Intramolecular π-π Interactions in Platinum(II) Metalloporphyrin Dimer Homologues with Aliphatic Chains of Different Lengths

The synthesis and thermal stabilities, spectroscopic and electrochemical properties for a series of platinum(II) metalloporphyrin dimer complexes with aliphatic chain of different lengths [-O(CH2)(n)O-] have been studied. Although dimeric porphyrin ligands and platinum(II) complexes display nearly the same absorption spectra in the concentration range from 10(-7) to 10(-4) mol.dm(-3), these ligands and their complexes show concentration-dependent emission when the length of aliphatic chain is beyond four carbon atoms. At elevated concentration of the ligands and complexes, the emission spectra show obvious red-shifts. For complex Pt2C6(OPTPP)(2) and Pt2C10 (OPTPP)(2), the emission maxima at 652 nm are red-shifted to 676 and 681 nm at concentrations >10(-4) mol.dm(-3). Emission spectra of the sublimate films of complexes also display similar red-shifts: 43 nm for Pt2C6(OPTPP)(2) and 53 nm for Pt2C10(OPTPP)(2). The concentration-dependent emission indicates that there are intramolecular pi-pi interactions in porphyrin dimers and platinum(II) metalloporphyrins.