Design and Synthesis of Monodisperse Macromolecular Starbursts Based on a Triazine Center with Multibranched Oligofluorenes as Efficient Gain Media for Organic Lasers

A set of monodisperse macromolecular starbursts which are composed of triazine center substituted by heterogeneous carbazole and diphenylamine units with multibranched oligofluorenes (TF1 and TF2) have been designed, synthesized, and explored as gain media for organic lasers. The thermal, morphological, photophysical, and electrochemical properties and optical gain characteristics of the resulting starbursts have been investigated in comparison with those of their linear counterparts (2FCz and 4FCz) to shed light on better understanding the structure-property relationships. The results manifest that the resulting starburst architectures based on a triazine center with multibranched oligofluorenes are beneficial for depressing the crystallization tendency, leading to enhanced amorphous morphologies, excellent thermal stabilities, and favorable facile solution processability. The novel heterogeneous donor-acceptor core structure based on triazine center plays a key role to dominate the electronic properties of the resulting multibranched starbursts and endows the molecules with low-lying LUMO energy levels. Promising amplified spontaneous emission (ASE) characteristics are recorded for the multibranched starbursts, in which TF1 and TF2 exhibit rather low ASE threshold (E_th^ASE) of 4.3 and 10.3 μJ/cm², respectively. Remarkably, TF1 and TF2 manifest enhanced ASE stability with no obvious spectral variations (within 2 nm for TF1 and 1 nm for TF2) and almost unchanged E_th^ASE upon increasing the annealing temperature even up to 200 °C in air. In contrast, their linear counterparts 2FCz and 4FCz showed distinct E_th^ASE variations with increasing the annealing temperature above 100 °C. The results suggest that the novel molecular design is beneficial for enhancing the thermal and optical stabilities as well as fine modulating the electrical properties, rendering the resulting multibranched triazine-centered starbursts advantageous as efficient gain media for electrically pumped organic lasers.