Luminescence in organized media and supramolecular interactions:physicochemical aspects and applications

Abstract

Introduction Molecular luminescence of analytes in organized media or in supramolecular complexes of cyclodextrinsThe photophysical and photochemical behaviour of molecules complexed to cyclodextrins (CD) is generally different from their behaviour in solution. The first observations in the field were qualitative and were related to the increased stabilisation of labile molecules, mostly drugs, against photodegradation when complexed to natural cyclodextrins [1]. Complexation by CD's was then the preferred subject for those involved in supramolecular chemistry and drug vectorisation techniques [2] as well as in separation techniques [3][4][5]. Stabilization of a molecule against photochemical degradation is still very important in the field of pharmaceutical sciences. A recent example is the stabilisation of promazine as an inclusion complex with β-cyclodextrin [6]. Other photochemists were attracted quite early to this field of research and initiated studies, which were mostly photophysical in nature [7,8]. The key observation was that the formation of supramolecular complexes of analytes with cyclodextrins (CDs) resulted in an increase of their fluorescence quantum yield or even in the appearance of room temperature phosphorescence (RTP) [9][10][11][12]. This enhancement has been used to increase the sensitivity and the selectivity in both luminescence and chromatographic techniques [13-15].We will not say more about RTP with CDs as the subject will be developed in another contribution in the same issue of this Journal. However RTP is also observed in the solubilization of analytes in micellar colloïdal solutions and this field will be reviewed hereunder.These properties have been used to develop analytical techniques, which combine the selectivity of complexation with an enhanced emission [16][17][18][19]. In this way an improvement in the detection limits is obtained in many separation techniques such as HPLC, capillary electrophoresis (CE) or planar chromatography. Furthermore these molecular interactions allow to reveal or to stabilize new molecular forms or to turn species which are normally non-emitting into luminescent ones. All these aspects are reviewed hereunder after a short summary on the nature of the intermolecular interactions, which lie at the heart of these effects. Nature of the interactions between an analyte and a CD or a micelleWithout going into a thorough analysis of the origin of the interactions which exist between molecules in dense media which concern us here, it seems useful to recall the most important factors which should be taken into account when any type of luminescence, fluorescence or phosphorescence is involved.

Solvolysis kinetic study and direct spectrofluorimetric analysis of the fungicide benomyl in natural waters

“…Moreover, a significant enhancement of the benomyl fluorescence signal was observed in aqueous micelle media and β-CD solutions, which appeared to be the most convenient media for analytical purposes. This behaviour was in agreement with data in the literature, which generally indicated an increase in the analyte solubility and fluorescence signal in these organised media [21][22][23][24][25]. In the case of kinetic curves with a plateau region, the t opt values in methanol, acetonitrile, 10 -4 M NaOH and neutral CTAOH solutions ranged between 15 and 100 min, depending on the particular medium (Table 1).…”

Luminescence methods for study and determination of pollutants in the environment

“…All these interesting properties of organized media, have been exploited to develop methods that can provide selectivity for extraction by complexation as well as sensitivity resulting from enhanced luminescence emission. Generally, lower LOD values have been obtained when using these organized media in separation techniques such as HPLC, capillary electrophoresis or planar chromatography [262].…”

Micelle‐enhanced spectrofluorimetric determination of diphenhydramine: application to human plasma and its simultaneous determination with naproxen in pharmaceutical tablets

“…Inclusion of drugs in cyclodextrin cavities or interaction of drugs with micelles, either with a charged head or hydrophobic core, may lead to fluorescence enhancement. [ 18 ] This enhancement may be attributed to increasing the rigidity of the fluorophore molecules, restricting their movement, and so decreasing energy transfer to the surrounding environment by nonradiative relaxation. As a result, the quantum yield is increased and the fluorescence intensity of the guest molecule is enhanced.…”

“…Several analytical methods have been reviewed for determination of NAP in formulations and biological matrices in analytical profile. [ 23 ] Other reported methods include spectrophotometry, [ 24–29 ] HPLC, [ 30–34 ] high performance thin layer chromatography (HPTLC), [ 29 ] spectrofluorimetry [ 3,5–39 ] and voltammetry. [ 40,41 ]…”