Excitonic dynamics of Chlorophyll-a molecules in chitosan hydrogel scaffold.

Biomimetic photo harvesting architecture has been proposed as an alternative for existing solar conversion systems. This fact led us to the successful realization of non-coherent electron hopping [hopping rate 4.28 ns(-1)] through excitonically coupled Chlorophyll-a (Chl-a) molecules within chitosan hydrogel matrix via TCSPC (Time Correlated Single Photon Count) and fluorescence anisotropy measurements. Chl-a molecules remain stable within the hydrogel matrix up to 3 months, as evidenced from UV-vis spectroscopy. The mono-exponential decay parameter with 78 picoseconds time scale, high initial anisotropy data [r0 = 0.33] and with reduced TCSPC lifetime [1.311 ns] of 23° in plane aligned Chl-a macrocycles, indicate that hopping excitonic cascade is prominent among chlorophyll molecules. From the Raman Spectra, it can be postulated that they form a highly co-ordinated closely packed structure via water molecules within chitosan hydrogel due to 6th co-ordination through central Mg of porphyrin macrocycle. All these data predict that this chlorophyll-chitosan hydrogel can be an active component in artificial light harvesting systems.