SEF of Langmuir-Blodgett Films

In 1988, the distance dependence of surface-enhanced fluorescence was studied for Langmuir-Blodgett monolayers deposited on silver island films. This study was inspired in part by two earlier reports that examined the distance dependence of SERS of LB films on metal surfaces. Varying numbers of spacer layers of arachidic acid were employed in order to probe the competition between EM enhancement and radiationless energy transfer for a phthalocyanine monolayer. In direct contact with the metal surface, a broadened, enhanced, and red-shifted fluorescence spectrum was observed. These spectral changes can be attributed to a drastic decrease in the fluorescence lifetime of the molecule when it is placed in contact with the metal surface. However, an enhanced version of the unperturbed spectrum was observed when intervening spacer layers were introduced. It was found at enhancements on the order of about 400 could be realized when S monolayers were placed between the Ag island film and the phthalocyanine monolayer. 

For some time now, we have been working with many different perylene derivatives in the study of surface-enhanced spectroscopies such as SERS, SERRS, SEF, and SEIRA (surface-enhanced infiared absorption). These molecules show a very strong tendency towards aggregation at high concentrations, and often display excimer fluorescence in concentrated Langmuir-Blodgett monolayers. The surface-enhanced 

A large portion of the work that has been done in our group on the surface-enhancement of fluorescence from LB monolayers has been in conjunction with surface-enhanced Raman studies. In theses studies, SEF has been helpful in providing information about the aggregation, and orientation of dye molecules, as well as information about the thermal stability of the monolayers used. A separate study reported the effects of different variables pertaining to the fabrication of LB films. In particular. 

SEF was used to probe monolayers prepared at different surface pressures (varying the degree of condensation of the monolayer), and on subphases of different pH values. 

Before concluding this section on the surface-enhanced fluorescence of Langmuir-Blodgett films, two papers that show the expansion of this technique beyond classic dye systems will be discussed. The first of these papers, by Sokolov, Chumanov, and Cotton, was published in 1998 and employed colloidal metal silver films (CMFs) coated on functionalized glass substrates towards the improvement of bioanalytical 

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