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

Abstract

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.

Tuning the Photophysical Properties of Aza‐BODIPYs in the Near‐Infrared Region by Introducing Electron‐Donating Thiophene Substituents

“…We then extended this approach to the tetra-brominated reagents 7 and 8, prepared via an additional bromination of intermediates 1 and 2 using TBABr 3 (Scheme 2). [26,34] Following the above-described procedure, 7 and 8 were engaged in tetra-Stille coupling reactions using donor D 1 and tetrakis (triphenylphosphine) palladium to afford the targeted dipyrromethene 9 and 10. Intermediate 9 was obtained with a high yield (80 %) indicating that the additional substitution on the side positions does not alter the reactivity.…”

“…More recently, it has been proposed to replace the phenyl substituents at positions 1,7 with benzothiazoles (BTDs) in order to maximize the ICT. Those BTD‐substituted aza‐BODIPYs are among the most red‐shifted fluorescent dyes reported to date [25,26] . However, in spite of remarkable OPL efficiency in solution in the SWIR, [26] these molecules could not be used as solid optical limiters, due to their impossible incorporation into sol‐gel matrices.…”

“…Those BTD‐substituted aza‐BODIPYs are among the most red‐shifted fluorescent dyes reported to date [25,26] . However, in spite of remarkable OPL efficiency in solution in the SWIR, [26] these molecules could not be used as solid optical limiters, due to their impossible incorporation into sol‐gel matrices. Another strategy consists in tuning the spectroscopic properties of aza‐BODIPY dyes by replacing the phenyl moieties with thiophene, which was found to result in a bathochromic shift of the absorbance and an increase of the molar extinction coefficient [27,28] .…”

Ultrafast Nonlinear Optical Activities of Near-Infrared Aza-BODIPY Derivatives

“…Boron-dipyrromethene (BODIPY) belongs to a family of organoboron compounds, which displays good photostability and excellent NLO properties [24][25][26]. As various BODIPY derivatives, Aza-BODIPY derivatives possess superior optical properties, including red-shifted spectra and high Disclaimer/Publisher's Note: The statements, opinions, and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s).…”

Asymmetric AZA-BODIPY with Optical Gain in the Near-Infrared Region

“…In order to red-shift the spectral properties of BODIPY, in 2002 Killoran et al [ 28 ] proposed the replacement of the carbon in position 8, or the meso position, with a nitrogen with the formation of a C=N linkage, which is isoelectronic with the C=CH group but has different geometric and electronic requirements [ 29 , 30 ]. This modification led to the birth of a new family of materials, known as AZA-BODIPY ( Figure 1 a), that retain the main characteristics of the BODIPY-based molecules, but show a markedly red-shifted absorption and emission and specific linear photophysical and nonlinear optical (NLO) properties [ 31 ]. Their use is a subject of great interest for photonics applications, including important multidisciplinary areas such as fluorescence bioimaging [ 32 , 33 ] and organic photovoltaics [ 34 ].…”