Photophysical and photochemical measurements have been made on a series of novel alpha octa(alkyl-substituted) silicon, zinc and palladium phthalocyanines for which the synthesis is outlined. Fluorescence quantum yields and lifetimes, triplet quantum yields and lifetimes and singlet delta oxygen quantum yields were measured in 1% v/v pyridine in toluene. The effects of varying central atom and addition of alkyl substituents relative to unsubstituted parent molecules, zinc phthalocyanine (ZnPc) and silicon phthalocyanine (SiPc), are discussed. All phthalocyanines studied exhibit absorption and emission maxima in the region of 680–750 nm with molar absorptivity of the Q-band ∼105 M−1 cm−1. The series of compounds also exhibited triplet quantum yields of 0.65–0.95 and singlet oxygen quantum yields of 0.49–0.93.

Photophysical and photochemical measurements have been made on a series of novel non-peripherally octa(alkyl-substituted) zinc phthalocyanines. Fluorescence quantum yields and lifetimes, triplet quantum yields and lifetimes and singlet delta oxygen quantum yields were measured in 1% v/v pyridine in toluene. The effects of alkyl substituents and increasing chain length relative to the unsubstituted parent molecule, zinc phthalocyanine (ZnPc), are discussed. ZnPc with alkyl substituents of chain length 5–15 carbons exhibited similar absorption and emission maxima (704 nm and 718 nm respectively) with the molar absorptivity of the Q-band ∼105 M−1 cm−1. The series of compounds also exhibited triplet quantum yields of 0.78–0.84 and singlet oxygen quantum yields of 0.67–0.71.

The absolute absorption cross-section of OIO was measured from 558 to 578 nm by using cavity ring-down spectroscopy to measure the fraction of OIO removed following absorption of a laser pulse of known fluence. This procedure yields σOIO = (1.51 ± 0.18) × 10−17 cm2 at 567.93 nm, which is one of the prominent vibrational band peaks in the OIO spectrum. The recovery of ground-state OIO after a few microseconds indicates that, after excitation from the ground 2B1 to the (first) excited 2B2 state, OIO undergoes rapid internal conversion onto high vibrational levels of the 2B1 state, followed by quenching collisions with the bath gas. A detailed kinetic model is used to show that the OIO yield from the IO self reaction is 0.31 ± 0.10 at 40 Torr and 293 K. The rapid removal of OIO in the reactor is explained by the recombination of atomic I and OIO with a rate constant of (1.1 ± 0.3) × 10−10 cm3 molecule−1 s−1. Ab initio calculations combined with RRKM theory are used to show that this rate constant is consistent with the addition of the I atom to the central I, rather than either of the terminal O atoms. The unexpectedly fast disappearance of I atoms, and the corresponding formation of I2, is explained by iodine oxides such as IO, OIO and I2O3 acting as chaperone molecules.