Boradipyrromethenecyanines

Abstract

A series of meso-polymethine-substituted BODIPY compounds have been synthesized by the reaction of mesomethyl-3,5-diphenylboradipyrromethene with a number of hemicyanine derivatives. The dyes obtained exhibit intense long-wavelength absorption, but weak fluorescence. Upon protonation of the dyes the long-wavelength band disappears and the intensity of the short-wavelength band in- IntroductionBoradipyrromethene dyes (4,4-difluoro-4-bora-3a,4a-diazas-indacenes, BODIPY, BDP) have attracted considerable attention over the past two decades. The ever increasing interest in this type of compound is due to their excellent thermal, chemical, and photochemical stability, high molar absorptivity, high fluorescence quantum yields, insensitivity to solvent polarity and pH, long excited-state lifetimes, a large two-photon cross-section for multiphoton excitation, lack of ionic charge, and good solubility.[1] However, the absorption maxima of the majority of BODIPYs are below 600 nm. Long-wavelength dyes are important for both basic and applied research [2] and therefore many synthetic approaches exist for modifying the BODIPY core to give structures that absorb at longer wavelengths. One of the most promising approaches to the modification of BOD-IPY is its peripheral functionalization with conjugated chromophores. Scheme 1.[a] Institute of Organic Chemistry, National Academy For example, distyryl-substituted derivatives A exhibit a bathochromic shift of the absorption maximum of 79 nm compared with diphenyl-substituted analogues (see Scheme 1). The bathochromic shift of phenylethynyl analogues B is somewhat smaller, however, both A and B are typical BODIPYs and demonstrate high fluorescence quantum yields that are fairly insensitive to the nature of the solvent.[3] The introduction of additional 4-(dialkylamino) substituents into A (structure C [4] ) results in even more pronounced spectral changes, with bathochromic shifts of around 80 nm. The structures C exhibit very small solvatochromism and considerable positive solvatofluorochromism. The fluorescence intensity increases significantly with decreasing solvent polarity. Protonation of the dialkylamino groups in C leads to optical properties that are very similar to those of A. Although the charge-separated mesomeric form C2 is typical of merocyanine dyes, the properties of the structures C (e.g., easy protonation, weak solvatochromism, and relatively low molar absorptivity) as a whole do not correspond to those of merocyanines. Thus, the dialkylamino groups in structures C provide considerable spectral changes, but do not change the color of the V. P. Yakubovskyi, M. P. Shandura, Y. P. Kovtun FULL PAPER BODIPY core. Therefore in this case they cannot be referred to as true "end groups" as defined in the ideology of polymethine dyes.This statement is even more evident for structures D. [3a,4b,5] In this case the dialkylamino group leads to a small hypsochromic shift of the BODIPY absorption maximum. The fluorescence quantum yields are quenched in polar solvents but not i...

Molecular design of near infrared polymethine dyes: A review

“…Gerasev et al [155][156][157] for the anionic polymethine dyes 4. Combined quantum-chemical and spectral studies of the dyes 4 [85][86][87] have shown that two lowest electron transitions are split transitions, involving two low positioned acceptor levels, in contrast to the cationic cyanine dyes where two lowest transitions are connected with two split donor levels.…”

Synthesis and Supramolecular Functional Assemblies of Ratiometric pH Probes

“…BODIPY dyes are relativelyeasy to synthesise in high yield and multi-gram quantity,a nd their excellent spectroscopic/photophysical properties can be easily tuned by introducing different electron-releasing/-withdrawing groups into the BODIPY core. [12] The simple synthetic approach towards the BODIPY core is mainly based on porphyrin chemistry,w hich involves the acidcatalysed condensation of pyrrole (40)d erivatives with aldehydes (41;F igure 10). [12] Oxidation of the resulting dipyrromethane under mild conditions (i.e.,D DQ) affords the dipyrromethene (42), whichi sc omplexed with boron trifluoride in basic media to give rise to the boron difluoride complex (43).…”

“…Alternatively, asymmetric BODIPY dyes (47)c an be prepared by sequentialc ondensation of derivatives of 40 with activated carboxylic acids (i.e., 44)o ra cid anhydrides [39] or orthoesters. [40] Isolation of the corresponding acylpyrrole (45)a llows access to asymmetricd ipyrrins, which, again, can be treated with an excess of base andb oron trifluoride etheratet oy ield final BODIPY 47.At hird strategy involves the self-condensation of acetylated pyrrole-2-carbaldehyde (48)p romoted by phosphorus oxychloride to obtain dipyrromethene (49), whichc an be furtherf unctionalised to give rise to BODIPY 50 in high yields after simplec hromatographic purification ( Figure 10). [41] BODI-PYs are hydrophobic and robust probes that allow many postsynthetic modifications on the meso-aryl substituent, such as oxidation, reduction and nucleophilica romatic substitution, withoutsignificantd ecomposition of the dye.…”

“…[12] The BODIPY scaffold has been widely exploited in pH fluorescent probes [44] and in numerouse xamples for other analytes. [11,40] BODIPY derivatives with hydroxyl groups (51)(52)(53)h ave been reported as fluorescent probes for pH sensing in aqueous and mixed aqueous-organic media( Figure 11). [45] However,n ot all of these molecules are suitable for intracellular pH measurements.…”

<strong>Exploring BODIPY <em>meso</em>-enamines as singlet-oxygen photosensitizers for PDT</strong>

“…These transamination reactivity of dimethylamino-based enanamines, [16] allowed extending the study series by the preparation of enamine 3, which was straightforwardly obtained by treating 2a with 4-nitroaniline in presence of acetic acid and dichloromethane (DCM) as the solvent (Scheme 2). Scheme 2.…”