When a polymer material with molecular vibration absorption is used for the dielectric (insulator) layer in the MIMthe structure named molecular assembled metasurfaces -the weak and strong coupling phenomena are observed between the metasurface resonance and the molecular vibration absorption mode . In the case of weak-coupling, spectral distortion and surface-enhanced IR absorption (SEIRA) due to the Fano resonance are observed. The strong-coupling can be also observed when plasmon resonance and molecular vibrational absorption band are strongly overlapped (in wavelength). We found that a narrow-band light source can be realized from the radiation spectrum of a molecular assembled metasurfaces with a conventional broadband absorption property, when there is a match of structure and molecular resonances . This indicates that it is possible to realize a very useful narrow-band light source for analytical systems at the IR absorption window, where such sources and spectral filters are not (or less) available.