The fluorescence–phosphorescence dual solvoluminescence (SL) of water-soluble metal nanoclusters (NCs) at room temperature was successfully achieved by a simple solvent-stimulated strategy. The strong interaction between carboxylate ligands and the metal core at the nanoscale interface not only induces rigid conformations of carbonyl groups but also affords a perfect carbonyl cluster that acts as an exact chromophore of metal NCs for aggregation-induced emission (AIE) mechanics. The clustering of carbonyl groups bearing on the polymer backbone chain is promoted by newly discovered n → π* noncovalent interactions. The efficient delocalization of electrons in overlapped C═O double bonds between neighboring carbonyl groups triggered by strong n → π* interactions in the polymer cluster accounts for its unique SL properties, especially the abnormal phosphorescence. This was further confirmed by controlled experiments for the presence of intersystem crossing (ISC) transitions. The results provide novel insights for understanding the complex SL process and open up a new way to study the inherent mechanism of SL by broadening the application of metal NCs.

We report silver nanoparticles (Ag NPs) with high stability, sensitivity, and no surface enhanced Raman scattering (SERS) background. The Ag NPs were synthesized via a one-step process with polysodium styrenesulfonate (PSSS) templates, and they could efficiently adsorb polycyclic aromatic molecules via π–π stacking. The adsorption mechanisms and applicability were systematically studied by experimental measurements and theoretical simulations. When the polycyclic aromatic analytes were adsorbed on the PSSS-templated Ag NPs, the vibrations of π–π stacking-bound moieties were attenuated, yet those of the other unbound aromatic moieties increased. Most importantly, when the analytes had more than two π–π stacking binding sites, the PSSS-templated Ag NPs could trap the analytes by focusing through the optical force induced or via the simultaneously formed analyte–Ag NPs aggregates. This afforded high SERS intensity and very low detection limits.

pH plays a vital role in various cellular activities, and real-time observation of the intracellular pH through a pH indicator is very important for studying many physiological processes. In this paper, we studied the pH response of Trp–Trp dipeptide and its derivatives (NATrp2Me, NBTrp2 and Trp2Me) by steady-state and time-resolved fluorescence spectroscopy. Both the fluorescence intensities and lifetimes of Trp–Trp dipeptide as well as Trp2Me were functions of pH in the physiological range from 5.5 to 9.0. However, NATrp2Me and NBTrp2 showed no difference. The exposed amino was found to be pivotal for its pH dependence. Moreover, an artificially synthesized tetrapeptide (Trp–Trp–Ala–Ser) confirmed the pH sensitivity of N-terminal Trp–Trp residues. The pH values could be quantitatively determined from the fluorescence intensities and lifetimes of the N-terminal Trp–Trp residue. Thus, the N-terminal Trp–Trp residues may be fused into the polypeptides/proteins to serve as an intrinsic pH indicator in fluorescence spectroscopy and imaging.

•We studied the Trp–Trp dipeptide via ps and fs resolved fluorescence spectroscopy.•The quantum yields and lifetime of Trp–Trp dipeptide are smaller than single Trp.•Candidate mechanisms are discussed.•Electrons transfer and the two Trp residues interaction are proposed.Ultrafast fluorescence dynamics of Tryptophan–Tryptophan (Trp–Trp/Trp2) dipeptide and its derivatives in water have been investigated using a picosecond resolved time correlated single photon counting (TCSPC) apparatus together with a femtosecond resolved upconversion spectrophotofluorometer. The fluorescence decay profiles at multiple wavelengths were fitted by a global analysis technique. Nanosecond fluorescence kinetics of Trp2, N-tert-butyl carbonyl oxygen-N′-aldehyde group-l-tryptophan-l-tryptophan (NBTrp2), l-tryptophan-l-tryptophan methyl ester (Trp2Me), and N-acetyl-l-tryptophan-l-tryptophan methyl ester (NATrp2Me) exhibit multi-exponential decays with the average lifetimes of 1.99, 3.04, 0.72 and 1.22 ns, respectively. Due to the intramolecular interaction between two Trp residues, the “water relaxation” lifetime was observed around 4 ps, and it is noticed that Trp2 and its derivatives also exhibit a new decay with a lifetime of ∼100 ps, while single-Trp fluorescence decay in dipeptides/proteins shows 20–30 ps. The intramolecular interaction lifetime constants of Trp2, NBTrp2, Trp2Me and NATrp2Me were then calculated to be 3.64, 0.93, 11.52 and 2.40 ns, respectively. Candidate mechanisms (including heterogeneity, solvent relaxation, quasi static self-quenching or ET/PT quenching) have been discussed.

Using carboxylate-protected silver nanoclusters (Ag-carboxylate NCs) as a model, we separately investigated the contribution of the ligand shell and the metal core to understand the nature of photoluminescence of Ag NCs. A new Ag(0)NCs@Ag(I)-carboxylate complex core–shell structural model has been proposed. The emission from the Ag-carboxylate NCs could be attributed to ligand-to-metal–metal charge transfer from Ag(I)-carboxylate complexes (the oxygen atom in the carboxylate ligands to the Ag(I) ions) to the Ag atoms and subsequent radiative relaxation. Additionally, we found that the emission wavelength of the Ag NCs depends on the excitation wavelength implying a strong coupling between surface plasmon and emitter in Ag NCs. The strong coupling between the surface plasmon and the emitter determines the quantum yield and lifetime. The emission mechanism of Ag NCs and its relation to the organic templates and metal cores were clearly clarified. The results should stimulate additional experimental and theoretical research on the molecular-level design of luminescent metal probes for optoelectronics and other applications.