During an optical pumping cycle involving electronically excited triplet states of organic molecules electron spin alignment can be transferred by the solid state effect to nuclear spin alignment. By this the sensitivity of NQR is enhanced by at least six orders of magnitude, which makes it possible to study low concentrated nuclear spin reservoirs. Applications to (1) photochemical reactions at defect site structures in molecular crystals, (2) doped organic glasses and (3) NQR on 33S in natural abundance will be discussed.