Spectroscopic properties of non-amphiphilic 1-pyrene carboxaldehyde assembled in Langmuir-Blodgett films

l-Pyrene carboxaldehyde (abbreviated as PyCHO), a non-amphiphilic derivativ e of pyrene has been successfully incorporated in Langmuir-Blodgett (LB) fi lms, mixed with stearic acid (SA). Surface pressure ( rr) vs. area per mole cule isotherms of PBCHO mixed with SA at different mole fractions reveal a plateau like region which indicates a phase transition corresponding to a r eorientation of the PyCHO molecules at the air-water interface. Moreover, a positive deviation from the ideal behaviour of the area per molecule in di fferent mole fraction in the mixed film at the air-water interface clearly reveals a repulsive interaction between the components resulting in the for mation of aggregates of PyCHO molecules in the mixed films. Unlike pyrene m olecules, formation of J-aggregates of PyCHO molecules in the mixed LB film s has been confirmed by absorption spectroscopic studies. The fluorescence spectrum of the LB mixed film of PyCHO has been observed to lie between the solution and microcrystalline spectra and has a combination of both monome ric and excimeric species. A striking similarity between the LB film emissi on spectra and the emission spectra of PyCHO in ethanol-water binary mixtur e confirms the formation of low dimensional microcrystalline aggregates in the LB film. (C) 2000 Elsevier Science Ltd. All rights reserved.