A new way of preparing thin films of phthalocyanines (PC) is demonstrated. Starting from the precursor isoindoline 2, a solid-state synthesis of Mn and Zn PC 3a and 3b in thin films by a thermoreaction is described. The optical properties of the thin films which absorb strongly in the near infrared are investigated. Parameters such as film thickness, optical spectra, film composition and PC 3 yield are measured and calculated using optical and mechanical methods. The data also indicate that the conversion of isoindoline 2 into PC 3 is very efficient.