Photochemistry of Merocyanine 540

Abstract

The photophysical properties of merocyanine 540 have been determined in methanol solution over a modest temperature range. Triplet state population is inefficient (the limiting triplet quantum yield being 0.25) due to rapid isomerization of the central double bond from the first excited singlet state. Activation energies have been measured for isomerization from the excited singlet state (20 kJ mol-1) and for conversion of the resultant cis-isomer back to the original trans-form (63 kJ mol-1), both processes involving formation of a twisted species. The dye is easily oxidized to give an unstable adduct which decomposes on the sub-ms timescale. Reversible redox chemistry occurs upon excitation in the presence of electron acceptors. These various observations are discussed in terms of the known chemotherapeutic activity of MC540 and it is concluded that the most probable mechanisms for cytotoxicity involve either local thermal disruption of cell membranes or in situ photogeneration of toxins derived from breakdown of the dye.

Effect of Sodium Chloride on Aggregation of Merocyanine 540 and Photosensitized Inactivation of Staphylococcus aureus and Pseudomonas aeruginosa

“…It is known that the aggregation state of MC540 defines the type of photodynamic reactions that occur and affects the formation of active products, which can inflict damage on biological molecules [13] and can also influence the rate of MC540 photobleaching [7, 8]. The production of singlet oxygen ( 1 O 2 ) was believed to play the main role in the bactericidal activity of photosensitizers [5, 14].…”

“…It may be suggested that the transfer of an electron between the excited and unexcited molecules of the dye is facilitated in the aggregates of MC540. In all likelihood, the presence of the salt causes the activation of photodynamic reactions in the aggregates of MC540, which results in the generation of free radicals [13], the latter having the ability to attack bacteria and, subsequently, to kill them. …”

Photo‐isomerization of the Cyanine Dye Alexa‐Fluor 647 (AF‐647) in the Context of dSTORM Super‐Resolution Microscopy

“…The characteristics inusoidal pattern ( Figure S46) corresponding to ground-state bleach and transienta bsorption at slightly longerw avelengths implies formation of ap hoto-isomer (Figure 7). [84] Reconstruction of the isomer absorption spectrum was achievedb yadding successive amountso fg round-statea bsorption to the transient signal until the ground-state bleach had been completely re-covered.T his approach indicates that the absorption spectrum of the isomer is red-shifted by 37 nm compared to the ground-state. Multi-variate spectral curve fitting [85] leads to an estimate fort he molar absorption coefficient at the peak maximum of 230,000 m À1 cm À1 .G lobal analysis indicates that the lifetimeo ft he isomer is around6 00 msi na ir-equilibrated solution at room temperature.…”

Spin–orbital coupling effects on the photophysical properties and photocytotoxicity of merocyanine dyes

“…According to the simple potential-energy diagram given as Fig. 6, the total activation energy for internal conversion can be estimated from 5) where is the potential energy at the top of the barrier, E B assuming this latter term remains constant for all members of the series. The validity of this latter assumption is conÐrmed by the realization that the rate constants for internal conversion and photoisomerization show an exponential dependence on the energy of the absorption transition (Fig.…”