The photochemical interaction between halogenoheterocyclic derivatives and aromatic and/or heteroaromatic compounds is discussed. Special attention was given to furan, thiophene, and pyrrole derivatives. The reaction with arenes shows a wide applicability of photochemical arylation with furan and thiophene derivatives. On the contrary, halogenopyrrole derivatives do not give arylation reaction usefully. Kinetic and spectroscopic data are in agreement with the formation of a transient triplet exciplex in this type of reaction. Some applications of the synthesis of naturally occurring polythiophenes are reported. The target compounds are obtained through photoarylation and subsequent reaction with alkynes in the presence of palladium (0) complexes as catalysts. The reaction of halogenoheterocyclic derivatives with arylakenes gives the substitution product on the alkene. In the presence of electron-withdrawing substituents on the alkene the observed reaction is the photoarylation. In the presence of arylalkynes a mixture of products is obtained, but photochemical substitution on alkyne can be selectively obtained  using protected arylalkynes. The photochemical properties of some synthesized compounds are tested in order to establish whether they are singlet oxygen sensitizers. All the compounds tested are singlet oxygen sensitizers. Photobiological tests are carried out on some indenylthienyl derivatives showing that direct relationship between photooxidation properties and phototoxicity is not necessarily correct.