On the possibility of observation of single quadrupoles by fluorescence resonance energy transfer scanning near-field optical microscopy

The possibility to observe single quadrupoles by the recently proposed fluo rescence resonance energy transfer scanning near-field optical microscopy ( FRET SNOM) is analyzed. When an excited dipole donor center of the SNOM tip is scanned close to a quadrupole molecule of the sample (at a distance of 1-2 nm), the probability of donor-quadrupole FRET becomes close to unity. T hus a single quadrupole can be imaged as a donor fluorescence quenching or by observing dielectric tip-enhanced fluorescence of the quadrupole. To the best of our knowledge, this is the only existing possibility to visualize single quadrupoles. (C) 2001 Published by Elsevier Science B.V.