Abstract
Further development of high-efficiency and low-cost organic fluorescent materials is intrinsically hampered by the energy gap law and spin statistics, especially in the near-infrared (NIR) region. Here we design a novel building block with aggregation-induced emission (AIE) activity for realizing highly efficient luminophores covering the deep-red and NIR region, which originates from an increase in the orbital overlap and electron-withdrawing ability. An organic donor–acceptor molecule (BPMT) with the building block is prepared and can readily form J-type molecular columns with multiple C–H⋯N/O interactions. Notably, such synthesized materials can emit fluorescence centered at 701 nm with extremely high photoluminescence quantum yields (PLQYs) of 48.7%. Experimental and theoretical investigations reveal that the formation of the hybridized local and charge-transfer (HLCT) state and substantial C–H⋯N/O interactions contribute to a fast radiative decay rate and a slow nonradiative decay rate, respectively, resulting in high PLQYs in the solid state covering the NIR range. Remarkably, such BPMT crystals, as a first example, reveal strong-penetrability piezochromism along with a distinct PL change from the deep-red (λmax = 704 nm) to NIR (λmax = 821 nm) region. Moreover, such typical AIE-active luminophores are demonstrated to be a good candidate as a lasing medium. Together with epoxy resin by a self-assembly method, a microlaser is successfully illustrated with a lasing wavelength of 735.2 nm at a threshold of 22.3 kW cm−2. These results provide a promising approach to extend the contents of deep-red/NIR luminophores and open a new avenue to enable applications ranging from chemical sensing to lasing.
Highlights
Near-infrared (NIR) light-emitting materials have attracted growing attention in recent years, with diverse applications including biotherapy, night-vision, up-conversion lasers and so on.1 Compared with inorganic NIR materials, organic NIR materials are inexpensive and feasible for fabrication, and their diverse structures enable fruitful possibilities for the abovementioned applications
The synthetic route of the NIR chromophore BPMT is illustrated in Scheme 1, and more detailed procedures are shown in the Experimental section
Multiple inter-molecular noncovalent interactions (C–H/O, C–H/N, etc.) can be constructed in the aggregated state through the introduction of methoxyl and cyanoyl groups,13 which contribute to the restriction of intramolecular motions (RIMs) and enhancement of photoluminescence quantum yields (PLQYs)
Summary
Have already been proven to be an effective solution to overcome the low efficiency problem, the cost and preparation problem remain since the fabrication process includes noble metal complex material systems. This method sterically limits the p–p molecular stacking responsible for aggregation quenching and restricts the intramolecular motions of peripheral rings Another method is to directly regulate the excited state component for an enhanced radiative transition rate of a D–A luminophore, known as the hybridized local and charge-transfer (HLCT) method.. As the cyano group has an electronwithdrawing character, triphenylamine (TPA)-modi ed CSB derivatives usually exhibited a typical CT behaviour Their uorescence rarely covered the deep-red/NIR region.. Wavefunction overlap between “hole” and “particle” is clearly observed on the CSB unit, facilitating the construction of the HLCT state.7b In this study, for developing deep-red/NIR PL materials, we constructed a new-style building block, TPAN, as shown in Scheme 1, by the introduction of a benzo[c] [1,2,5]thiadiazole (BTA) unit This strategy is based on the following considerations. To the best of our knowledge, this is a rst example of a uorophore showing piezochromic behaviour covering the deep-red and NIR region (>700 nm).1f,10 Inspired by its excellent AIE behaviour, a BPMT-based laser was successfully achieved
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