Highly Efficient Luminescence from Charge-Transfer Gold Nanoclusters Enabled by Lewis Acid

Abstract

Understanding the complicated intramolecular charge transfer (ICT) behaviors of nanomaterials is crucial to the development of high-quality nanoluminophores for various applications. However, the ICT process in molecule-like metal nanoclusters has been rarely explored. Herein, a proton binding-induced enhanced ICT state is discovered in 6-aza-2-thiothymine-protected gold nanoclusters (ATT-AuNCs). Such an excited-state electron transfer process gives rise to the weakened and red-shifted photoluminescence of these nanoclusters. By the joint use of this newfound ICT mechanism and a restriction of intramolecular motion (RIM) strategy, a red shift in the emission maxima of 30 nm with 27.5-fold higher fluorescence quantum efficiency is achieved after introducing rare-earth scandium ion (Sc3+) into ATT-AuNCs. Furthermore, it is found that upon the addition of Sc3+, the photoinduced electron transfer (PET) rate from ATT-AuNCs to minocycline is largely accelerated by forming a donor–bridge–acceptor structure. This paper offers a simple method to modulate the luminescent properties of metal nanoclusters for the rational design of next-generation sensing platforms.

Viewing Aggregation-Induced Emission of Metal Nanoclusters from Design Strategies to Applications

“…Recently, researchers have focused their attention on the rare earth ions. Luminogen ATT-AuNCs (ATT: 6-aza-2-thiothymine) are discussed here as a representation [ 33 ]. It was discovered that the luminescence properties of ATT-Au NCs significantly depend on the pH.…”

Poly(vinyl alcohol)-Coated Au Nanoclusters with High Stability and Quantum Yields of Fluorescence for Application in pH Sensing

“…As mentioned previously, a strong electrostatic dipole−dipole interaction (hydrogen bonds) was formed between AuNCs and PVA, which accelerated the effective electron transfer and resulted in fluorescence emission enhancement. 53,54 Meanwhile, hydrogen bonding interactions were broken due to the addition of DMSO, which blocked the aggregation of AuNCs, and the blueshift disappeared. In order to discuss this further, the luminescence spectra of AuNCs@AMP/PVA in the D 2 O were monitored.…”

Triple Ligand Engineered Gold Nanoclusters with Enhanced Fluorescence and Device Compatibility for Efficient Electroluminescence Light-Emitting Diodes

“…Further global fitting of ESA kinetic traces of Au NCs presents four decay components of 0.58 ps, 5.03 ps, 72.5 ps, and >2 ns for ATT-Au NCs, 0.53 ps, 5.25 ps, 80.7 ps, and >2 ns for Arg/ATT-Au NCs, and 0.51 ps, 5.78 ps, 92.3 ps, and >2 ns for TOAB/Arg/ATT-Au NCs (Table S2). As shown in Figure S9, the decay components with long lifetimes (>2 ns) are attributed to the radiative transition from S 1 excited state to S 0 ground state. ,, The fractional picosecond decay components can be assigned to the internal conversion of hot electrons excited by high-energy pump beam from S n state to S 1 state . Since there is no activated triplet state, the decay components with few picoseconds and dozens of picoseconds are attributed to the solvent relaxation induced by solute–solvent interaction, and delayed vibrational relaxation (VR) in S 1 state, respectively. , It should be mentioned that the delayed VR is the main nonradiative pathway of the Au NCs, which redistributes the density of excited electrons by cooling them to the lowest S 1 state. , The TOAB/Arg/ATT-Au NCs exhibit the slowest delayed VR process, indicating that the triple ligand engineering strategy effectively inhibits the vibrational relaxation of the excited state, thus enhancing the PLQYs of Au NCs and strengthening the competitiveness in EL-LED applications.…”

“…After Arg modification, a new lowest-energy absorption peak appears at 498 nm and remains after TOAB modification, which indicates that Arg modification leads to the redistribution of the excited state. 28,30,40 Both Arg/ATT-Au NCs and TOAB/Arg/ATT-Au NCs exhibit emission peaks at 532 nm with a fwhm around 30 nm (Figure 1c). In comparison to ATT-Au NCs, the PLQY of Arg/ATT-Au NCs exhibits a 20-times enhancement to 39.2%; meanwhile, the PLQY of TOAB/Arg/ATT-Au NCs is further improved to 73.4% (Table S1).…”

“…These results demonstrate that the modification of Arg initiates the re-excitation channels from high excited states to relatively low ones. 40,41 This process effectively increases the absorption cross-section and the radiative decay rates of Arg/ ATT-Au and TOAB/Arg/ATT-Au NCs. 30 The normalized ESA and GSB kinetic traces show that the ATT-Au NCs exhibit the fastest decays and TOAB/Arg/ATT-Au NCs exhibits the slowest decays (Figure 2d S2).…”