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Photopyroelectric (PPE) spectroscopy, in the 350-1,075 nm wavelength range, was used to study the optical properties of electropolymerized melanin films on indium tin oxide (ITO) coated glass. The PPE intensity signal as a function of the wavelength lambda, V (n)(lambda) and its phase F (n)(lambda) were independently measured. Using the PPE signal intensity and the thermal and optical properties of the pyroelectric detector, we were able to calculate the optical absorption coefficient beta of melanin in the solid-state. We believe this to be the first such measurement of its kind on this material. Additionally, we found an optical gap in these melanin films at 1.70 eV.

ReceivedPhotopyroelectric spectroscopy (PPE) was used to study the thermal and optical properties of electropolymerized melanins. The photopyroelectric intensity signal and its phase were independently measured as a function of wavelength, as well as a function of chopping frequency for a given wavelength in the saturation part of the PPE spectrum. Equations for both the intensity and the phase of the PPE signal were used to fit the experimental results. From the fittings we obtained for the first time, with great accuracy, the thermal diffusivity coefficient, the thermal conductivity and the specific heat of the samples, as well as a value for the condensed phase optical gap, which we found to be 1.70 eV.

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