Thermal behavior of mixed-stack charge transfer (CT) films prepared by 5,10-dimethyl-5,10-dihydrophenazine ((Me)(2)P) doping of Langmuir-Blodgett (LB) films of 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (octadecyl-TCNQ) has been investigated by using X-ray diffraction and ultraviolet-visible-near-infrared (UV-vis-NIR) and infrared (IR) spectroscopies. Temperature-dependent changes in the UV-vis-NIR and IR spectra reveal that donors (D, (Me)(2)P) dedope from the CT complex, resulting in a restoration of accepters (A, octadecyl-TCNQ) to their neutral state in the temperature range 70-90 degrees C. The dedope temperature was determined to be 80, 84, 86, and 88 degrees C for the 1-, 3-, 7-, and 11-layer CT films, respectively, by monitoring an a, C=N stretching band of the TCNQ chromophore in the temperature-dependent IR spectra. From room temperature to 60 degrees C, the molecular arrangement and orientation of D and A in the well-ordered multilayered CT complex seem to be thermally stable because the X-ray diffraction pattern and UV-vis-NIR and IR spectra are nearly unchanged. The dedoping begins in the temperature range 60-70 degrees C, but it proceeds rather slowly for the multilayered CT films. Dramatic structural changes take place in the region of 70-90 degrees C, where the X-ray diffraction pattern and characteristic absorption bands of the CT complex in the UV-vis-NIR and IR spectra disappear. The thickness-dependent thermal behavior may be attributed to the longitudinal interactions between the sheetlike multilayered microcrystals as well as to the interaction between the first layer and a CaF2 substrate.