Antenna Doping: The Key for Achieving Efficient Optical Wavelength Conversion in Crystalline Chromophoric Heterolayers

Abstract : High-yield wavelength conversion is one of the key requirements for efficient photon energy harvesting. Attempts to realize efficient conversion by simply stacking layers of chromophores have failed so far, even when using highly crystalline assemblies and employing the recently discovered long-range (>100 nm) Förster resonance energy transfer, LR-FRET. We were able to drastically improve optical conversion efficiency by using chromophoric metal-organic framework (MOF) heterolayers fabricated using layer-by-layer techniques in connection with an "antenna doping" strategy. Systematic investigations revealed that the LR-FRET mechanism, reported previously in chromophoric aggregates, is highly anisotropic for neat materials but can be made more isotropic by employing doping strategies. Using optimized fabrication parameters and dopant concentrations, a three-layer, two-step cascade with an overall optical conversion efficiency of ~ 75% has been realized.