Effects of substituents in the polymethine chain on the photoprocesses in indodicarbocyanine dyes

Abstract

Hexamethylindodicarbocyanine perchlorate (1) and iodide (1') and five indodicarbocyanine derivatives (with substituents in the meso-position of the polymethine chain; R = CH, 2, C1 3, Br 4, CN 5 and 1,3,3-trimethylindoline-2-ethenyl 6) were studied by time-resolved spectroscopy in slightly and strongly polar solvents, where ion pairs with ClO,-are present and absent, respectively. The quantum yield of fluorescence at 24°C is Qf = 0.012 for 6 in ethanol and larger for 1-5. Qf increases markedly with decreasing temperature, approaching 0.7-0.9 at -196 "C. The fluorescence lifetime, e.g. typically zf = 3 ns in glassy ethanol, is correlated. trans + cis Photoisomerization occurs in virtually all cases. The quantum yield depends significantly on the medium and meso substituent; @t-+c is substantial for 2 and 3 in ethanol at 24°C and decreases with decreasing temperature. The initial rotation around one of the central double bonds in the excited singlet state is activated. At room temperature the lifetime of the observed cis form is in the ms range. No discernible effect of ion-pairing on the kinetic parameters of the thermal cis + trans reversion could be found in toluene. The triplet state of the six dyes was characterized by sensitization; it plays a (minor) role on direct excitation only for 4 or in the presence of a heavy-atom solvent. c H3 C2H5 Chart 1

Ultra-stable organic fluorophores for single-molecule research

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On the Mechanisms of Cyanine Fluorophore Photostabilization

“…Because the formation of triplet states of Cy5 is inefficient (triplet quantum yield < 0.003) upon direct excitation, 10 a triplet sensitizer was employed to more efficiently populate the Cy5 triplet state ( 3 Cy5*) through an energy transfer mechanism (eq 1). Benzophenone (BP) was selected as a sensitizer, because of its high triplet quantum yield and higher triplet energy (289 kJ/mol) 11 compared to Cy5 (154 kJ/mol) 12 .…”

“…In line with this assignment, other cyanine dyes also show triplet state absorption at 700 nm. 10,13 Conversely, the cis -conformation of ground state Cy5 is also known to absorb in this spectral region. 10,13,14 However, the observed quantitative quenching of the transient by O 2 demonstrates that the contribution of the ground state cis -conformer (which is not quenched by O 2 ) to the transient absorption at 700 nm is negligible.…”

Photophysical Studies of a New Water Soluble Indocarbocyanine Dye Adsorbed onto Microcrystalline Cellulose and beta-Cyclodextrin

“…Indocarbocyanine dyes, with different chain lengths of the central conjugated methine chain, are attractive mainly due to their ability to strongly absorb light from the blue to the near-infrared region [49]. Compared with other cyanine dyes, indocarbocyanine dyes have high solubility in solvents and have good thermal stability [50,51].…”