Nanocomposites and nanomaterials

Features of cyanine dyes aggregation in TiO2 matrices 
Pisklova P.V., Ropakova I.Yu., Bespalova I.I., Yefimova S.L., Sorokin A.V. 
Yu.V. Malyukin Nanostructured Materials Department,
Institute for Scintillation Materials of NAS of Ukraine
60 Nauky Ave., Kharkiv, 61072, Ukraine
E-mail: polinkapisklova@gmail.com

Under certain conditions, the molecules of some dyes and pigments can form highly ordered structures (molecule aggregates). Due to the translational symmetry of molecules within such aggregates (J-aggregates, named by their discoverer E. Jelley), the electronic excitations of individual molecules are delocalized over the segments of aggregate chains with the formation of Frenkel exciton. The excitonic nature of electronic excitations leads to unique optical properties of aggregates, which depend on the structure of aggregates and their microenvironment. For example, depending on the arrangement of molecules in the chain, the excitonic band can be narrow intense red-shifted (J-band), or a broad blue-shifted (H-band). 
An urgent task is to create solid samples of J-aggregates that have a higher photo- and physical stability compared to solutions. Thus, they are prospective for various applications. Such samples can be obtained, for example, in the form of polymer films or porous matrices. 
There are a sufficient number of works devoted to the study of dyes in nanoporous matrices can be found in the literature. Our group has already studied the aggregation of dyes in AAO matrices, which differ significantly in structure from TiO2 matrices. 
Currently, titanium dioxide-based materials are widely studied and used because of their unique properties. TiO2 is an inexpensive, environmentally friendly material, widespread in nature, resistant to UV radiation. It possesses semiconducting properties and, upon absorption of a quantum of electromagnetic radiation, is capable of generating a pair of charges "electron-hole" [1]. 
This report aims to demonstrate the features of several cyanine dyes aggregation within titanium dioxide matrices as separate or combined thin films. It has been revealed, that depending on the charge of the TiO2 matrices, aggregates of different types could be formed. It has been shown, that using the different dye combination the optical response of the sample can be improved.

1.	Song X. M. A dual-layer titania film with enhanced photocatalytic activity // Journal of Physical Chemistry C.-2009.-113.-P. 10681-10688.