Squaraine-derived rotaxanes: highly stable, fluorescent near-IR dyes

Squaraines are fluorescent, near-IR dyes with promising photophysical properties for biomedical applications. A limitation with these dyes is their inherent reactivity with nucleophiles, which leads to loss of the chromophore. Another drawback is their tendency to form nonfluorescent aggregates in water. Both problems can be greatly attenuated by encapsulating the dye inside an amide-containing macrocycle. In other words, the squaraine becomes the thread component in a Leigh-type rotaxane, a permanently interlocked molecule. Two new rotaxanes are described: an analogue with four tri(ethyleneoxy) chains on the squaraine to enhance water solubility, and a rotaxane that has an encapsulating macrocycle with transposed carbonyl groups. An X-ray crystal structure of the latter rotaxane shows that the macrocycle provides only partial protection of the electrophilic cyclobutene core of the squaraine thread. The stabilities of each compound in various solvents, including serum, were compared with a commercially available cyanine dye. The squaraine rotaxane architecture is remarkably resistant to chemical and photochemical degradation, and likely to be very useful as a versatile fluorescent scaffold for constructing various types of highly stable, near-IR imaging probes.     

Synthesis of near-IR fluorescent oxazine dyes with esterase-labile sulfonate esters

Near-IR oxazine dyes are reported that contain sulfonate esters which are rapidly cleaved by esterase activity to unmask highly polar anionic sulfonates. Strategies for the synthesis of these dyes included the development of milder dye condensation conditions with improved functional compatibility and the use of an alkyl halide that allows for the introduction of esterase-labile sulfonates without the need for sulfonation of the target molecule.     

Chemistry at boron: synthesis and properties of red to near-IR fluorescent dyes based on boron-substituted diisoindolomethene frameworks

A general method for the synthesis of difluorobora-diisoindolomethene dyes with phenyl, p-anisole, or ethyl-thiophene substituents has been developed. The nature of the substituents allows modulation of the fluorescence from 650 to 780 nm. Replacement of the fluoro ligands by ethynyl-aryl or ethyl residues is facile using Grignard reagents. Several X-ray molecular structures have been determined, allowing establishment of structure-fluorescence relationships. When the steric crowding around the boron center is severe, the aromatic substituents α to the diisoindolomethene nitrogens are twisted out of coplanarity, and hypsochromic shifts are observed in the absorption and emission spectra. This shift reached 91 nm with ethyl substituents compared to fluoro groups. When ethynyl linkers are used, the core remains flat, and a bathochromic shift is observed. All the fluorophores exhibit relatively high quantum yields for emitters in the 650-800 nm region. When perylene or pyrene residues are connected to the dyes, almost quantitative energy transfer from them to the dye core occurs, providing large virtual Stokes shifts spanning from 8000 to 13,000 cm(-1) depending on the nature of the dye. All the dyes are redox active, providing the Bodipy radical cation and anion in a reversible manner. Stepwise reduction or oxidation to the dication and dianion is feasible at higher potentials. We contend that the present work paves the way for the development of a new generation of stable, functionalized luminophores for bioanalytical applications.     

Water-soluble, deep-red fluorescent squaraine rotaxanes

Eight fluorescent squaraine rotaxanes with deep-red absorption/emission wavelengths were prepared and assessed for chemical stability and suitability as water-soluble, fluorescent tracers. The most stable squaraine rotaxanes have four large stopper groups attached to the ends of the encapsulated squaraine, and two members of this structural class have promise as highly fluorescent tracers with rapid renal clearance and very low tissue uptake in living mice.     

Photoisomerization of sterically hindered polymethine dyes

Conclusions In sterically hindered polymethine dyes the photoisomerization process, with the formation of sterically hindered trans and di-cis forms, successfully competes with the nonradiative degradation of the energy on the higher vibrational sublevels of the ground state.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1926–1930, August, 1977.     

Photolysis of sterically protected bicyclic 1,2,3-selenadiazole

The photolysis of sterically protected 1,2,3-selenadiazole in the presence of olefin was studied. The regioselective cycloadducts were obtained via the initially formed zwitter-ionic intermediate.     

Simple and efficient preparation of sterically protected 1,4-diphosphafulvenes

A new synthetic method for sterically protected 1,4-diphosphafulvenes (2-methylene-2,3-dihydro-1H-[1,3]diphospholes) has been developed starting from (arylethynyl)phosphines and ca. 0.25 molar amount of butyllithium. The catalytic mechanism of the reaction is discussed based on the results of deuterium-labelling experiments.     

Reactions of sterically protected phosphaalkenes with some boron reagents

The reactions of sterically protected phosphaalkenes with some boron reagents, such as boron hydrides, were carried out leading to hydroboration products depending on the substrates and boron reagents. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 187–196, 1999     

Aza-boron-dipyrromethene dyes: TD-DFT benchmarks, spectral analysis and design of original near-IR structures

The excited-state energies of aza-boron-dipyrromethene (Aza-BODIPY) derivatives are investigated with Time-Dependent Density Functional Theory (TD-DFT), with twin goals. On the one hand, a pragmatic, yet efficient, computational protocol is defined in order to reach rapidly semi-quantitative estimates of the λ(max) of these challenging dyes. It turned out that a PCM-TD-BMK/6-311+G(2d,p)//PCM-PBE0/6-311G(2d,p) approach delivers appropriate lower bounds of the experimental results, despite the inherent limits of the vertical approximation. On the other hand, the method is applied to design new dyes absorbing in the near-IR. The spectral features of ca. 30 new compounds have been simulated in a systematic way, trying to efficiently combine several available synthetic strategies leading to significant bathochromic displacements. A series of dyes absorbing above 850 nm are proposed, illustrating that (relatively) fast theoretical calculations might be a useful pre-screening step preceding synthesis.     

Axially chiral bichromophoric fluorescent dyes

A new life for Kurt Mislow's authentic amines: Diaminobiphenyls were applied as the framework materials for the synthesis of axially chiral bichromophoric systems with strong CD and CPL effects.     

Formation and structural characterization of a sterically protected silicic acid diester

The hydrolytic stability of the sterically protected dichlorosilane (Mes*? O)₂SiCl₂ was investigated. The resulting products have been identified by electrospray mass spectrometry and, in the case of (Mes*? O)₂Si(OH)₂, the crystal structure was obtained. Copyright © 2005 John Wiley & Sons, Ltd.     

The chemistry of fluorescent bodipy dyes: versatility unsurpassed

The world of organic luminophores has been confined for a long time to fairly standard biological labeling applications and to certain analytical tests. Recently, however, the field has undergone a major change of direction, driven by the dual needs to develop novel organic electronic materials and to fuel the rapidly emerging nanotechnologies. Among the many diverse fluorescent molecules, the Bodipy family, first developed as luminescent tags and laser dyes, has become a cornerstone for these new applications. The near future looks extremely bright for "porphyrin's little sister".     

Spectroscopic studies of fluorescent perylene dyes

The lowest electronic transition of the fluorescent perylene dye bis-(3,5-di-tertbutylphenyl)-perylene-3, 4:9,10-biscarboximide has been investigated b     

Cell-permeable iminocoumarine-based fluorescent dyes for mitochondria

A class of small molecule fluorophores, 2-iminocoumarin-3-carboxamide derivatives, has been developed by a rapid microwave-assisted process. These fluorescent probes are cell membrane permeable with low cytotoxicity and able to selectively stain organelles in living cells.     

Rotational barriers in perylene fluorescent dyes

Rotational barriers in N-substituted perylene dyes have been determined. Phenyl substituents with tert-butyl groups in the o-position give rigid systems, whereas secondary alkyl groups cause low rotational barriers. In spite of that, fluorescent quantum yields are high in both cases. Conformations in solution are discussed.     

Isolation and characterization of some very stable 1-phospha-allenes: sterically protected iminomethylene- and ethenylidenephosphines

Very stable iminomethylenephosphine (3) and ethenylidenephosphine (4) were obtained by steric protection with the 2,4,6-tri-tertbutylphenyl group and some of the spectroscopic data are described.