π-Conjugated Cyanostilbene Derivatives: A Unique Self-Assembly Motif for Molecular Nanostructures with Enhanced Emission and Transport

Abstract

π-Conjugated organic molecules represent an attractive platform for the design and fabrication of a wide range of nano- and microstructures for use in organic optoelectronics. The desirable optical and electrical properties of π-conjugated molecules for these applications depend on their primary molecular structure and their intermolecular interactions such as molecular packing or ordering in the condensed states. Because of the difficulty in satisfying these rigorous structural requirements for photoluminescence and charge transport, the development of novel high-performance π-conjugated systems for nano-optoelectronics has remained a challenge. This Account describes our recent discovery of a novel class of self-assembling π-conjugated organic molecules with a built-in molecular elastic twist. These molecules consist of a cyano-substituted stilbenic π-conjugated backbone and various terminal functional groups, and they offer excellent optical, electrical, and self-assembly properties for use in various nano-optoelectronic devices. The characteristic "twist elasticity" behavior of these molecules occurs in response to molecular interactions. These large torsional or conformational changes in the cyanostilbene backbone play an important role in achieving favorable intermolecular interactions that lead to both high photoluminescence and good charge carrier mobility in self-assembled nanostructures. Conventional π-conjugated molecules in the solid state typically show concentration (aggregation) fluorescence quenching. Initially, we describe the unique photoluminescence properties, aggregation-induced enhanced emission (AIEE), of these new cyanostilbene derivatives that elegantly circumvent these problems. These elastic twist π-conjugated backbones serve as versatile scaffolds for the preparation of well-defined patterned nanosized architectures through facile self-assembly processes. We discuss in particular detail the preparation of 1D nanowire structures through programmed self-assembly. This Account describes the importance of utilizing AIEE effects to explore optical device applications, such as organic semiconducting lasers (OSLs), optical memory, and sensors. We demonstrate the rich electronic properties, including the electrical conductivity, field-effect carrier mobility, and electroluminescence of highly crystalline 1D nanowire and coaxial donor-acceptor nanocable structures composed of elastic twist π-conjugated molecules. The electronic properties were measured using various techniques, including current-voltage (I-V), conducting-probe atomic force microscopy (CP-AFM), and space-charge-limited-current (SCLC) measurements. We prepared and characterized several electronic device structures, including organic field-effect transistors (OFETs) and organic light-emitting field-effect transistors (OLETs).

π‐Conjugated Donor Polymers: Structure Formation and Morphology in Solution, Bulk and Photovoltaic Blends

“…[25,35] Advances at the level of the theoretical description are summarized by Gierschner and Park in Ref. [36].…”

Effect of Methoxy Substitution on Supramolecular Arrangement of Borondifluorides of 2'-Hydroxy Chalcones and their Solid-State NIR Fluorescence

“…Substitution of π-conjugated systems with bulky side groups that hinder π-π cofacial stacking prevents aggregation-induced quenching, especially in the case of H-aggregation. Recently, restriction of intramolecular rotation and conformational planarization mechanisms was proposed as a chemical design strategy toward the generation of highly luminescent organic solids in which aggregation-induced emission (AIE) [9,10] or aggregation-induced enhanced emission (AIEE) [11] phenomena operate. In the case of BF2 complexes of 2'-hydroxychalcones and curcuminoids, we showed that NIR emission property is characteristic of tightly packed chromophores experiencing strong excitonic coupling.…”

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.…”