Stiffness tunable molecular spring washers: high-pressure Raman investigations on porphyrin self-assemblies

The Raman spectra of a series of meso-substituted porphyrin self-assemblies have been measured as a function of pressure up to 13 GPa. In comparison with that for Tpp J-aggregates in our previous investigation [J. Phys. Chem. B, 2008, 112, 15562], a similar phenomenon has been observed in all meso-substituted self-assemblies, such as peaks in the spectrum which show positive linear pressure dependence which provides no evidence of the phase transition and the intensity enhancement of aromatic Psi(3) C-C stretching vibration with pressure. The different slopes of intensity ratios between Psi(3) C-C and C(a)-C(m) stretching vibration to pressure in these meso-substituted porphyrin self-assemblies indicate that the stiffness of molecular spring washers is tunable.