| Abstract: | The application of polarization‐sensitive (PS) coherent anti‐Stokes Raman scattering (CARS) spectroscopy for the investigation of highly luminescent free‐base porphyrins under Qx band resonance is discussed. For coproporphyrin I tetramethyl ester (CP‐I‐TME), PS CARS spectra involving resonances with the electronic Qx absorption band as well as polarized spontaneous Raman spectra involving B band resonance are presented. A quantitative evaluation of the CP‐I‐TME spectra is performed and the results are compared to our previously presented data on free‐base octaethylporphine (OEP) and mesoporphyrin IX dimethyl ester (MP‐IX‐DME), which were obtained under identical excitation conditions. This comprehensive analysis reveals several spectral differences that can be attributed to the different β–substitution pattern of the porphyrin macrocycle. Additionally, the strong resonance enhancement of totally symmetric modes under Qx band excitation is identified as a common property for OEP, CP‐I‐TME, and MP‐IX‐DME; this enhancement selectivity distinguishes the investigated substances from what is generally observed for metallo porphyrins. Copyright © 2008 John Wiley & Sons, Ltd. |
