The recent advances in the field of two-photon absorbing chromophores in the short-wavelength infrared spectral range (SWIR 1100–2500 nm) are summarized, highlighting the development of optical power limiting devices in this spectral range.

Straightforward synthesis and resolution of a series of chiral fluorescent macrocycles are presented, together with their electronic circular dichroism (ECD), strong excimer fluorescence (EF, λ 300 to 650 nm) and allied highly circularly polarized luminescence (CPL, g_lum up to 1.7 × 10⁻²). The ECD, EF and CPL responses are strongly affected by the presence of metal ions (Na⁺, Ba²⁺) thanks to deep conformational changes. While ECD signals can be almost completely reversibly inverted upon the complexation/decomplexation of metal ions in a typical binary response, CPL signals are reversibly quenched concomitantly. The designed macrocycles display thus a remarkable combination of both +/− ECD and on/off CPL reversible switching.

Unprecedented regioselective post-functionalization of racemic and enantiopure cationic diaza [4]helicenes is afforded. The peripheral auxochrome substituents allow a general tuning of the electrochemical, photophysical and chiroptical properties of the helical dyes (26 examples). For instance, electronic absorption and circular dichroism are modulated from the orange to near-infrared spectral range (575–750 nm), fluorescence quantum efficiency is enhanced up to 0.55 (631 nm) and circularly polarized luminescence is recorded in the red (|g_lum| ∼ 10⁻³).

The long luminescence lifetime of lanthanide based bioprobes is a great advantage for their specific detection in autofluorescent or labelled cells and tissues. It is also a valuable tool for sensing the physicochemical microenvironment and molecular interactions by Förster resonance energy transfer (FRET). However, standard confocal and multiphoton laser scanning microscopes are not adapted for imaging with such temporal resolution, because the typical pixel dwell time is too short compared to the luminescence lifetime. We show that the rapid sampling rate and laser control of a usual confocal microscope can instead be used for precise measurement of long lifetime decays (μs to ms range). Furthermore, both raster- and line-scanning microscopes can specifically detect long luminescence signals in the time-gated mode by shifting the pinhole or the confocal slit in the lagging direction. We characterized the subcellular localization and accurately measured the millisecond luminescence lifetimes of the benchmark two-photon europium probe [Na]₃[EuL^1G₃], and specifically imaged this label in the presence of short-lived fluorescent species. Fine variations of the luminescence lifetime of this lanthanide complex were revealed and mapped in cells in the presence of a FRET acceptor, allowing quantification of the FRET efficiency independently of donor concentration. These results demonstrate a high and yet unexploited potential of quantitative confocal and multiphoton microscopy for time-gated and lifetime imaging of lanthanide-based biological sensors.

The chiroptical switching properties of a readily accessible and water-soluble diaza [4]helicene are disclosed.