End Cap Effect on\nSolution-Processable Deep Blue Lasing\nMaterials with Low-Amplified Spontaneous Emission Thresholds

Organic lasers have attracted increasing attention owing\nto their\nsuperior characteristics such as lightweight, low-cost manufacturing,\nhigh mechanical flexibility, and high emission-wavelength tunability.\nRecent breakthroughs include electrically pumped organic laser diodes\nand an electrically driven organic laser, integrated with an organic\nlight-emitting diode pumping. However, the availability of efficient\ndeep blue organic laser chromophores remains limited. In this study,\nwe develop two novel rigid oligophenylenes, end-capped with carbazole\nand phenylcarbazole groups, to demonstrate exceptional optical and\namplified spontaneous emission (ASE) properties. These oligophenylenes\nare not only solution processable but also exhibit remarkably high\nsolution photoluminescence quantum yields (PLQYs) of 90% and high\nradiative rates of 1.35 × 10<sup>9</sup> s<sup>–1</sup> in the deep blue range. Our theoretical calculations confirm that\nthe carbazole and phenylcarbazole end groups play a pivotal role in\nenhancing the optical transitions of the oligophenylene laser chromophores,\nthereby elevating their emission oscillator strengths. Remarkably,\nthese materials demonstrate low solid-state ASE threshold values of\n1.0 and 1.5 μJ/cm<sup>2</sup> (at 431 and 418 nm, respectively).\nTo the best of our knowledge, these ASE thresholds represent the lowest\nreported at these specific ASE wavelengths in the literature, regardless\nof whether they are solution-processed or thermally evaporated films.\nFurthermore, they exhibit excellent thermal and photostability, low\ntriplet quantum yields, as well as negligible overlap of excited-state\nabsorption within the ASE emission region, making them excellent candidates\nfor a new class of deep blue materials for organic lasers. By integrating\ninsights from theoretical calculations and experimental validation,\nour study provides a comprehensive understanding of the design principles\nbehind these high-performing organic laser chromophores, paving the\nway for the development of advanced organic lasers with enhanced performance\ncharacteristics.