Possible Formation of H-type Aggregates in H 2 TPyP/PMMA Guest Host Films
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1212-S11-17
Possible formation of H-type aggregates in H2TPyP/PMMA guest host films. W. S. Mota1, W. D. C. Melo2, L. A. O. Nunes3, A. E. H. Machado4, A. A. Batista5, I. Guedes2 and N. M. Barbosa Neto1 1
Instituto de Física – Universidade Federal de Uberlândia, CP 593, 38400-902 Uberlândia, MG, Brazil. 2
Departamento de Física – Universidade Federal do Ceará, CP 6030, 60455-970 Fortaleza, CE, Brazil. 3
Instituto de Física de São Carlos – Universidade de São Paulo, CP 369, 13560-970 São Carlos, SP, Brazil. 4
Instituto de Química – Universidade Federal de Uberlândia, CP 593, 38400-902 Uberlândia, MG, Brazil. 5
Departamento de Química – Universidade Federal de São Carlos, BR-13565-905 São Carlos, SP, Brazil.
ABSTRACT In this work we have employed UV-Vis absorbance and excitation techniques in addition to quantum chemical calculations to investigate the probable formation of H-type aggregates of zero charged aryl substituted porphyrin in a guest- host solid state structure. The films were factored via casting technique mixing free-base tetrapyridyl porphyrins (H2TPyP) and polymethilmethacrilate polymer (PMMA) chlorophorm solutions. A pathway for the possible formation of H-type aggregate is suggested.
INTRODUCTION Since molecular aggregates allow one the possibility of studying and understanding intermolecular interactions, increasing interest in its structure and formation dynamics has been verified in the past few decades [1-4]. Special attention has been given to the potential application of molecular aggregates in a series of electronic and optoelectronic devices [5-7]. Basically, there are two types of molecular aggregates: H- and J- type. H-type aggregates are formed by the face-to-face stacking of the molecules, while J-type aggregates are formed in an edge-to-edge configuration [8.9]. The formation of aggregates in water soluble porphyrins has extensively been investigated. This is due to the fact that porphyrin molecules are present in several fundamental natural processes, e.g., light harvesting [10] and electron and energy transport [11]. Understanding how the aggregate formation modify the photophysics properties of the monomer
is extremely important for applications in drug delivery systems [12] and photodynamic therapy against cancer [9,13]. Here we discuss on the possible formation of H-type aggregates of zero charged aryl substituted porphyrin in a guest host solid state structure. Films with different porphyrin concentrations, were factored by mixing free-base tetrapyridyl porphyrins (H2TPyP) and polymethilmethacrilate polymer (PMMA) chlorophorm solutions. The absorbance spectrum shows that the Soret band shifts upwards and broadens when the porphyrin concentration ranges from 0.08 up to 1.5 x 1016 molecules/cm3. For concentrations higher than ∼ 3 x 1016 molecules/cm3, we observed from the excitation spectrum the enhancement of a band at around 398 nm, which becomes more intense as the concentration increases. Quantum chemical calculations show that the shift results from the distortion of the
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