We consider the collection efficiency for photons emitted by a single
molecule in a solid excited by monochromatic light at low temperature,
which depends upon the dipole radiation pattern; the orientation of t
he emission dipole, total internal reflection, and the numerical apert
ure of the collecting optics. By using the complete expression for the
collection efficiency and varying the collection angle, we have deter
mined the orientation of the dipole of a single terrylene molecule in
hexadecane to be almost perpendicular to the substrate. By using satur
ation data we find that the angle between the optical axis of the coll
ection paraboloid and the emission dipole moment is 16 +/- 6 degrees.
We estimate that the true saturation intensity of terrylene (for dipol
e moment parallel to the electric field of the light) is about (80+/-3
0) mW/cm(2) and that the ratio of the intersystem crossing rate to the
total decay rate of the triplet state is about 3.3 +/- 1.2.