Femtosecond Spectroscopy and Nonlinear Optical Properties of aza-BODIPY Derivatives in Solution.

The fast relaxation processes in the excited electronic states of functionalized aza-boron-dipyrromethene (aza-BODIPY) derivatives (1-4) were investigated in liquid media at room temperature, including the linear photophysical, photochemical, and nonlinear optical (NLO) properties. Optical gain was revealed for nonfluorescent derivatives 3 and 4 in the near infrared (NIR) spectral range under femtosecond excitation. The values of two-photon absorption (2PA) and excited-state absorption (ESA) cross-sections were obtained for 1-4 in dichloromethane using femtosecond Z-scans, and the role of bromine substituents in the molecular structures of 2 and 4 is discussed. The nature of the excited states involved in electronic transitions of these dyes was investigated using quantum-chemical TD-DFT calculations, and the obtained spectral parameters are in reasonable agreement with the experimental data. Significant 2PA (maxima cross-sections ∼2000 GM), and large ESA cross-sections ∼10-20  m2 of these new aza-BODIPY derivatives 1-4 along with their measured high photostability reveal their potential for photonic applications in general and optical limiting in particular.

Aza-BODIPY-based Fluorescent and Colorimetric Sensors and Probes.

Aza-boron-dipyrromethenes (Aza-BODIPYs) represent an important class of chromophores absorbing and emitting in the near-infrared (NIR) region. They have unique optical and electronic features and higher physiological and photo stability than other NIR dyes. Especially after the development of facile synthetic routes, Aza-BODIPYs have become indispensable fluors that can find various applications ranging from chemosensors, bioimaging, phototherapy, solar energy materials, photocatalysis, photon upconversion, lasers, and optoelectronics. Herein, we review Aza-BODIPY based fluorescent and colorimetric chemosensors. We show the potential and untapped toolbox of Aza-BODIPY based fluorescent and colorimetric chemosensors. Hence, we divide the fluorescent and colorimetric chemosensors and probes into five sections according to the target analytes. The first section begins with the chemosensors developed for pH. Next, we discuss Aza-BODIPY based ion sensors, including metal ions and anions. Finally, we present the chemosensors and probes concerning reactive oxygen (ROS) and nitrogen species (RNS) along with biologically relevant species in the last two sections. We believe that Aza-BODIPYs are still in their infancy, and they have a promising future for translation from the bench to real biomedical and materials science applications. After two decades of intensive research, it seems that there are many more to come in this already fertile field. Overall, we hope that future work will further expand the applications of Aza-BODIPY in many areas.

A novel near-infrared-emitting aza-boron-dipyrromethene-based remarkable fluorescent probe for Hg2+ in living cells.

A new near-infrared (NIR)-emitting aza-boron-dipyrromethene dye with two electron-donating amino groups at 1- and 7-positions has been prepared via several steps of reactions. This probe showed a NIR absorption at 748 nm with an obvious shoulder peak at 634 nm in CH3CN/H2O. Interestingly, a NIR fluorescence emission at 843 nm was observed with a large Stokes shift of 95 nm. This novel NIR-emitting aza-boron-dipyrromethene dye was further investigated as a Hg2+-sensing fluorescent probe, which selectively bound to Hg2+, showing a blue-shifted and sharp absorption band at 695 nm with the disappearance of the shoulder peak at 634 nm. Correspondingly, the color change could be easily seen from blue to green. Interestingly, the emission exhibited an absolutely "turn-on" peak at 725 nm with a significant blue shift by 118 nm (from 843 to 725 nm), due to the efficient inhibition of the intramolecular-charge-transfer process arising from two amino groups. This probe was finally introduced to Hela cells, showing a "OFF-ON" NIR emission upon exposure to Hg2+. The overall results confirmed that this novel NIR-emitting aza-boron-dipyrromethene fluorescent probe with a large Stokes shift could serve as a colorimetric and fluorescent "turn-on" sensor for Hg2+ in both solutions and living cells.