Phthalocyanine Fluorescence at High Concentration: Dimers or Reabsorption Effect?

Abstract

For tetrasulfonated aluminum phthalocyanine (AlPcS,), dimer formation 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 leads to anomalous observations in fluorescence spectroscopy. In the present study, we have examined the photophysical characteristics of two dye systems; AlPcS, in a 66% ethanovwater mixture and disulfonated aluminum phthalocyanine in methanol. Using absorption spectroscopy, the formation of dimers is shown to be prevalent only in the case of AIPcS,. The fluorescence emission spectra in both cases, however, exhibit similar spectral changes with increasing dye concentration. The measured fluorescence decay profiles for both dyes also show similar trends: They are monoexponential, invariant with emission wavelength and have decay times that increase with dye concentration. These distortions are sometimes incorrectly attributed to dimer fluorescence. We find no evidence for the existence of dimer fluorescence and demonstrate that these data can be readily explained, by taking into consideration the effects of reabsorption of fluorescence.

Photoinduced hole-transfer in semiconducting polymer/low-bandgap cyanine dye blends: evidence for unit charge separation quantum yield

“…To test the importance of selfabsorption in the fluorescence quenching phenomenon, we simulated PL spectra (ESIw) according to a literature model. 17 The simulated and experimental spectra agreed only for blends with very low dye concentrations (below 1 wt%), meaning that self-absorption alone is not able to explain the pronounced quenching. A decrease of PL intensity with increasing chromophore concentration has been observed in other dyes as well.…”

“…A decrease of PL intensity with increasing chromophore concentration has been observed in other dyes as well. 17,18,29 Most photophysical studies were made in solution 19,30 and often these conclusions cannot be transferred to the condensed state. In solution, one of the main non-radiative pathways for excited-state deactivation is cis-trans photo-isomerization and/or the formation of a twisted intramolecular charge transfer state.…”

“…Recently, low-bandgap cyanine dyes have been investigated for photoconductive 16 and photovoltaic applications up to 800 nm. 15 Their photophysical properties have been extensively investigated in solution [17][18][19] or when anchored to silver halide 20 or TiO 2 surfaces, 21 however, solid organic films and blends have received little attention. 22,23 In this work, we investigate the charge-transfer characteristics of four cyanine dyes in solid-state blends with poly[2-methoxy-5-(2 0 -ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and with polystyrene (PS) using absorption and fluorescence spectroscopy, and correlate these characteristics with the D-A energy levels at the heterojunction.…”

Metallo-Phthalocyanine Near-IR Fluorophores: Oligonucleotide Conjugates and Their Applications in PCR Assays

“…With very few exceptions, neither MPc dimers nor higher order cofacial aggregates fluoresce (47)(48)(49). Electronic adsorption spectra of MPc's can provide insight into groundstate aggregation processes (50); a split and blue-shifted Q-band typically indicates cofacial ground-state aggregation of Pc rings (19,44,46,51,52).…”

Fluorescent nanopigments: Quantitative assessment of their quantum yield

“…Nevertheless, we observe that, since the host-guest interactions can strongly affect the dye fluorescence efficiency, measuring the quantum yield of both organic-inorganic and organic-organic fluorescent nanoparticules is of paramount importance for the development of any optophotonic application. Unfortu-nately, although the optical properties and the fluorescence efficiency of most organic dyes are reported in the literature 45 and/or can be easily measured in solution, 46,47 very few systematic and quantitative studies on the quantum yield of fluorescent nanopigments can be found in the literature 18,19 and a precise measurement is often lacking. On one hand, the relative quantum yield is indeed commonly estimated by comparison with a well-know fluorescent agent in solution taken as reference.…”