We report the spectroscopic observation of single pentacene molecules in the matrices n-tetradecane and n-hexadecane, using a confocal microscope operating at liquid-helium temperatures. A maximum detected photon emission rate of only 30 counts per second (cps) is found for pentacene in n-hexadecane and 160 cps for pentacene in n-tetradecane. For the latter system, the low count rate is shown to be caused by a high S-1 --> T-1 intersystem crossing yield of about 40% in combination with a triplet lifetime of 33 +/- 3 mu s. Pentacene molecules in this polycrystalline host are found to show little spectral diffusion on a timescale of seconds.