Synthesis, Photophysical and Electrochemical Properties of Bis‐Squaraine Dyes Fused on Isomeric Benzodipyrrole Central Units

Abstract

Exciton interactions are not only observed in assembled molecules but also in compounds with multiple chromophores referred to as superchromophores. We have developed isomeric bis-squaraine dyes as superchromophores in which two squaraine chromophores are fused onto the isomeric benzodipyrrole skeleton so as to regulate conformations and to reduce distances between two chromophores. The dyes with benzo[1,2-b:3,4-b']dipyrrole and benzo[1,2-b:5,4-b']dipyrrole moieties exhibited split electronic absorption originated from the intramolecular exciton inter-action. The intensity of the split absorption bands varies in correlation with the orientation of chromophores. The isomeric dye with benzo[1,2-b:4,5-b']dipyrrole moiety exhibited a near-infrared absorption associated with the resonance throughout two chromophores. Their electrochemical and spectroelectrochemical properties are distinct from those of monomeric dyes owing to electronic interactions between the two chromophores. Thus, the structural isomerism of the central skeleton significantly affects their optical properties as well as their electrochemical properties.

Modulating Energy Transfer and Light‐Emitting Colors by Chiral Dye Exchange and Achiral‐to‐Chiral Dye Conversion

“…Dichloromethane solution of exo‐ 2 shows light‐emitting color coordinates (0.16, 0.04) in CIE 1931 Chromaticity diagram, which falls into the deep blue regain [(CIE ( x , y )<(0.17, 0.09)]. The deep blue emission has recently attracted much interest for practical applications [30–33] . Compared with solution emission, singe crystal of exo ‐ 2 shows a large red shift from 376 nm to 471 nm in emission wavelength, and loses fine emission structure.…”

“…The deep blue emission has recently attracted much interest for practical applications. [30][31][32][33] Com- Table 1. Optical data of dyes exo-2 and exo-3 in dichloromethane (c = 1 × 10 À 5 M) and single crystal of exo-2: absorption maximum wavelength (λ A ), extinction coefficient (ɛ), emission maximum wavelength (λ F ), fluorescence quantum yield (Φ), and full width at half maximum (FWHM).…”

Chiroptical Properties of Planar Benzobisthiazole-Bridged Squaraine Dimers

“…64−66 Following this concept, we have recently investigated axially chiral squaraines with outstanding chiroptical properties, where an analysis of the contributing terms of eq 2 confirmed the dominance of R ex , but also revealed a significant contribution of the electric− magnetic coupling between the monomers to the overall rotational strengths. 67 In order to enhance the electric−magnetic contribution, in this work, we designed squaraine dimers with a planar, and thereby non-chiral, rigid heterocyclic linkage 51,68 where R ex should be minimal but where R e−m is enhanced because of optimal angles between μ 1 and m 2 . The five target molecules investigated in this work are shown in Figure 1.…”

“…In order to enhance the electric–magnetic contribution, in this work, we designed squaraine dimers with a planar, and thereby non-chiral, rigid heterocyclic linkage , where R ex should be minimal but where R e–m is enhanced because of optimal angles between μ 1 and m 2 . The five target molecules investigated in this work are shown in Figure .…”

Squaraine Appended with Benzodipyrrole for Fluorescent Sensing of Methanol: Exciton Coupling Controls Photophysical Properties

“…Our recent study explored the distinctive absorption and redox properties of squaraine dimers that incorporate a benzodipyrrole moiety as the central scaffold [31] . These dimers are composed of two chromophores fused at the central benzene ring, with a fixed orientation, as illustrated in Figure 2.…”