Synthesis, Light Emission, Nanoaggregation, and Restricted Intramolecular Rotation of 1,1-Substituted 2,3,4,5-Tetraphenylsiloles

Abstract

A series of ten 2,3,4,5-tetraphenylsiloles with different 1,1-substituents [XYSi(CPh)4] were prepared, and three of these, i.e., 1,1,2,3,4,5-hexaphenylsilole [X = Y = Ph (3)], 1-ethynyl-1,2,3,4,5-pentaphenylsilole [X = Ph, Y = C⋮CH (15)], and 1,1-bis(phenylethynyl)-2,3,4,5-tetraphenylsilole [X = Y = C⋮CPh (18)], were characterized crystallographically. The ground- and excited-states of the siloles were influenced by the inductive effect of the 1,1-substituents: with an increase in their electronegativity, the absorption and emission spectra of the siloles bathochromically shifted. A simple and reliable TLC-based method was developed for measurement of the solid-state luminescence spectra of the siloles. When molecularly dissolved in common solvents at room temperature, all the siloles were practically nonemissive (“off”). When poor solvents were added, the silole molecules clustered into nanoaggregates, which turned the emission “on” and boosted the photoluminescence quantum yields by up to 2 orders of magnitude (aggregation-induced emission). The silole emission could also be greatly enhanced by increasing the viscosity and decreasing the temperature of the silole solutions. The solution thickening and cooling experiments suggest that the aggregation-induced emission is caused by the restricted intramolecular rotations of the peripheral aromatic rings upon the axes of the single bonds linked to the central silole cores.

Structural Modulation of Solid‐State Emission of 2,5‐Bis(trialkylsilylethynyl)‐3,4‐diphenylsiloles

“…Their fluorescence quantum yields (F F ) are low (0.32-1.67 %), but are somewhat higher than that of HPS (0.1 %), [6] owing to their more conjugated electronic structures.…”

“…[5,6] The key intermediate 2,5-dibromosiloles (3) were prepared by bromination of 2 with NBS. Cross-coupling of 3 with alkynes gave the target products (4-6) in high yields (83-95 %).…”

Light-Up of Rhodamine Hydrazide to Generate Emissive Initiator for Polymerization and to Afford Photochromic Polypeptide Metal Complex

“…R-PLG 23 contains higher α-helical chain and its R-O moiety should be more hampered in rotation compared to R-O in R-PLG 13 . Since RIR [23,31,32] is the mechanism responsible for AIE, R-PLG 23 with high content of α-helical chains should be more efficient in emission compared to R-PLG 13 . …”

“…Because of short lifetime and low quantum efficiency of the photoinduced reaction, few investigations [26][27][28][29] were aimed at the photochromic properties of rhodamine amides over the next 30 years. However, recent progress suggested that metal complex (RhM-C, Scheme 1) of rhodamine B salicylaldehyde hydrazine [30] Effective restriction [23,31,32] on the intramolecular rotation of AIE-active luminogens is the main mechanism behind AIE phenomenon. Many luminogens [17][18][19][20][21][22][23] with inherent rotational restriction have been characterized to exhibit AIE activity.…”

Aggregation-induced delayed fluorescence from phenothiazine-containing donor–acceptor molecules for high-efficiency non-doped organic light-emitting diodes

“…This AIE phenomenon can be explained by the restriction of non-radiative vibrational relaxation processes in the aggregated solid state. Representative examples of AIE-active fluorophores include siloles, [6][7][8][9] cyanostilbenes, [10][11][12] o-carborane derivatives [13][14][15][16][17] and tetraphenylethenes [18][19][20][21][22][23] . Some of these fluorophores have proved useful as non-doped emission layers in fluorescent OLEDs.…”