This paper reports on fluorescence microscopy and spectroscopy of single te
rrylene molecules embedded in p-terphenyl at room temperature. The basic ph
otophysical parameters of this crystalline host/guest system such as photos
tability, single-molecule emission rates and the properties of dispersed fl
uorescence spectra are reported. The stability of the single-molecule signa
ls allowed the direct observation of singlet-triplet quantum jumps at room
temperature, by means of which the underlying intersystem crossing rates ca
n be investigated. The results of earlier investigations at Liquid-helium t
emperatures an reviewed briefly where appropriate. The properties of terryl
ene in p-terphenyl are also compared to those of other host/guest systems a
t room temperature. (C) 1999 Elsevier Science B.V. All rights reserved.