Is there a chemical(s) that provides good discrimination between absorbance curves for different pHs in the UV light spectrum (100-400nm?)
There are some good examples in Multiwavelength Spectrophotometric Determination of Acid Dissociation Constants Pharaceutical Research Volume 16, Issue 3, pp 374-381.
Benzonic acid (pka = 3.98), phenol (pka 9.73), phthalic acid (pkas 2.70 and 4.86), nicotinic acid (pKas 2.1 and 4.63) and p-aminosalicylic acid (pKas 1.79 and 3.58) would be good in the ~220nm-300nm range.
Red cabbage indicator absorbs the uv and visible radiations from520nm to600 nm range.For every pH the colours as well as the absorptions are also different. It shows deep red in pH 1,light red in 2,pink in 3,light pink in 4,5,6,purple in7,light purple in 8,light violet in 9,violet in 10,blue in 11,green in 12,yellow in 13 and deep yellow in 14.