1 research outputs found
Enhancing Organic Semiconductor–Surface Plasmon Polariton Coupling with Molecular Orientation
Due to strong electric
field enhancements, surface plasmon polaritons
(SPPs) are capable of drastically increasing light-molecule coupling
in organic optoelectronic devices. The electric field enhancement,
however, is anisotropic, offering maximal functional benefits if molecules
are oriented perpendicular to the interface. To provide a clear demonstration
of this orientation dependence, we study SPP dispersion and SPP-mediated
photoluminescence at a model Au/small-molecule interface where identical
molecules can be deposited with two very different molecular backbone
orientations depending on processing conditions. First, we demonstrate
that thin films of <i>p</i>-SIDTÂ(FBTTh<sub>2</sub>)<sub>2</sub> can be deposited with either all “in-plane”
(parallel to substrate) or a 50/50 mix of in-plane/“out-of-plane”
(perpendicular to substrate) optical transition dipoles by the absence
or presence, respectively, of diiodooctane during spin-coating. In
contrast to typical orientation control observed in organic thin films,
for this particular molecule, this corresponds to films with conjugated
backbones purely in-plane, or with a 50/50 mix of in-plane/out-of-plane
backbones. Then, using momentum-resolved reflectometry and momentum-resolved
photoluminescence, we study and quantify changes in SPP dispersion
and photoluminescence intensity arising solely from changes in molecular
orientation. We demonstrate increased SPP momentum and a 2-fold enhancement
in photoluminescence for systems with out-of-plane oriented transition
dipoles. These results agree well with theory and have direct implications
for the design and analysis of organic optoelectronic devices