Formation of J-aggregates in Langmuir-Blodgett films: Effect of stearic acid and nano clay platelets

ABSTRACT

In the present communication, a water soluble prophyrin derivative, tetra-cationic dye 5, 10, 15, 20-tetrakis (1-methyl-4-pyrindino) porphyrin tetra (p-toluenesulfonate) (abbreviated as TMPyP) has been used to prepare stable Langmuir monolayer at the air–water interface by allowing it to adsorb from the aqueous subphase, into the preformed Langmuir monolayer of anionic stearic acid (SA) and cationic octadecylamine (ODA). Anionic nano clay platelets Laponite acted as mediator to initiate adsorption of cationic TMPyP into the cationic ODA monolayer. Surface pressure versus area per molecule (π-A) isotherm studies of SA-TMPyP complex monolayer gave valuable information about the TMPyP molecular area. Organizations of TMPyP molecules were greatly affected in the two different kinds of anionic and cationic matrices. Adsorption led to the flattening of TMPyP molecules in both the matrices. The organization of TMPyP tagged nano clay platelets in preferred direction led to the development of J-band resulting due to the formation J-aggregates in the Langmuir-Blodgett (LB) films. This has been confirmed by UV-vis absorption spectroscopic studies.

KEYWORDS:

• AFM
• isotherm studies
• j-aggregates
• langmuir-blodgett films
• molecular area

Acknowledgments

Dr. S. A. Hussain is grateful to DST for financial support through DST Project (Ref. No. MR/2014/000234; dated 17.03.2015). The authors also acknowledge the financial support under FIST Program – 2014 (Ref. SR/FST/PSI-191/2014 dated 21.11.2014). Mr. Chandan Debnath is grateful to UGC-NERO for financial support through UGC project (Ref. No. F.5-378/2014-15/MRP/NERO/2235).