Optical and structural properties of chlorophyll a aggregates in PVA film

Abstract

The aggregated properties of Chlorophyll a (Chla) in polymer play a pivotal role in light capture and transfer as photostable pigment sensitizers of solar power systems. Here, we embedded the natural Chla molecules (2 × 10−3 M) extracted from spinach leaves into polyvinyl alcohol (PVA) films by casting method under different temperature. UV–VIS, fluorescence, Circular Dichroism (CD) spectroscopy, and Transmission Electron Microscopy (SEM) have been applied to investigate the optical properties and aggregated structures in detail. The excited state dynamics of these aggregates in PVA were explored using Time-Correlated Single Photon Counting (TCSPC). The de-composited components from absorption, emission, TCSPC and the CD shapes in the study show the analogous characteristics to the photosystem of cyanobacteria in some papers that features a coexisting of several aggregates (dimer, oligomer, bulk oligomer), in which the proportion of bulk oligomer can be greatly promoted under lower temperature (0 °C) due to the involvement of a large amount of water. The analysis of spectral and dynamical components reveals the bulk oligomer model of Chla in PVA, which is constructed from several oligomers by PVA chain and water. Besides, a specific red trapping center within bulk oligomer is proposed to perform capturing energy in 18 ps, which is located on the lowest end of energy flow and devotes large than 99% florescence in TCSPC.