Persistent luminescence is a fascinating phenomenon with exceptional applications. However, the development of organic materials capable of persistent luminescence, such as organic persistent room-temperature phosphorescence, lags behind for their normally low efficiency. Moreover, enhancing the phosphorescence efficiency of organic luminophores often results in short lifetime, which sets an irreconcilable obstacle. Here we report a strategy to boost the efficiency of phosphorescence by intramolecular triplet-triplet energy transfer. Incorpotation of (bromo)dibenzofuran or (bromo)dibenzothiophene to carbazole has boosted the intersystem crossing and provided an intramolecular triplet-state bridge to offer a near quantitative exothermic triplet–triplet energy transfer to repopulate the lowest triplet-state of carbazole. All these factors work together to contribute the efficient phosphorescence. The generation and transfer of triplet excitons within a single molecule is revealed by low-temperature spectra, energy level and lifetime investigations. The strategy developed here will enable the development of efficient phosphorescent materials for potential high-tech applications.
drawbacks. In addition to the higher material costs of these rare-earth metals, many inorganic LPLs require harsh synthetic procedures, [11] further increasing research costs. Organic LPL (OLPL) materials, [12][13][14][15][16] offer the promise of a multitude of benefits: easier synthesis, easier modification for targeted functionality, and easier processing. However, the development of OLPL materials has encountered many obstacles. To access long lived states in organic compounds, there have been many designs to exploit the excited triplet state. Though access to and from the triplet state is a forbidden process and once thought to be too inefficient for effective use at room temperature, [17] recent advances have vastly increased intersystem crossing efficiency by enhancing spin-orbit coupling (SOC) with the use of heteroatoms, [18,19] the carbonyl functional group, [20][21][22] heavy atom effects, [23][24][25][26][27] and multimer-enhanced intersystem crossing. [28][29][30][31][32] Equally important is protecting the long-lived triplet after its generation, due to the fact that they are particularly sensitive to molecular vibrational quenching and atmospheric oxygen. In this regard, recent works have accomplished this through the use of crystals, [33,34] metal-organic frameworks, [35] H-aggregation, [36] and others. [30,32,37] Although there have been many achievements in generating organic room-temperature Because of their innate ability to store and then release energy, longpersistent luminescence (LPL) materials have garnered strong research interest in a wide range of multidisciplinary fields, such as biomedical sciences, theranostics, and photonic devices. Although many inorganic LPL systems with afterglow durations of up to hours and days have been reported, organic systems have had difficulties reaching similar timescales. In this work, a design principle based on the successes of inorganic systems to produce an organic LPL (OLPL) system through the use of a strong organic electron trap is proposed. The resulting system generates detectable afterglow for up to 7 h, significantly longer than any other reported OLPL system. The design strategy demonstrates an easy methodology to develop organic long-persistent phosphors, opening the door to new OLPL materials.Long-persistent luminescent [1,2] (LPL) materials have demonstrated great potential and performance in multiple areas, such as life sciences, [3] the biomedical field, [2,4] and photo voltaics, [5] as they offer fascinating possibilities for their ability to store and slowly release excited state energy. For example in biomedical applications, LPL materials can be used postexcitation, overcoming any issue of autofluorescence. [6][7][8] Currently, the most successful LPL materials make use of transition and rare-earth metal ions. [9,10] Although the metals grant exceptionally long afterglows that range from minutes to hours, with some systems lasting days and weeks, [11] they are not without their inherentThe ORCID identification number(s) for the aut...
Long-persistent luminescence (LPL), also known as afterglow, is a phenomenon in which the material shows long-lasting luminescence after the cessation of the excitation source. The research of LPL continues to attract much interest due to its fundamental nature and its potential in the development of the next generation of functional materials. However, most of the current LPL materials are multicomponent inorganic systems obtained after harsh synthetic procedures and often use rare-earth metals. Recently, metal free organic long-persistent luminescence (OLPL) has gained much interest because it can bypass many of the disadvantages of inorganic systems. To date, the most successful method to generate OLPL systems is to access charge-separated states through binary donor–acceptor exciplex systems. However, it has been reported that the ratios of the binary systems affect OLPL properties, complicating the reproducibility and large-scale production of OLPL materials. Simpler OLPL systems can overcome these issues for the benefit of the development and adoption of OLPL systems. Here, we report on the rational design and synthesis of a single-component OLPL system with detectable afterglow for at least 12 min under ambient conditions. This work exemplifies an easy design principle for new OLPL materials. The investigation of the material provides valuable insights toward the generation of OLPL from a single-component system.
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