Triplet states of copper and metal-free phthalocyanines

Laser flash photolysis has been used to characterise the triplet state of metal-free (H2Pc) and copper phthalocyanine (CuPc) in dilute (10–6 mol dm–3) solution in chloronaphthalene. This first observation of the triplet state of CuPc indicates that its lifetime is very short (∼35 ns), but the quantum efficiency of triplet formation ( 0.70) is greater than that for H2Pc (∼0.14). The triplet absorption maximum for both compounds occur at ≈480 nm, but the triplet energy level of CuPc (150 kJ) is higher than that for H2Pc (120 kJ).More concentrated solutions (10–4-10–5 mol dm–3) of both phthalocyanines give short-lived (100 ns) and long-lived (2.5 µs) transients, which have been attributed to the formation of excitons in microcrystalline particles dispersed in the chloronaphthalene.