Studies On Spectra Characteristic Of Organic Cyanine Dye Langmuir-Blodgett Film

The elementary knowledge of the Langmuir-Blodgett(LB) film has been introduced in brief.We prepared several cyanine dye LB films,and made a thorough investigation on its optical characteristic.Firstly,the optical properties of cyanine dye(HQ) in Langmuir-Blodgett films were studied over the UV-visible range by means of spectroscopic ellipsometer(SE). The high absorption of the LB films at different frequencies was analyzed.Theoretical computation and numerical fitting with Lorentz oscillator model was also carried out. It is found that the fitted results are in good agreement with the experimental data.Secondly,we researched the aggregation status,the molecular structure,and the molecular orientation by UV-visible absorption measurements.The "blue-shift" was found in the UV-visible spectrum of the HQ LB films.It's suggested that the HQ LB films have the H-aggregation.From the relationship between absorbency and the absorption coefficient of monolayer,we can know that the absorption coefficientμof monolayer in HQ LB films is correlative to the wavelength of incidence light,that isμ(λ)=lg(I₀/I)*ln(10/x).The orientation angle of the macro ring was calculated, and it's well coincident with the result deduced from the surface pressure-area isotherm.Finally,we report our measurement result by using Fluorescence spectrum.By comparison with spectrum of cyanine solution,LB film showed clear blue shift.This result is consistent with our measurement before,and gives a decisive proof of the existence of H-congregation in LB film.Meanwhile,the measurement of fluorescence decay profiles could be used to quantitatively characterize the lifetime,weight and size of aggregates.