Effect of peripheral substitution on the optical limiting properties of zinc phthalocyanines

Abstract

Six zinc phthalocyanines with peripheral propanethio or p-methylbenzenethio groups, namely 1,8,15,22-tetrapropanethiophthalocyaninatozinc(II) (1), 1,8,15,22-tetra(p-methylbenzenethio)phthalocyaninatozinc(II) (2), 2,9,16,23-tetrapropanethiophthalocyaninatozinc(II) (3), 2,9,16,23-tetra(p-methylbenzenethio)phthalocyaninatozinc(II) (4), 2,3,9,10,16,17,23,24-octapropanethio phthalocyaninatozinc(II) (5), 2,3,9,10,16,17,23,24-octa(p-methylbenzenethio) phthalocyaninatozinc(II) (6) were synthesized for optical limiting study at 532 nm (pulse duration: 5 ns, repetition rate: 20 Hz). All of the compounds exhibited good optical limiting property when measured in dichloromethane solution in a quartz cell (pathlength: 1 mm, linear transmission: 75 %). The limiting thresholds (Fth, T/T0 = 0.5) of these metal phthalocyanines were found to be 0.91, 1.1, 0.38, 0.5, 0.18, 0.15 J cm-2 from complexes 1 to 6, respectively. The difference in their optical limiting performance can be attributed to their different ratio between excited state and ground state absorption cross section (σex/σg), as demonstrated by Z scan measurements. C60 and (t-Bu)4PcInCl, benchmark optical limiting materials at 532 nm, were measured under the same conditions for comparison.