Axial halogen ligand effect on photophysics and optical power limiting of some indium naphthalocyanines.

Three axially substituted complexes, 2,3-octa(3,5-di-tert-butylphenoxy)-2,3-naphthalocyaninato indium chloride (1a), 2,3-octa(3,5-di-tert-butylphenoxy)-2,3-naphthalocyaninato indium bromide (1b), and 2,3-octa(3,5-di-tert-butylphenoxy)-2,3-naphthalocyaninato indium iodide (1c) have been synthesized and their photophysical properties have been investigated. Optical power limiting of nanosecond (ns) and picosecond (ps) laser pulses at 532 nm using these complexes has been demonstrated. All complexes display strong Q(0,0) absorption and measurable emission in the near-infrared region and exhibit strong excited-state absorption in the range of 470-700 nm upon ns laser excitation. The different axial ligands show negligible effect on the linear absorption, emission, and transient difference absorption spectra. However, the excited-state lifetime, triplet excited-state quantum yield, and efficiency to generate singlet oxygen are affected significantly by the heavier axial ligand. Brominated and iodinated complexes 1b and 1c show higher triplet excited-state quantum yield, while chlorinated complex 1a has longer excited-state lifetime and is more efficient in generating singlet oxygen. The iodinated complex 1c displayed the best optical limiting due to the higher ratio of excited-state absorption cross section to ground state absorption cross section (sigma(eff)/sigma(0)).