Interaction between poly(vinyl pyrrolidone) PVP and fullerene C60 at the interface in PVP-C60 nanofluids-A spectroscopic study

Fourier transform infrared and Raman bands shows a discernible enhancement in band intensity of C-H stretching, C=O stretching, C-N stretching, C-H-2 bending, and C-H-2 in-plane bending in PVP molecules in the presence of C-60 molecules. Amplification in intensity is ascribed to microscopic interactions results when a donation of nonbonding electron (n) occurs from a "> N-C=O" entity of PVP into a lowest unoccupied molecular orbital of the C-60 molecule in PVP-C-60 charge transfer (CT) complex. The C=O stretching band intensity (integrated) Vs C-60 content plot exhibits a peak near a critical 13.9 mu M C-60 value owing to percolation effect. Light emission spectra show that even a small addition of 4.63 mu M C-60 able to suppress the band intensity by similar to 23% as a result of an energy loss. The integrated band intensity also decreases through a peak near 13.9 mu M when plotted against the C-60-content. In correlation to the vibration spectra, the maximum effect observed both in light emission and excitation spectra suggests a percolation effect in the CT complex. Exhibition of percolation threshold in C-60-PVP donor-acceptor complex will be helpful in optimizing the photovoltaic properties vital for solar cell applications.