonlinear optical properties.…”

“…With this aim, it is an effective approach to incorporate electron‐donating units and/or electron‐withdrawing groups into the conjugated molecules to finely adjust the highest occupied molecular orbital (HOMO) and/or the lowest unoccupied molecular orbital (LUMO) levels, thus improving the carrier injection and transport properties . For example, several conjugated starburst molecules comprising truxene cores and oligofluorene bridges have been recently developed and demonstrated to be of improved hole injection and transport ability and superior optical gain property with a low threshold of 27.4 nJ pulse −1 , because of the incorporation of diphenylamine cappers . This is an attractive strategy to enhance the hole and electron injection and transport at the same time with simultaneous incorporation of electron‐donating and electron‐withdrawing units into the molecular structures.…”