Methylene blue, absorption curve

Typical results are shown in Fig. 44. The spectral threshold of the proper photoconductivity and the photo-emf of PAC is situated at 520 nm. The spectral response for the photo emf of PAC itself is shown by curve 1. After PAC has been immersed in an ethanol solution of methylene blue and dried its spectral response is represented by curves 2 and 2. The photo-response appears in the range of the absorption maximum of the dye at 680 nm characteristic of the monomolecular form in the dilute initial solution (curve 3). The observed enhancement of the second maximum at 620 nm in comparison to the solution spectrum is obviously connected with the presence of dye dimers. The shift of the maximum photoresponse to the longer wavelength by 15 nm relatively to the solution is usually the case for the adsorbed state. The sign of the charge carriers both in the proper and sensitized spectra ranges is positive. As seen in Fig. 44 the adsorption of the dye also markedly changes the proper photosensitivity of the PAC. When the monomolecular form of the adsorbed dye dominates, the... 

Fig. 44. Spectra for the photoelectromotive force of polycopperphenylacetylenide curve (/) before, curves (22) after immersing in 1 x 10 3 ethanol solution of methylene blue curve (5) - absorption spectrum of the solution [20]...

The similarity of the absorption curves for methylene blue in stannic chloride and in sulfuric acid, given by the same authors, is a striking demonstration of the essential likeness in the behavior of these two acids toward indicators. 

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