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Absorption and fluorescence spectra are central to the photosciences. The PhotochemCAD initiative, aimed at assembling digital databases of absorption and fluorescence spectra for use across the photosciences, now comprises <1000 absorption spectra and <500 fluorescence spectra for ~1000 compounds along with companion photophysical parameters (molar absorption coefficient, fluorescence quantum yield) and citations to the originating scientific literature. The spectral databases have chiefly been assembled by digitizing spectra from the vast print literature. The conversion of print spectra to digital form presents several technical challenges: (1) print spectra are plagued by line crossing from overlaid spectra, use of discontinuous lines, and interference from grids, tick marks, and the graph baseline; (2) the print spectrum in some cases lacks wavelength markers or is annotated with markers at odds with values in the accompanying text; and (3) the digitized spectra often are composed of data with uneven wavelength (x-axis) intervals. Here, manually assisted digitization – wherein the user steps through a print spectrum with hand-eye assistance to create the corresponding digital dataset – is compared with automated digitization. Graphical features that bear on use of each method are outlined. Two spreadsheet-based tools have been developed for application following digitization: (i) conversion of xy-coordinate data from uneven to uniform x-axis intervals, and (ii) calibration of the digitized spectrum with appropriate wavelength values. The two tools enable more accurate rendition of print spectra into digital form, as required for qualitative comparisons and quantitative calculations, and have been added to the PhotochemCAD website (http://www.photochemcad.com).
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