We have measured the fluorescence decays of pentacene (Pe) dispersed in Shpol'skii matrices of n-heptane, n-tetradecane and n-hexadecane in the temperature range 1.7-200 K. In all of these matrices the decay times were about 25 ns at 1.7 K and shortened to less than 15 ns at high temperatures. This result suggests a low value of the intersystem crossing (ISC), S-1 --> T-1, yield at 1.7 K. To check this hypothesis we studied the fluorescence intensity auto-correlation decays of single Pc molecules in n-tetradecane at 1.7 K. The analysis led to a value of the triplet population yield of about 1.5%.