Modulation of Aggregation‐Induced Emission and Electroluminescence of Silole Derivatives by a Covalent Bonding Pattern

Abstract

The deciphering of structure-property relationships is of high importance to rational design of functional molecules and to explore their potential applications. In this work, a series of silole derivatives substituted with benzo[b]thiophene (BT) at the 2,5-positions of the silole ring are synthesized and characterized. The experimental investigation reveals that the covalent bonding through the 2-position of BT (2-BT) with silole ring allows a better conjugation of the backbone than that achieved though the 5-position of BT (5-BT), and results in totally different emission behaviors. The silole derivatives with 5-BT groups are weakly fluorescent in solutions, but are induced to emit intensely in aggregates, presenting excellent aggregation-induced emission (AIE) characteristics. Those with 2-BT groups can fluoresce more strongly in solutions, but no obvious emission enhancements are found in aggregates, suggesting they are not AIE-active. Theoretical calculations disclose that the good conjugation lowers the rotational motions of BT groups, which enables the molecules to emit more efficiently in solutions. But the well-conjugated planar backbone is prone to form strong intermoelcular interactions in aggregates, which decreases the emission efficiency. Non-doped organic light-emitting diodes (OLEDs) are fabricated by using these siloles as emitters. AIE-active silole derivatives show much better elecroluminescence properties than those without the AIE characterisic, demonstrating the advantage of AIE-active emitters in OLED applications.

Aggregation-induced emission of siloles

“…The connection of the 2-position of the BT groups to the 2,5-positions of the silole furnishes a well-conjugated backbone within the molecules, leading to greatly red-shifted absorption maxima for 2-BTDMS (432 nm) and 2-BTMPS (437 nm) relative to 5-BTDMS (370 nm) and 5-BTMPS (375 nm). 38 Like most 2,3,4,5-tetraphenylsilole derivatives, 5-BTDMS and 5-BTMPS show weak fluorescence peaks at 488 and 499 nm, with low Φ F values of 0.8% and 1.2% in THF solution. Their solid films, however, are highly emissive with close emission peaks at 494 and 502 nm and high Φ F values of 60.4% and 53.0%, revealing that they are AIE-active.…”

How a Small Structural Difference Can Turn Optical Properties of π‐Extended Coumarins Upside Down: The Role of Non‐Innocent Saturated Rings

“…Both fluorescence and phosphorescence enhancement based on aggregation effects has been explored for organic materials. The importance of the exploitation of this phenomenon has been emerged when applied to organic light‐emitting diodes (OLEDs) . Although the majority of studied compounds contain tetraphenylethylene as the key structural element, or analogous ethenes bearing CN groups, other, less typical architectures are also described from time to time .…”

“…The importance of the exploitation of this phenomenon has been emerged when applied to organic light-emitting diodes (OLEDs). [8] Although the majority of studied compounds contain tetraphenylethylene as the key structurale lement, [9] or analogous ethenesb earing CN groups, [10] other,l ess typical architectures are also described from time to time. [11] Conceivably,m olecules displaying excited-state intramolecular protont ransfer (ESIPT) [12,13] constitute the second largest group of compounds displaying AIEE.…”

Solid‐State Photochromism by Molecular Assembly of Bis‐o‐carboranyl Siloles

“…The most notable features come from the dihedral angle between the silole ring and the 2,5‐positional benzene rings; depending on both the substituents and their positions, the dihedral angles between the silole ring and benzene rings at the C2 and C5 positions varied between 128.4° and 110.3° for C Si‐ m ‐Cb and C Si‐ p ‐Cb , respectively, as shown in Figure . Therefore, the different dihedral angles between the silole ring and benzene rings at the C2 and C5 positions of C Si‐ m ‐Cb and C Si‐ p ‐Cb would result in different emission properties . As the silole ring and benzene rings in C Si‐ p ‐Cb are positioned orthogonally, there would be negligible electronic coupling between the silole and end‐on o ‐carboranes.…”

“…Therefore, the different dihedral angles betweent he silole ring and benzene rings at the C2 and C5 positions of C Si-m-Cb and C Si-p-Cb would result in different emission properties. [50] As the silole ring and benzene rings in C Si-p-Cb are positioned orthogonally,t here would be negligible electronic coupling between the silole and end-on o-carboranes. By contrast, the crystal structureo fC Si-m-Cb showeda more horizontally tilted geometry between the silole ring and benzene rings at the C2 and C5 positions because of the sterically demanding conformation.…”