The present invention is drawn to liquid perfluoro-n-alkanes that are highly transparent to UV wavelengths ranging from about 150 nm to 165 nm, and to the method by which high transparency may be obtained. The liquid perfluoro-n-alkanes of the invention are useful in optical couplants, optical cements, optical elements, optical inspection media for semiconductor wafers and devices, and immersion photolithography at 157 nm exposure wavelength.