PHTHALOCYANINE FLUORESCENCE AT HIGH-CONCENTRATION - DIMERS OR REABSORPTION EFFECT

Citation
S. Dhami et al., PHTHALOCYANINE FLUORESCENCE AT HIGH-CONCENTRATION - DIMERS OR REABSORPTION EFFECT, Photochemistry and photobiology, 61(4), 1995, pp. 341-346
Citations number
27
Categorie Soggetti
Biophysics,Biology
ISSN journal
00318655
Volume
61
Issue
4
Year of publication
1995
Pages
341 - 346
Database
ISI
SICI code
0031-8655(1995)61:4<341:PFAH-D>2.0.ZU;2-8
Abstract
For tetrasulfonated aluminum phthalocyanine (AlPcS(4)), dimer formatio n is characterized in the absorption spectrum by a broadening of the Q -band and the appearance of a new band at the red edge of the spectrum . The high concentrations required to produce dimers, however, often l eads to anomalous observations in fluorescence spectroscopy. In the pr esent study, we have examined the photophysical characteristics of two dye systems; AlPcS(4) in a 66% ethanol/water mixture and disulfonated aluminum phthalocyanine in methanol. Using absorption spectroscopy, t he formation of dimers is shown to be prevalent only in the case of Al PcS(4). The fluorescence emission spectra in both cases, however, exhi bit similar spectral changes with increasing dye concentration. The me asured fluorescence decay profiles for both dyes also show similar tre nds: They are monoexponential, invariant with emission wavelength and have decay times that increase with dye concentration. These distortio ns are sometimes incorrectly attributed to dimer fluorescence. We find no evidence for the existence of dimer fluorescence and demonstrate t hat these data can be readily explained, by taking into consideration the effects of reabsorption of fluorescence.