Single molecule Raman spectra of porphycene isotopologues

Abstract

Single molecule surface-enhanced resonance Raman scattering (SERRS) spectra have been obtained for the parent porphycene (Pc-d₀) and its deuterated isotopologue (Pc-d₁₂), located on gold and silver nanoparticles. Equal populations of “hot spots” by the two isotopologues are observed for 1 : 1 mixtures in a higher concentration range of the single molecule regime (5 × 10⁻⁹ M). For decreasing concentrations, hot spots are preferentially populated by undeuterated molecules. This is interpreted as an indication of a lower surface diffusion coefficient of Pc-d₁₂. The photostability of single Pc molecules placed on nanoparticles is strongly increased in comparison with polymer environments. Trans tautomeric species dominate the spectra, but the analysis of time traces reveals transient intermediates, possibly due to rare cis tautomeric forms.