The optical limiting (OL) properties of free-base phthalocyanines and nickel metallophthalocyanines with the same structure but, with different substituent groups, octa-dodecaoxyl long chains, were investigated by using nanosecond pulses at 532 nm. The experimental results show that the OL capabilities in the two kinds of phthalocyanines depend nonmonotonically on lengths of the side chains. (C) 2002 Elsevier Science B.V. All rights reserved.