Interface Engineering of Bi‐Fluorescence Molecules for High‐Performance Data Encryption and Ultralow UV‐Light Detection

Abstract

It is extremely difficult if not impossible to effectively and precisely regulate the luminescence of organic chromophores from different electronic excited states through external stimuli for use in light‐conversion devices. This is mainly due to the difficulty in breaking Kasha's rule by large energy separation and stabilization of different emissive electronic excited states. Here, the authors address this great challenge in a single experiment by expanding the utility of a monounsaturated omega‐9 fatty acid (oleic acid) capped with organic chromophores as a new and efficient luminescent regulator. More specifically, the authors have successfully promoted the use of oleic acid as an efficient and reversible switch that can precisely regulate chromophore luminescence. These time‐resolved absorption and luminescence experiments, along with density functional theory calculations have clearly demonstrated that ultrafast electron transfer from oleic acid to the difluoroboron β‐diketonate (DFBK) chromophores efficiently blocks the intramolecular charge transfer process of DFBK chromophores, and activates the locally excited state luminescence, leading to different emission colors from different electronic excited states for ultralow UV‐light detection and high‐performance data encryption.

Tunable Photoinduced Charge Transfer at the Interface between Benzoselenadiazole-Based MOF Linkers and Thermally Activated Delayed Fluorescence Chromophore

“…These features, such as the presence of new emission bands and considerable PL quenching, could be related to intermolecular electron transfer from the donor molecule (Ac-SDZ) to the acceptor molecule (TADF), and locally excited-state formation. 6 , 18 , 29 This observation provides another piece of evidence of the charge transfer process in this system. In other words, based on the absorption and emission spectroscopic measurements, we can assign the peak at 500 nm to the locally excited-state formation in Ac-SDZ caused by the intermolecular charge transfer phenomenon between Ac-SDZ and the TADF molecule.…”

“…The emission band of the TADF molecule at 620 nm was also observed with a much lower intensity than in the SDZ–TADF system. These features, such as the presence of new emission bands and considerable PL quenching, could be related to intermolecular electron transfer from the donor molecule (Ac-SDZ) to the acceptor molecule (TADF), and locally excited-state formation. ,, This observation provides another piece of evidence of the charge transfer process in this system. In other words, based on the absorption and emission spectroscopic measurements, we can assign the peak at 500 nm to the locally excited-state formation in Ac-SDZ caused by the intermolecular charge transfer phenomenon between Ac-SDZ and the TADF molecule. , The formation of this locally excited-state band in Ac-SDZ (500 nm) is a consequence of the new charge density distribution after the charge transfer to the TADF molecule.…”

“…In other words, based on the absorption and emission spectroscopic measurements, we can assign the peak at 500 nm to the locally excited-state formation in Ac-SDZ caused by the intermolecular charge transfer phenomenon between Ac-SDZ and the TADF molecule. , The formation of this locally excited-state band in Ac-SDZ (500 nm) is a consequence of the new charge density distribution after the charge transfer to the TADF molecule. Additionally, the second band around 550 nm is attributed to the original charge transfer state of Ac-SDZ molecule. − From these steady-state measurements, we can summarize that the presence of a CC bond in the Ac-SDZ molecule can change its optical properties relative to the SDZ molecule in the presence of the acceptor, suggesting the important role of this bridge in controlling photochemical processes at the interface of the donor–acceptor system.…”

“…One interesting family of chromophores that involves the control of different excited states is thermally activated delayed fluorescence (TADF) molecules, which have attracted substantial attention as luminescent materials due to their unique ability to harvest often detrimental triplet states as emissive singlet states through the reverse intersystem crossing process. − This phenomenon prolongs the fluorescence lifetime of TADF materials from nanoseconds to microseconds, , making them excellent candidates for several applications as luminescence sensors, − organic light-emitting devices (OLEDs), ,,, and more recently, as X-ray imaging materials. − However, due to the intricate interplay between the triplet and singlet excited states in TADF, it is challenging to control the optical properties of TADF materials by direct structural modifications, but they can serve as excellent energy and/or electron acceptor units. ,,,,,,− Other promising luminescent materials are heterobenzodiazole rings, which have also demonstrated excellent luminescent and photochemical behaviors. − Unlike TADF materials, the structures of these organic linkers can be easily altered to achieve different reaction outcomes upon light excitation, and they can serve as energy/electron donors in a variety of chemical composites. ,, Moreover, this kind of organic linker is designed to be an easy building block of metal–organic frameworks (MOFs) − that can serve not only to improve the optical properties of MOFs but also to favor and increase the efficiency of energy transfer processes at the donor–acceptor interface due to the highly ordered structure of the frameworks. These properties have been exploited in sensing, ,− catalysis, − and light-harvesting applications, i...…”

“… 20 − 24 However, due to the intricate interplay between the triplet and singlet excited states in TADF, it is challenging to control the optical properties of TADF materials by direct structural modifications, but they can serve as excellent energy and/or electron acceptor units. 2 , 5 , 8 , 11 , 18 , 19 , 25 − 27 Other promising luminescent materials are heterobenzodiazole rings, which have also demonstrated excellent luminescent and photochemical behaviors. 28 − 34 Unlike TADF materials, the structures of these organic linkers can be easily altered to achieve different reaction outcomes upon light excitation, and they can serve as energy/electron donors in a variety of chemical composites.…”