Photophysical and optical limiting properties of multifunctional hemi-ortho ester derivatives of fullerenol: Effects of TBAH doping, fullerenol concentration and solvent polarity

Interesting doping effect of polar impurity (tetra-butyl ammonium hydroxide, TBAH), solvent polarity and amount of fullerenol on photoluminescence and electron-transfer properties of multifunctional double bond terminated hemi-ortho ester derivatives of fullerenol is correlated on the basis of emission spectral features. Inter- and intra-molecular π–π interaction of terminal vinylic double bonds leads to cluster formation (quantitative image analysis of SEM micrographs using MATLAB tool box) and bigger cage size (on higher concentration of fullerenol) allows easy insertion of TBAH due to ionic nature and fit-in size. Antagonistic effect in fluorescence intensity in heterogeneous phase product (IB) is explained on the basis of possible TBAH intrusion inside the cage. TBAH intrusion disallows inter- and intra-molecular π–π interaction of terminal vinylic double bonds leading to high intensity (weak quenching) at higher amount of fullerenol loading (easy entry of TBAH) and strong quenching in absence of TBAH (entry difficult at low concentration of fullerenol loading). Stronger π-cation interaction is also responsible for blue shift (depopulate S1-state electron) in heterogeneous phase product (IB). Polar solvent has similar effect but lesser in magnitude due to weaker ionic character compared to TBAH. Quenching of fluorescence intensity in the presence of TBAH/polar solvent intuitively proves intra- and inter-molecular π–π electron transfer among terminal vinylic double bonds and also between π-chromophores and foreign ionic species. Preliminary results on Optical Limiting (OL) property of hemi ortho-esters are compared with fullerene and fullerenol.