Fluorescence properties of aza-helicenium derivatives for cell imaging

Functionalized cationic [4]helicenes with unique tuning of absorption, fluorescence and chiroptical properties up to the far-red range

“… 2 Such photophysical characteristics have triggered applications in (polarized) blue light emitting diodes for instance 3 and to a lesser extent in the field of bio-imaging. 4 Accessing the red spectral region (620–750 nm) is essential for applications in microscopy and chemical biology in particular, and this remains a challenge for organic helicenes. 5 In fact, only a few cationic aza derivatives, e.g.…”

Functionalization of nanostructured gold substrates with chiral chromophores for SERS applications: The case of 5‐Aza[5]helicene

“…In addition to SERS, we have also investigated the fluorescence behavior of the helicene‐functionalized plasmonic substrates, motivated by the appealing photophysical properties reported for these systems . As shown in Figure , by adopting a second experimental setup, with exciting laser radiation within the visible range (458 nm), we can collect the fluorescence originating from the helicene layer anchored on the gold surface, while no SERS peaks are observed.…”

“…In addition to SERS, we have also investigated the fluorescence behavior of the helicene-functionalized plasmonic substrates, motivated by the appealing photophysical properties reported for these systems. 22,23 As shown in Figure 6, by adopting a second experimental setup, with exciting laser radiation within the visible range (458 nm), we can collect the fluorescence originating from the helicene layer anchored on the gold surface, while no SERS peaks are observed. This happens because the 458-nm excitation lies far away from the plasmon resonance of the gold substrates, which have been optimized for SERS action with 785-nm excitation, 43,44 while being able to excite the 5-aza [5]helicene moiety, enabling the fluorescence peak observed at 517 nm ( Figure 6).…”

“…They may find useful applications in the biotechnological field as enantioselective fluorescent sensors because water‐soluble quaternary N ‐methyl[5]helicenium salts have been extensively tested for DNA binding, showing the ability to chromatically distinguish different subcellular compartments and to follow the cell uptake process . Interestingly, N ‐methyl[5]helicenium iodide, despite its fluorescence, displays a strong SERS activity in ordinary Lee‐Meisel silver colloids, as illustrated in Figure . Actually, N ‐methyl‐5‐aza[5]helicenium iodide shows a fluorescence emission peak at 503 nm, with 270‐nm excitation line, but the presence of the colloids enables fluorescence quenching, thus allowing the measurement of an intense SERS signal.…”

Quantum Mechanics Calculations, Basicity and Crystal Structure: The Route to Transition Metal Complexes of Azahelicenes

“…This is related on the one hand to their extended conjugated system, which imparts them large conductivity and polarizability, with high-order susceptibility term, and as a consequence a strong luminescence [ 5 , 6 ]. On the other hand, their intrinsic chirality due to helicity, with extremely high optical rotation, could be exploited both in the field of non-linear optics and for interactions with biomolecules [ 7 , 8 ]. Azahelicenes can aggregate into relatively stable supramolecular structures (π-stacking, polar interactions); in addition they exhibit a remarkably long triplet state lifetime [ 9 ].…”