Excitation Energy Transfer and Trapping in Dye-Loaded Materials: Modeling and Numerical Simulations of Concentration Self-Quenching

HERNÁN B. RODRÍGUEZ; ENRIQUE SAN ROMÁN

Villa Carlos Paz

Congreso; XIII Encuentro Latinoamericano de Fotoquímica y Fotobiología (XIII ELAFOT); 2017

Grupo Argentino de Fotobiología

Dye-loaded materials, such as thin films or bulk solids, have potential applications in photosensitization, photocatalysis, solar cells and fluorescence labelling. In order to maximize light absorption, high concentrations of dyes are desirable. However, at high concentrations the formation of molecular aggregates and statistical traps generally dissipate the excitation energy, lowering the excited states population. The design of highly absorbing systems, avoiding energy dissipation, requires the knowledge of the photophysical parameters governing concentration self-quenching. For that reason, modeling of excitation energy transfer and trapping processes in dye-loaded materials is mandatory to identify critical design parameters to avoid energy dissipation and to reach maximum efficiencies. As an attemp to describe the photophysical processes in highly concentrated dyed materials, in the present work some modeling strategies of concentration self-quenching, including theoretical calculations and numerical simulations of excitation energy transfer and trapping, are presented.As a first approximation, random distribution of dye molecules in two (2D) and three dimensions (3D) were considered. In the case of dyes with low aggregation tendency, Poisson statistics was used to asses the concentration of trapping centers, consistent in two or more dye molecules within a quenching radius, that show low interactions in the ground state but interact strongly in the excited state, leading to dissipation of the excitation energy. For 3D systems, theoretical calculations of energy migration and trapping rates, considering perfect, non-emitting traps, were performed using Loring, Andersen and Fayer (LAF) theory formalisms [1,2]. On the other hand, a Markovian matricial model was developed and numerical simulations of energy transfer and trapping were performed in 2D and 3D systems. While LAF theory is applicable for 3D random distributions of dye monomers and perfect traps, the Markovian matricial model allows numerical simulations of different dye distributions and system geometries and dimensionalities. However, depending on the complexity of the system considered, numerical simulations have a considerable computational cost. The comparison between LAF theory approach and numerical simulation predictions of concentration self-quenching will be presented, together with examples of the application of these models in the study of self-quenching in dyed materials [3-5]. Modeling aspects in the case of imperfect (emitting) traps will be also considered. [1] R. F. Loring, H. C. Andersen, M. D. Fayer, J. Chem. Phys. 1982, 76, 2015.[2] L. Kulak, C. Bojarski, Chem. Phys. 1995, 191, 67.[3] S. G. López, G. Worringer, H. B. Rodríguez, E. San Román, Phys. Chem. Chem. Phys. 2010, 12, 2246.[4] Y. Litman, H. B. Rodríguez, E. San Román, Photochem. Photobiol. Sci. 2016, 15, 80.[5] S. D. Ezquerra Riega, H. B. Rodríguez, E. San Román, Methods Appl. Fluoresc. 2017, 5, 014010.