Laser-induced transient absorption spectroscopy of phthalocyanine dyes

Stringer, Mark Richard (1985). Laser-induced transient absorption spectroscopy of phthalocyanine dyes. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000f804

Abstract

This work reports a further investigation into the spectroscopic properties of phthalocyanine dyes in solution. The technique of nanosecond kinetic spectrophotometry was applied, with excitation at both the fundamental ruby laser output wavelength (694 nm) and the second harmonic (347 nm); corresponding in energy to the first and second excited singlet states respectively of several of the phthalocyanine compounds. The resultant transient absorption spectra indicate that the same laser—induced intermediates — those that can be identified as the lowest excited states of singlet and triplet multiplicity — are produced following excitation at either wavelength. However, the transient response also displays a marked perturbation from that characteristic of a 'simple' energy redistribution process; a perturbation that is deduced to be a consequence of both the high intensity of laser excitation and the tendency of the phthalocyanine dyes to form molecular aggregates.

Further evidence is proposed regarding the 'anomalous blue fluorescence' reported from this type of compound, with particular emphasis placed upon the need for a high degree of solute purity.