Interlayer Energy Transfer between Carbazole and Two 9-Anthroyloxy Derivatives in Langmuir−Blodgett Films

The interlayer excitation energy transfer between 11-(9-carbazole)undecanoic acid (11-CU) and two 9-anthroyloxy derivatives, 9-(9-anthroyloxy)stearic acid (9-AS) and 2-(9-anthroyloxy)stearic acid (2-AS), in alternating multilayer Langmuir−Blodgett films has been studied. The 11-CU fluorescence is quenched by energy transfer to 9-AS or 2-AS as judged by steady-state and picosecond time-resolved fluorescence measurements. The fluorescence decay curves of 11-CU in the films were analyzed in the framework of several models: (1) a general model for interlayer energy transfer, (2) a two-exponential decay, (3) a Förster model for energy transfer in a two-dimensional system, and (4) a stretched-exponential decay, characteristic of Förster energy transfer in self-similar fractal-like structures. The recovered decay parameters suggest an inhomogeneous mixing of the acceptor molecules in LB films leading to a two-phase system. The phase separation during compression of the acceptor monolayers forms regions of acceptor concentration about 3 times that of the intended and regions with very low acceptor concentration.