Red-Emitting Tetracoordinate Organoboron Chelates: Synthesis, Photophysical Properties, and Fluorescence Microscopy

Abstract

Seven tetracoordinate organoboron fluorophores with heterobiaryl N,O- or N,N-chelate ligands were prepared and photophysically characterized (in toluene). The electronic variation of the heteroaromatic moiety provided a means for the fine-tuning of the UV/vis absorption and emission spectra. In the most interesting cases, the spectra were red-shifted to maximum absorbance at wavelengths longer than 500 nm and emission maxima between 620 and 660 nm. The pronounced intramolecular charge-transfer character of the dyes yielded large Stokes shifts (3500-5100 cm), while maintaining appreciable fluorescence quantum yields of up to 0.2 for emission maxima longer than 600 nm. The lipophilic character of the dyes enabled their application as stains of vesicle substructures in confocal fluorescence microscopy imaging.

Azabora[5]helicene Charge‐Transfer Dyes Show Efficient and Spectrally Variable Circularly Polarized Luminescence

“…The stronger electron‐donating ‐NMe 2 shifts the emission maximum even close to 600 nm. These new BAI dyes usefully complement a previously investigated series of racemic BAI dyes with demonstrated applications in bioimaging . Further, this work provides an attractive path for the design of spectrally fine‐tuned emission of CPL‐SOM architectures …”

“…Much effort has been dedicated to the development of synthetically flexible platforms which enable the photophysical fine‐tuning of the dyes . As part of our own research program we have developed borylated arylisoquinoline (BAI) dyes, which in their N,C‐chelate variant are strongly emitting, solvatochromic, and two‐photon‐absorbing charge‐transfer fluorophores with application potential in bioimaging . With the idea to further enrich the photophysics of this fascinating platform we have built on their biaryl structure, which provides a means to arrive at dyes with helical chirality and the corresponding observation of interesting chiroptical properties, including the detection of circularly polarized luminescence (CPL) .…”

“…Four-coordinate organoboron chelates [1][2][3] are attractive targets for the design of photostable fluorescent dyes for the most varied applications,i ncluding bioimaging, [4][5][6][7][8][9][10][11][12] sensing, [13][14][15][16][17] and organic light-emitting diodes. [18] Much effort has been dedicated to the development of synthetically flexible platforms which enablet he photophysical fine-tuning of the dyes.…”

“…[3,[9][10][11][19][20][21][22][23][24][25][26][27] As parto fo ur own research program we have developed borylated arylisoquinoline (BAI) dyes,w hich in their N,C-chelate variant are strongly emitting, solvatochromic, and two-photon-absorbing charge-transfer fluorophores with applicationp otentiali nb ioimaging. [9,10,28] With the idea to further enricht he photophysicso ft his fascinating platform we have built on their biaryl structure,w hich providesameanst oa rrive at dyes with helical chirality and the correspondingo bservation of interesting chiropticalp roperties, including the detection of circularly polarized luminescence (CPL). [29][30][31][32] The phenomenoni sw ell established for supramolecular assemblies or nanostructures.…”

Excited‐State Pathways of Four‐Coordinate N,C‐Chelate Organoboron Dyes

“…As part of our research program we have been interested in arylisoquinolines as chelate ligands for organoboron dyes (BAI dyes) with specific focus on their appropriateness for bioimaging with confocal or multiphoton fluorescence microscopy . In a recent work we have demonstrated that four‐coordinate N,C‐chelate dyes such as the ones shown in Figure (dye 1 – 4 ) are interesting candidates for these applications .…”