A systematic study of the efficiency of photoluminescence (PL) quenching of nanocrystalline porous Si by aromatic triplet energy accepters was carried out. The effects of molecular triplet energy, molecular size, and the porous Si emission energy on PL quenching efficiency were probed. Photoluminescent porous Si samples, prepared by electrochemical etch, were titrated with toluene solutions of anthracene, 9,10-diphenylanthracene, 9,10-dichloroanthracene, 9,10-dimethylanthracene, pyrene, 1,2-benzanthracene, acridine, and 1,4-diphenyl-1,3-butadiene, and the steady-state and time-resolved PL spectra were measured. The quenching of PL adequately fits a dynamic Stern-Volmer quenching model. The rate of quenching increases with increasing exoergicity, and then levels off at higher exoergicities. The mechanism of quenching is attributed to energy transfer from the porous Si excited state to the triplet levels of the quencher molecules. The rate of quenching can also be affected by the size of substituents on the quenchers; some molecules with larger substituents display slower quenching rates than expected from their triplet energies.