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

Abstract

The excited‐state behavior of four‐coordinate N,C‐chelate organoboron dyes, based on arylisoquinoline ligands with varying degree of charge‐transfer character, was characterized. Data related to excited triplet state formation, oxygen quenching, and singlet‐oxygen formation were obtained. The results jointly rationalize the previously observed high photostability of the dyes in air‐equilibrated media. Furthermore, femtosecond transient absorption experiments enabled the spectroscopic visualization of the excited intramolecular charge transfer (ICT) state that gives rise to the fluorescence of the dyes.

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

“…[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.…”

“…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) .…”

“…20 nm below 500 nm. Using an isoquinoline fragment instead of a pyridine, the charge‐transfer properties of the dyes become more pronounced, as we have shown for related BAI dyes. In order to explore the possibility to combine the charge‐transfer features with the observation of spectrally tunable CPL emission, we have prepared new members of the BAI dye platform that contain a shielding phenyl ring at the 8‐position of the naphthyl moiety (see Figure ).…”

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

“…The photophysical characterization of the dyes 16 – 19 was completed by nanosecond laser-flash photolysis experiments in acetonitrile [45]. The laser excitation (λ exc = 308 nm) of the dyes 16 and 17 in nitrogen-purged solution yielded transient absorption spectra with a broad band at λ max = 610 and 600 nm, respectively (see Fig.…”

Recent Advances in π-Conjugated N^C-Chelate Organoboron Materials

“…NˆC-chelate organoboron dyes, including those with arylisoquinoline ligands (19-20, Figure 11), display high stability in air-equilibrated media, and an excited state intramolecular charge-transfer (ICT) character leading to high Stokes shifts, solvatofluorochromic behavior, and high photochemical stability [60,61]. Pischel and coworkers [61] found that the π-extended system 20a-c (Figure 11) exhibits unique two-photon absorption (TPA) properties in the NIR region.…”