Optical Coumarins

Chemical properties of deposited monolayers have been studied in various ways. The degree of ionization of a substituted coumarin film deposited on quartz was determined as a function of the pH of a solution in contact with the film, from which comparison with Gouy-Chapman theory (see Section V-2) could be made [151]. Several studies have been made of the UV-induced polymerization of monolayers (as well as of multilayers) of diacetylene amphiphiles (see Refs. 168, 169). Excitation energy transfer has been observed in a mixed monolayer of donor and acceptor molecules in stearic acid [170]. Electrical properties have been of interest, particularly the possibility that a suitably asymmetric film might be a unidirectional conductor, that is, a rectifier (see Refs. 171, 172). Optical properties of interest include the ability to make planar optical waveguides of thick LB films [173, 174]. 

Recently, novel polymethine carbonyl-dyes based on coumarin moiety and their boron difluoride complexes 9a-d and lOa-d [34—36] were evaluated as fluorescent dyes for the detection of native proteins using bovine serum albumin (BSA) as a model protein, and as probes for the nonspecific detection of proteins using a BSA/ sodium dodecyl sulfate (SDS) mixture [37]. Optical properties of these compounds in the absence and presence of BSA, as well as in SDS and BSA/SDS mixture, were measured in Tris-HCl buffer (pH 8.0) (Table 1). 

While many commercial optical brighteners are trade secrets, most of these fluorescent compounds contain one or more ring systems and are derivatives of stilbene (Fig. 12.8.1), coumarin (Fig. 12.8.2), imidazole (Fig. 12.8.3), triazole... 

Fig. 19.13 (a) FRET between 0.2 mM Rhodamine B and 0.8 mM LD800. (b) Lasing of 2 mM LDS722 through cascade FRET from Coumarin 480 (0.2 mM) and R6G (0.4 mM). (c) Lasing of 0.125 mM Nile blue in methanol through FRET from 200 nM CdSe/ZnS core/shell QDs. The pump laser is at 485 nm. Reprinted from Ref. 18 with permission. 2008 Optical Society of... 

Reduction of coumarin in aqueous methanol, pH 5-6, in the presence of alkaloids yields an increased amount of dihydrocoumarin. Tliis is also the case for reduction of 4-methylcoumarin and now the 4-methyldihydrocoumarin isolated is optically active [137]. Tlie enantiomeric excess and yield of diliydrocompound both depend on the alkaloid used (Table 3.9) and Low concentrations of alkaloid are effective in achieving asynunetric induction. Concentrations of codeine above 4 mM do not further influence either the yield of dihydrocompound or the degree of induction. 

Examples of the optical pumping of solutions of luminescent conjugated polymers include laser action at 596 nm of poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) using excitation with 6 ns Nd YAG third harmonic pulses (354.7 nm). ° Tuning of hexane solutions of the co-polymer poly(2,2, 5,5 -tetraoctyl-p-terphenyl-4,4 -xylene-vinylene-p-phenylenevinylene) (TOP-PPV) was possible between 414 and 456 mn, similar to the classical coumarin laser dyes. ... 

Fig. 7 Selected 2PA spectra obtained by absolute fluorescence-based methods, a Spectra for fluorescein, rhodamine B, coumarin 307, and , -p-bis(o-methylstyryl)benzene (the solvent is indicated in the legend) obtained by Xu and Webb [78]. In the case of coumarin 307, the ordinate displays the quantity rjSy where rj is the fluorescence quantum yield, b Spectrum for , -p-bis(o-methylstyryl)benzene (this spectrum is obtained from the tabulated values for the band shape reported by Kennedy and Lytle [90] and the cross section at 585 nm reported by Fisher et al. [80], to correct for a typographical error in the 1986 paper). Part (a) reproduced with permission from [78]. 1996, Optical Society of America...

Hie dye-doped ORMOSIL materials exhibit much higher photostability than the reported polymer-doped materials. For example, optical gain was reported for several coumarin dyes in PMMA (13), It is significant to note that the best dyes reported could only be used to several hundred pulses and that most of the coumarin dyes could not even oscillate for 100 pulses. The ORMOSIL gels thus represent an improvement of at least 1-2 orders of magnitude in photostability. Optical gain was also reported for R6G doped into modified poly(methyl methacrylate) (14L These materials exhibited loss of 20% output after 180 pump pulses (1 J/cm ) at 532 nm. The reported plots indicate that these materials would have dropped by 90% after 275-300 pulses due to rapid steady state photodegradation once the pulse count exceeded the critical pulse number. In this case the R6G doped ORMOSIL gel laser offers a useful lifetime improvement by a factor of more than 15 over the reported polymer material. 

Applications of fiber-optic pH sensors in environmental analysis, biomedical research, medical monitoring, and industrial process control have been reviewed by Lin [67]. A multitude of luminescent systems for pH monitoring are commercially available, mostly under special trademarks. Pyrene [68-70], coumarin, bromothymol blue [71] and fluorescein [72-74] derivatives are typical examples that have been used in research in the past two decades. Carboxyfluorescein derivatives have been directly applied to skin tissue samples for the lifetime imaging of pH gradients in the extracellular matrix of the epidermis [75]. Two-photon excitation microscopy became an estab-... 

Further modification of the coumarin ring system in esculin (1) led to the development of 7-amino-4-methylcoumarins with an A-alkyl group at the 7-position. The sole representative of this series still on the market is 7-diethylamino-4-methylcoumarin (63) [91-44-1] [101], Despite its poor lightfastness, the good optical properties of this compound have kept it in use for the brightening of wool, cellulose acetate rayon, and polyamides. Compound 63 is produced by cyclocondensation of 3-diethylaminophenol with ethyl acetoacetate in the presence of zinc chloride [102],... 

When analogous treatment of AG is included, the two-sphere monopole or one-sphere dipole models predict a significant solvatochromic shift for optical ET of the CR type (i.e., in which the intial state is charge separated) e.g., a blue shift for absorption (e.g., betaine [48]) and a red shift for emission (e.g., coumarin [42]). Similar trends are typically found for CSh using the two-sphere model, while the one-sphere dipolar model is ambiguous, since it does not provide an adequate estimate of the polarity dependence of AG° [29],... 

The [2+2] photodimerization of coumarin has been extensively studied and previously reviewed in this series <1984CHEC>. An enantioselective variant of this transformation has recently been described <20050L1501>. Irradiation of coumarin or 6-methylcoumarin in the presence of an optically active host compound provided anti-head-to-head dimers with up to 98% ee (Equation 15). 

In a parallel synthesizer, electronically diverse libraries of more than 150 substituted coumarins 26 could be readily constructed in solution. Screening of the optical properties of the fluorophore ensemble gave rise to the identification of several library members with high fluorescence quantum yields (Fig. 5.10). 

Irradiation of 1 1 host-guest crystals of coumarin 85a with (/ ,/ )-(— )-6a derived from tartaric acid gave the (— )-antvdtedd-to-head dimer 86a of 96% ee [88]. Enantiospecific photodimerization of thiocoumarin 85b gave optically pure (+ )-anti-head-to-head dimer 86b when the 1 1 complex with R,R)- — )-6b was used. X-ray structure analysis revealed that the distance between the two ethylenic double bonds was short enough (3.59 and 3.42 A for 85a and 3.73 and 3.41 A for 85b) for addition to occur and topochemically [89]. Further, both reactions were found to proceed via a single crystal-to-single crystal transformation. 

Fluorescence quantum yields were determined using coumarin 540 in EtOAc as a reference. UV absorption maxima were determined in chloroform HOMO and LUMO values were determined by cyclic voltammetry in acetonitrile/tetrabutylam-monium fluoroborate solution. Optical and electrical properties of each derivative are provided in Table 1. 

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