Preparation of Near‐Infrared Emissive π‐Conjugated Polymer Films Based on Boron‐Fused Azobenzene Complexes with Perpendicularly Protruded Aryl Substituents

Abstract

Most organic luminescent dyes usually show poor emission in solid due to aggregation‐caused quenching due to nonspecific intermolecular interaction, such as π–π stacking. Furthermore, since commodity molecules having near‐infrared (NIR) emission properties tend to have extended π‐conjugated systems, development of luminescent organic materials with solid‐state NIR emission has been still challenging. Herein, the series of the azobenzene complexes with the perpendicularly‐protruded aryl derivative at the boron atom toward π‐conjugated system is synthesized. From the optical measurements, it is shown that these complexes can show crystallization‐induced emission enhancement behaviors. The donor–acceptor type π‐conjugated polymers composed of the azobenzene complexes are also synthesized. Highly‐efficient NIR emission from the phenyl‐substituted polymers both in solution (λPL = 742 nm, ΦPL = 15%) and film states (λPL = 793 nm, ΦPL = 9%) is obtained. Furthermore, emission wavelengths can be tuned by changing the substituent at the boron atom to the modified aryl groups. From mechanistic studies including theoretical calculations, it is shown that electronic interaction is allowable between the aryl substituent to the π‐conjugated system through the tetradentate boron.

Vapochromic Luminescent π‐Conjugated Systems with Reversible Coordination‐Number Control of Hypervalent Tin(IV)‐Fused Azobenzene Complexes

“…[28][29][30] As examples, we discovered cubic silica and boron cluster compounds named polyhedral oligomeric silsesquioxane (POSS) [31,32] and ocarborane, [33,34] respectively, have been applicable to main scaffolds for creating functional materials showing superior luminescence behaviors with high durability or stimuli-responsiveness. We recently reported the series of solid-state luminescent complexes and polymers containing boron-fused azomethine (À C=NÀ ) [35][36][37][38][39] and azo (À N=NÀ ) [40][41][42][43][44] complexes with the tridentate ligands, o-salicylideneaminophenol or 2,2'-dihydroxyazobenzne scaffold, respectively. [45] These materials showed intense emission in the condensed state, and highlyefficient polymer film emission [38] and near-infrared (NIR) absorptive and emissive characteristics [40][41][42]44] were obtained.…”

“…We recently reported the series of solid-state luminescent complexes and polymers containing boron-fused azomethine (À C=NÀ ) [35][36][37][38][39] and azo (À N=NÀ ) [40][41][42][43][44] complexes with the tridentate ligands, o-salicylideneaminophenol or 2,2'-dihydroxyazobenzne scaffold, respectively. [45] These materials showed intense emission in the condensed state, and highlyefficient polymer film emission [38] and near-infrared (NIR) absorptive and emissive characteristics [40][41][42]44] were obtained. It should be emphasized that unique environment-sensitive luminescent properties, such as aggregation-induced emission (AIE), [46,47] crystallization-induced emission enhancement (CIEE), [48] in which enhanced emission can be observed only in aggregation and crystal, respectively.…”

Discovery of Functional Luminescence Properties Based on Flexible and Bendable Boron‐Fused Azomethine/Azobenzene Complexes with O,N,O‐Type Tridentate Ligands

“…Next, we focused on the substituent effect on the perpendicularly‐protruded substituent at the boron atom [87] . Most of organic luminophores usually show poor emission in the solid state due to ACQ caused by non‐specific intermolecular interaction, such as π–π stacking [49] .…”

Controlling Energy Gaps of π‐Conjugated Polymers by Multi‐Fluorinated Boron‐Fused Azobenzene Acceptors for Highly Efficient Near‐Infrared Emission

“…In the films, the BAz polymers also showed emission in the NIR region (Figure 2D and Table 1). P‐BAz showed intense emission even in the film ( λ PL =858 nm, Φ PL =4%) [11b,e] . Although the other polymers exhibited weak emission ( Φ PL <1%), however the λ PL s were detectable at 916∼980 nm.…”

“…In the case of P‐BAz‐5F and P‐BAz‐35F , high molecular weight polymers were fractionated by high performance liquid chromatography (HPLC) in chloroform as an eluent. In this research, the synthetic polymer data of P‐BAz were cited or recollected as comparison [11b,d,e] . All synthesized compounds showed good solubility in common organic solvents such as toluene, chloroform, dichloromethane and tetrahydrofuran, and can be characterized by 1 H, 13 C, 11 B NMR, MS spectra (see Supporting Information).…”