Fabrication and characterization of tetrapyrazinoindoloporphyrazine Langmuir-Blodgett Films

Abstract

Phthalocyanines are attractive due to their advantageous properties such as chemical and thermal stability, optical and electronic properties, and ordered crystal film growth. They have found potential applications in the field of organic light emitting diodes, organic field effect transistors, organic solar cells and sensors.[1] A large number of phthalcyanine derivatives have been synthesized to achieve specific properties. For instance, Peisert et al. reported that the ionization potential of phthalocyanine could be modified by changing the degree of fluorination.[2] It has been suggested that unsymmetrically substituted phthalocyanines with suitable donor and acceptor groups should exhibit second-order nonlinear optical responses.[3] Introduction of two nitrogen atoms into the equivalence of the 1,4-positions of the phthalocyanine benzene units leads to tetrapyrazinoporphyrazines. Owing to the additional nitrogen atoms, tetrapyrazinoporphyrazines are less electron-rich than the corresponding phthalocyanines. Tetrapyrazino[2,3-b]indoloporphyrazines have been synthesized by substituting an indole group at the 2,3 position of the pyrazine. (Figure 1) These molecules behave as push-pull intramolecular charge-transfer chromophoric systems in which the indole ring works as a donor group and the pyrazine ring as an acceptor group.[4] In this work, we have fabricated tetrapyrazino[2,3-b]indoloporphyrazine films using Langmuir-Blodgett (LB) technique and analyzed the films using X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS), electron loss spectroscopy (ELS), UV-vis spectroscopy, atomic force microscopy (AFM), and contact angle measurement.