Mono‐ and Di(dimethylamino)styryl‐Substituted Borondipyrromethene and Borondiindomethene Dyes with Intense Near‐Infrared Fluorescence

Abstract

Four novel borondipyrromethene (BDP) and -diindomethene (BDI) dyes with one or two (dimethylamino)styryl extensions at the chromophore were synthesized and spectroscopically investigated. An X-ray crystal structure shows that the extended auxochrome is virtually planar. All dyes thus display intense red/near infrared (NIR) absorption and emission. The (dimethylamino)styryl group induces a charge-transfer character that entails bright solvatochromic fluorescence, which is only quenched with increasing solvent polarity according to the energy-gap law. The dye with an additional dimethylanilino group at the meso position of BDP shows a remarkable switching of lipophilicity by protonation. Two dyes with an 8-hydroxyquinoline ligand at the meso position display quenched emission in the presence of Hg2+ or Al3+ owing to electron transfer from the excited BDP to the complexed receptor. The BDI dye presents a pH indicator with bright fluorescence and extremely low fluorescence anisotropy.

Two‐Photon Absorption‐Related Properties of Functionalized BODIPY Dyes in the Infrared Range up to Telecommunication Wavelengths

“…), or photonic therapeutic agents. [21][22][23][24][25][26] Great efforts have been recently devoted to shift their spectroscopic properties to the NIR spectral range by i) introduction of electrondonating moieties, [27] ii) rigidification of the structure, [28] or iii) replacement of the meso-carbon by a nitrogen atom (the ''aza''-Bodipy). [29][30][31] But surprisingly, whereas water-soluble conventional Bodipy dyes featuring low two-photon cross-sections were used for two-photon imaging microscopy, [32,33] these compounds were not fully optimized for TPA applications.…”

On the Signalling Pathways and CuII‐Mediated Anion Indication of N‐meso‐Substituted Heptamethine Cyanine Dyes

“…Fluorescence experiments were performed with a 908 standard geometry, with polarisers set at 54.78 for emission and 08 for excitation. The fluorescence quantum yields (F f ) of 1-3 were determined relative to cryptocyanine in ethanol (F f = 0.014 AE 0.001) [5] and oxazine I in ethanol (F f = 0.152 AE 0.002). For 4 and 5, the fluorescence quantum yields were determined relative to IR-125 in dimethylsulfoxide (F f = 0.22 AE 0.01).…”

“…For details, see ref. [5]. The uncertainties of measurement were determined to AE 5 % (for F f > 0.2), AE 10 % (for 0.2 > F f > 0.02) and AE 20 % (for 0.02 > F f ).…”

“…(4)]. However, due to the intrinsic assumptions of the empirical Hill analysis, K a data derived for systems showing non-integer Hill coefficients, like n = 0.93 here, are only a poor measure of affinity [60] and cannot be directly compared with, for instance, binding constants obtained for a conventional equilibrium of a chemical indicator such as that in Equation (5). A more useful parameter is the socalled half-saturation value, K 0.5 , derived for Y = 0.5 [see Eq.…”

“…[2] Two of the main advantages of operating in the NIR region are the virtually negligible background absorption and autofluorescence. [3] Since it is difficult to realise high fluorescence quantum yields in this spectral region because the lowering of the energy gap between the excited and ground states intrinsically leads to enhanced internal conversion according to the energy-gap rule, [4,5] there is an intense search for potent NIR fluorophores. [6] On the other hand, most NIR dyes show intense absorption bands because their chromophores are characterised by a highly conjugated and often largely extended p-electron system.…”