Papanikolas Group
Ultrafast Spectroscopy and Ultrafast Microscopy
Papanikolas Group
Ultrafast Spectroscopy and Ultrafast Microscopy
Group Members
Light-Harvesting Assemblies
The characterization of charge and energy transport in large multicomponent assemblies is a challenging problem. Transport depends upon the macromolecular structure, which in turn depends upon the scaffold and the chemical structure of the monomer. The separation between adjacent components is described not by a single distance but rather by a distribution of distances that results in a distribution of electron and energy transfer rates. We use transient absorption and emission spectroscopies to characterize the excited state dynamics in assemblies consisting of 20-70 chromophores. Large-scale computer simulations provide insight into fundamental dynamics of transport. These project involve partnerships with groups that are experts in the synthesis of molecular assemblies based on polymer (Meyer, Schanze, Reynolds) and peptide (Waters) scaffolds .
Thomas Meyer
Marcey Waters
John Reynolds
Kirk Schanze
Research Highlights
Solar fuels generation requires molecular assemblies that can perform multiple functions. In collaboration with the Schanze and Reynolds groups, we have examined the excited state dynamics of a functionalized polyfluorene polymer anchored to TiO2. The evolution of the transient spectra are followed across 8 decades of time, revealing that photexcitation of the Ru(II) complexes is followed by site-to-site energy transport, electron injection, and ultimately the transfer of the oxidative equivalent to the polymer backbone. The resulting charge separated state lives for about 100 usec. <Read>
A Raman-pump frequency modulation scheme and an automated signal-processing algorithm were developed for improved collection of time-resolved FSRS spectra. Together, these two advancements remove the broad background signals endemic to FSRS measurements and retrieve signals with high sensitivity. This FM-FSRS method was applied to the characterization of ultrafast energy transport in a OPE-TBT copolymer. Ultrafast energy transfer is monitored by the decay of donor vibrational modes and simultaneous growth of acceptor modes. <Read>
Observation of Combined Light-harvesting and Charge Separation in a Functionalized Assembly Bound to TiO2
In the beginning...
Ru(II)-Loaded Polystyrene
Early work in our lab examined assemblies consisting of 20 Ru(II) complexes linked together by a polystyrene scaffold. Using ultrafast absorption and emission methods we examined energy transport, triplet-triplet annihilation.
Energy Transfer in Folded Peptide Dimers
In collaboration with the Waters group, we have examined energy transfer in a coiled-coiled peptide dimer functionalized with a Ru(II) donor and and Os(II) acceptor. <Read>
Recent Review
Observation of excited state trapping in rigid environments. Implies side chain motion matters. <Read>
Experimental observation and modeling of site-to-site energy transport by Monte Carlo and stochastic kinetic simulations. <Read>
Characterized triplet-triplet annihilation process involving the interaction of multiple excited states on a single chain. <Read>
Ultrafast Dynamics
in Assemblies with Conjugated Backbones
Two recent publications appearing in J. Phys. Chem. Lett. explore competitive energy and electron transfer processes following photoexcitation of the polymer scaffold in macromolecular assemblies based on conjugated polymers (i.e. polyfluorene and P3HT).
Polyflourene:
Competitive energy and charge separation
P3HT:
Formation of long-lived charge separated state
P3HT-Ru
Frequency-Modulated FSRS Spectroscopy Applied to Energy Transport in a Light-Harvesting Polymer
Papanikolas Group
Department of Chemistry
University of North Carolina at Chapel Hill