Photophysics of Rose Bengal Incorporated into Polymers

MARTÍN MIRENDA; LELIA E. DICELIO; ENRIQUE SAN ROMÁN

La Plata, Buenos Aires, Argentina

Congreso; VIII Encuentro Latinoamericano de Fotoquímica y Fotobiología; 2004

Universidad de La Plata

PHOTOPHYSICS OF ROSE BENGAL INCORPORATED INTO POLYMERS     Martín Mirenda, Lelia E. Dicelio and Enrique San Román   INQUIMAE / DQIAyQF, FCEyN, UBA. Ciudad Universitaria, Pabellón II, C1428EHA Buenos Aires, Argentina. E-mail: martinm@qi.fcen.uba.ar   Keywords: Rose Bengal, polyelectrolytes, layer-by-layer assembly   One of the main objectives of our research on photoactive materials is the development of solid photosensitizers capable, for instance, of generating singlet oxygen efficiently. To improve their performance, the spatial distribution of dye molecules has to be controlled in order to reduce radiationless decay. Aggregation at high dye concentrations is the principal factor inducing deactivation of singlet states. As a way to control dye aggregation, electrostatic layer-by-layer assembly, which has been employed in the development of thin layer optical sensors[1] as well as in Förster energy transfer studies,[2] may be used to produce alternate layers of polyelectrolytes and a charged dye.As a preliminary step, we performed studies on the association between rose bengal (RB) and poly(diallyldimethylammonium chloride) (PDDA) in aqueous solution. In conditions where RB is monomeric in water, addition of PDDA promotes dye aggregation up to a ratio of RB molecules / PDDA units » 10-3. Further addition of PDDA reduces aggregation. In contrast, in a similar study on RB on positively charged nanoparticles[3] only dimeric species were found on the particle surface irrespective of the dilution extent. In other study[4] it was demonstrated that aggregation is reduced on adsorption of RB on a neutral surface. In both cases dimers were found to be fluorescent. Fluorescence experiments indicate that, at ratios lower than 10-3, simultaneously with a slow reduction of aggregation a very large increase in the fluorescence quantum yield takes place as PDDA is added. Furthermore, aggregates disappear when RB / PDDA are assembled on glass. Based on these results, conditions for the assemblage of PDDA including RB on activated glass surfaces, in a way that aggregation is minimized while maintaining a high local RB concentration, are discussed. [1]  S.-H. Lee, J. Kumar, S.K. Tripathy, Langmuir, 2000, 16, 10482-10489 [2] J. W. Baur, M. F. Rubner, J. R. Reynolds and S Kim. Langmuir., 1999, 15, 6460-6469 [3] M. E. Daraio and E. San Román. Helvetica Chimica Acta, 2001, 84, 2601-2614 [4] H. B. Rodríguez, M. G. Lagorio and E. San Román. Photochem. Photobiol. Sci., 2004, 3, in press