Aggregation-Induced Fluorescence-to-Phosphorescence Switching of Molecular Gold Clusters

Abstract

Aggregation-induced optical responses are ubiquitous among a wide range of organic and inorganic compounds. Here, we demonstrate an unprecedented effect of aggregation on the photoluminescence (PL) profiles of [core + exo]-type [Au] clusters, which displayed a change in the dominant PL emission mode from fluorescence to phosphorescence-type upon aggregation. In solvents in which cluster molecules are highly soluble and exist as monomers, they displayed single PL bands at ∼600 nm at ambient temperatures. However, in solvents in which cluster molecules are less soluble and cluster aggregation is induced, a new PL band at ∼700 nm also emerged. Lifetime measurements revealed that the PL emissions at ∼600 and ∼700 nm had fluorescence and phosphorescence characters, respectively. Studies of the excitation spectra suggested that organized cluster assemblies were responsible for the lower-energy emission at ∼700 nm and had exceptionally high emission activity. Accordingly, intense phosphorescence-type emissions were observed in the solid state in which the quantum efficiencies were higher by two orders of magnitude than those of the corresponding monomeric forms in solution. This work provides an example of the critical effects of cluster aggregation events on their optical properties and shows the potential of such effects in the design of cluster-based materials with unique functions and properties.

Self‐Assembly of a Monochromophore‐Based Polymer Enables Unprecedented Ratiometric Tracing of Hypoxia

“…Upon photoexcitation at 595 nm, not only did the assembled Pt‐TPP‐PVP 430 give an oxygen‐sensitive phosphorescent emission up to ≈ 760 nm, but also exhibited another fluorescent emission band at 660 nm (Figures S1 and S2, Supporting Information). Here, the fluorescent emission at 660 nm was very dependent upon the specific assembly with efficient length of PVP chains, which might be resulted from the assembled clusters of the hydrophilic backbone PVP chain . The efficient length of PVP chains has two critical effects in Pt‐TPP‐PVP n ( n ≥ 200): i) generation of cluster‐induced fluorescent emission at 660 nm; ii) making the Pt‐porphyrin phosphorescent emission shift from 655 to 760 nm (Figures S3–S5, Supporting Information).…”

Unusual Attractive Au–π Interactions in Small Diacetylene‐Modified Gold Clusters

“…in 2012, but crystal structure determination was not achieved. We have also introduced alkynyl ligands as coligands into Au 8 and Au 13 clusters and showed the substantial perturbation effects of particular π‐electron systems on the electronic properties of the gold clusters . Furthermore, Wang et al have recently reported numerous homoleptic and heteroleptic alkynyl‐protected gold clusters, demonstrating the formation of various surface Au I ‐acetylide motifs such as C≡C−Au−C≡C and C≡C−Au−C≡C−Au−C≡C .…”

Unusual Attractive Au–π Interactions in Small Diacetylene‐Modified Gold Clusters

“…Suchweak interactions are not found in monoacetylene-modified clusters,w hichi ndicates that they are specific for diacetylenic ligands.T he attractive Au-p interactions are likely associated with the low energy of the p*orbital in the diacetylenic moieties,into which the valence electrons of the gold core may be backdonated. [12][13][14][15] Furthermore,W ang et al have recently reported numerous homoleptic and heteroleptic alkynylprotected gold clusters,d emonstrating the formation of various surface Au I -acetylide motifs such as C C À Au À C C and C C À Au À C C À Au À C C. [16][17][18][19][20] These motifs are analogous to the staple units found in thiolate-protected clusters, but their capability to accommodate additional gold atoms through p-coordination should be noted. [1][2][3][4][5][6] Thiolates [1][2][3] and phosphines [6][7][8][9][10] have been frequently used as protecting ligands,w hile alkynyl (acetylide) ligands have recently emerged as unique and suitable ligands that stabilize gold clusters.…”

“…[1][2][3][4][5][6] Thiolates [1][2][3] and phosphines [6][7][8][9][10] have been frequently used as protecting ligands,w hile alkynyl (acetylide) ligands have recently emerged as unique and suitable ligands that stabilize gold clusters. [12][13][14][15] Furthermore,W ang et al have recently reported numerous homoleptic and heteroleptic alkynylprotected gold clusters,d emonstrating the formation of various surface Au I -acetylide motifs such as C C À Au À C C and C C À Au À C C À Au À C C. [16][17][18][19][20] These motifs are analogous to the staple units found in thiolate-protected clusters, but their capability to accommodate additional gold atoms through p-coordination should be noted. We have also introduced alkynyl ligands as coligands into Au 8 and Au 13 clusters and showed the substantial perturbation effects of particular p-electron systems on the electronic properties of the gold clusters.…”