in the past years due to their advantages of low cost, less toxicity, readily accessible structure change, [2] and easy color tuning. [3] Such organic materials show wide applications in bio-imaging/sensing, [4] encryption/anti-counterfeiting, [5] and organic light-emitting diode (OLED), [6] etc. As well known, carbazole (Cz) derivatives are considered as the promising light emitters or hole-transporting materials. In particular, the coplanar configuration of carbazole is in favor of electron communication or charge carrier mobility. [7] Hundreds of papers have been published [8] since the H-aggregation of carbazole derivatives was reported to stabilize the triplet excited states for ultralong organic phosphorescence (UOP) in 2015, [1b] and these molecules provide a new way to fabricate the UOP materials.Interestingly, Liu et al. recently reported their findings that the commercially available carbazole was inevitably mixed with trace carbazole isomer (1H-benzo[ f ] indole, Bd), and Bd was believed to be involved in the origination of UOP. [1c,9] They suggested that Cz and Bd moieties in close proximity acted as a microplanar heterojunction to generate photo-induced charge-separated states, and further to produce intense UOP. Based on their results, the UOP of carbazole derivatives previously presented in the literature are actually integrated luminescent properties of carbazole derivatives and Bd's counterparts. [1b,4c,10] Up to now, the intrinsic photophysical property of the pure Bd's counterpart remains unclear because the purified Bd by refining the commercial Cz via high resolution liquid chromatography (HPLC) unavoidably contains trace carbazole, which limits the clear elucidation of the mechanism of Cz-and Bd-based UOP. Therefore, to understand the truth of Cz-and Bd-based UOP is still an unsolved problem and remains full of challenges.Herein, we report the synthesis of four Cz/Bd derivatives (Figure 1a,b) with different substitution numbers of Bd in the structure and aim to deeply understand the role of Bd in UOP. To physically isolate Cz and Bd, we synthesized Cz and Bd separately in our lab. According to the experimental results, such as temperature-variable photoluminescence (PL) spectra, electron spin resonance (ESR) spectra, dual-component doping The mechanism of carbazole (Cz)-based phosphors is still unclear since its isomer (1H-benzo[f ]indole, Bd) is discovered in 2020. Herein, the successful synthesis of four Cz/Bd derivatives is reported, named as 2CzBr, CzBdBr, 2BdBr, and 3Bd, and the general mechanism for their ultralong organic phosphorescence (UOP) is provided. Bd and its derivatives give double groups of phosphorescence, including the short-wavelength phosphorescence with a short lifetime and the ultralong phosphorescence at long wavelengths, assigned to their neutral molecules and radical cations, respectively. Interestingly, the doped poly(methyl methacrylate) (PMMA) films of CzBdBr and 2BdBr show photo-activated ultralong phosphorescence at room temperature. The activation of ...

A novel class of organic units (N‐1 and N‐2) and their derivatives (PNNA‐1 and PNNA‐2) with excellent property of ultralong organic room temperature phosphorescence (UORTP) is reported. In this work, N‐1, N‐2, and their derivatives function as the guests, while organic powders (PNCz, BBP, DBT) and polymethyl methacrylate (PMMA) serve as the host matrixes. Amazingly, the color of phosphorescence can be tuned in different states or by varying the host matrixes. At 77 K, all molecules show green afterglow in the monomer state but yellow afterglow in the aggregated state because strong intermolecular interactions exist in the self‐aggregate and induce a redshift of the afterglow. In particular, PNNA‐1 and PNNA‐2 demonstrate distinctive photoactivated green UORTP in the PMMA film owing to the generation of their cation radicals. Whereas the PNNA‐1@PNCz and PNNA‐2@PNCz doping powders give out yellow UORTP, showing matrix‐controlled color‐tunable UORTP. In PNCz, the cation radicals of PNNA‐1 and PNNA‐2 can stay stably and form strong intermolecular interactions with PNCz, leading to a redshift of ultralong phosphorescence.

Phosphorescence selective expression in the development of ultralong organic room-temperature phosphorescence (UORTP) materials to enrich the properties and functions of smart materials is a very interesting topic but has not been realized yet due to the lack of organic phosphorescence units. In this work, we, for the first time, investigate the selective expression phenomenon of two organic phosphorescence units in a single molecule. First, we report a new phosphorescence unit 7H-benzo[c]carbazole (BCz) with the advantage of simple synthesis. BCz derivatives (PNBCz-1 and PNBCz-2) feature photoactivated green ultralong phosphorescence in the PMMA film at room temperature, and cation radicals are involved in the unique ultralong phosphorescence behavior, which is similar to H-benzo[f]indole (Bd) derivatives. Different from Bd, pure powders of BCz derivatives show intense red-shifted ultralong phosphorescence at 77 K, probably due to the extended π conjugated structure of BCz. Then, BCz and Bd were incorporated into a single skeleton and two asymmetric molecules (PNBCzBd-1 and PNBCzBd-2) were obtained. Surprisingly, in the PMMA film, PNBCzBd-1 and PNBCzBd-2 both show photoactivated yellow ultralong phosphorescence at room temperature assigned to the intrinsic phosphorescence emission of Bd, and intrinsic green phosphorescence of BCz is almost screened by Bd. Density functional theory (DFT) calculations reveal that the incorporation of Bd leads to the shifting of the phosphorescence emission centers from BCz units to Bd units. Therefore, the intrinsic phosphorescence emission of Bd is selectively expressed in the case of PNBCzBd-1 and PNBCzBd-2. To our best knowledge, this is the first example that reports the selective expression behavior of organic phosphorescence units. We believe that this study may impact the future research of UORTP materials and lay the foundation for their future applications.

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How matrixes influence room temperature ultralong organic phosphorescence (RTUOP) in the doping systems is a fundamental question. In this study, we construct guest-matrix doping phosphorescence systems by using the derivatives (ISO2N-2, ISO2BCz-1, and ISO2BCz-2) of three phosphorescence units (N-2, BCz-1, and BCz-2) and two matrixes (ISO2Cz and DMAP) and systematically investigate their RTUOP properties. Firstly, the intrinsic phosphorescence properties of three guest molecules were studied in solution, in the pure powder state, and in PMMA film. Then, the guest molecules were doped into the two matrixes with increasing weight ratio. To our surprise, all of the doping systems in DMAP feature a longer lifetime but weaker phosphorescence intensity, while all of the doping systems in ISO2Cz exhibit a shorter lifetime but higher phosphorescence intensity. According to the single-crystal analysis of the two matrixes, resemblant chemical structures of the guests and ISO2Cz enable them to approach each other and interact with each other via a variety of interactions, thus facilitating the occurrence of charge separation (CS) and charge recombination (CR). The HOMO-LUMO energy levels of the guests match well with the ones of ISO2Cz, which also significantly promotes the efficiency of the CS and CR process. To our best knowledge, this work is a systematic study on how matrixes influence the RTUOP of guest-matrix doping systems and may give deep insight into the development of organic phosphorescence.