CONCENTRATION-MODULATED ABSORPTION SPECTROSCOPY AND THE TRIPLET STATE: SATURATION EFFECTS IN LONG-LIVED TRIPLETS

The theory and technique of the pump and probe method of Concentration Modulated Absorption Spectroscopy (COMAS) has been extended to species with high triplet yields. In the experiments erythrosin B and rose bengal have been applied as model compounds. Using continuous wave laser sources and a modulated pump beam the large COMAS signal expected from the formation of long-lived triplets is shown to be dramatically reduced as a result of strong saturation effects. A gain expression is derived which takes into account such saturation effects and which describes satisfactorily the interaction of coinciding focused Gaussian pump and probe beams with the sample solution. Based on this theory, singlet and triplet concentration profiles in the focal region in the sample can also be evaluated. Such a treatment will be of value in modelling the refractive index gradients that arise from the differing molecular polarisabilities of singlet and triplet molecular species and from the energy conversion of electronic excitation to heat

Szupramolekuláris rendszerek fotofizikai és fotokémiai tulajdonságai = Photophisical and photochemical properties of supramolecular systems

Fotoaktív vegyületek (olyan anyagok, amelyek alkalmazása optikai tulajdonságain alapul) tulajdonságait tanulmányoztuk oldatfázisban és szupramolekuláris komplexekben, UV-látható abszorpciós, fluoreszcencia és CD spektroszkópiai mérésekkel, továbbá időfelbontásos lézerspektroszkópiai kísérletekkel. Az eredményeket több esetben kvantumkémiai számítások alapján értelmeztük. Kutatásaink eredményeként - új modellt állítottunk fel fluoreszkáló kationos festékek orientációs relaxációjára oldatban, - fluoreszcens próbaként alkalmazható vegyületek gerjesztett elektronállapotait vizsgálva tisztáztuk a dezaktíválódási folyamatok mechanizmusát, - jellemeztük fémionok optikai kimutatására szolgáló szupramolekuláris receptorok ionmegkötésének szelektivítását, és királis ligandumok megkötésére szolgáló szupramolekuláris receptorok enantioszelektivítását, - tanulmányoztuk kationos festékek megkötődését több kötéshelyű szupramolekuláris receptorokon, párhuzamos reakciókból álló reakció-modelleket állítottunk fel és kiszámítottuk az egyensúlyi állandókat, - meghatároztuk a fotodinamikus terápiában (PDT) potenciálisan hatóanyagként alkalmazható ftalocianinoknak a PDT-s hatás szempontjából érdekes fotofizikai/fotokémiai jellemzőit. | Photoactive compounds have been studied in solution and in supramolecular complexes by UV-VIS absorption, fluorescence and CD spectroscopy and by time-resolved laser spectroscopic experiments. The results have been interpreted with help of quantum chemical calculations. As results of the project - a new model has been created to describe the orientational relaxation of fluorescent cationic dyes, - the decay mechanism of the excited electronic states of some fluorescent probes has been clarified, - equilibrium constants characterizing the selectivity of new metal ion binding supramolecular receptors and the enantioselectivity of new chiral supramolecular receptors have been determined, - the binding of cationic dyes on supramolecular receptors with multiple binding sites has been studied, the results have been interpreted in terms of reaction models with simultaneous reactions, - the photophysical/photochemical characteristics of new phtalocyanines relevant of their application in photodynamic therapy, have been determined

Spiropyran-based reversible, light-modulated sensing with reduced photofatigue

Switchable materials have tremendous potential for application in sensor development that could be applied to many fields. We are focusing on emerging area of wireless sensor networks due to the potential impact of this concept in society. Spiropyran-based sensors are probably the most studied type of photoswitchable sensing devices. They suffer from many issues but photofatigue, insufficient selectivity and lack of sensitivity are probably the most important characteristics that hinder their wider application. Here, we are address these issues and demonstrate that covalent attachment of modified spiropyran into a polymeric film significantly reduces photodegradation. The observed signal loss after 12th cycle of switching between the spiropyran and merocyanine forms is only about 27% compared to the loss of 57% of the initial signal in an equivalent experiment based on non-immobilized spiropyran. This has enabled us to demonstrate at least five reversible cycles of detection of an ion of interest (in our case H+) with minimal signal loss. Furthermore, we demonstrate that the sensitivity can be increased by incorporation of additional binding groups in the parent spiropyran molecule. Using molecular modelling to calculate the relevant bond lengths as a measure of interaction between MC and H+, the calculated increase of H-bond strength is approximately an order of magnitude for a derivative containing a methoxy group incorporated in the o-position of the parent spiropyran in comparison to the equivalent unsubstituted phenol. This theoretical result was found to correspond very well with experimental observation. As a result, we have increased the sensitivity to H+ by approximately one order of magnitude