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.

Synthesis and photophysical properties of nitrated aza-BODIPYs

A series of nitrated aza-BODIPYs on the 2- and 6-positions were regioselectively synthesized and their photophysical properties were examined.

Near-infrared dyes for two-photon absorption in the short-wavelength infrared: strategies towards optical power limiting

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.

Carbazole Substituted BODIPYs

Difluoroboron-dipyrromethenes (BODIPYs) are highly popular fluorescent dyes with applications as NIR probes for bioimaging, fluorescent tags/sensors and as photosensitizers in cancer therapy and organic photovoltaics. This review concentrates on the synthesis and spectral properties of BODIPY dyes conjugated with carbazole heterocycle. The carbazole is an electron rich tricyclic compound and due to its excellent electronic properties, it is extensively used in the production of electroluminescent materials and polymers. This review highlights the recent progress made on the series of BODIPY derivatives containing carbazole ring at alpha, beta, and meso-positions of the BODIPY skeleton. Carbazole based hybrid BODIPYs, carbazole linked aza-BODIPYs and carbazole-fused BODIPYs are also discussed.

NLOphoric benzyl substituted BODIPY and BOPHY: A comprehensive linear and nonlinear optical study by spectroscopic, DFT and Z-scan measurement

BOPHY (BPY) and BODIPY (BDY) dye bearing benzyl group (Bn) at 4,4' and 2,6 position respectively were synthesized and characterized. The fluorescence decay measurements were performed which reveal that benzyl BOPHY (Bn-BPY) has shorter fluorescence lifetime compared to benzyl BODIPY (Bn-BDY). The difference in transition dipole moment is found to be 6.93 and 11.3 D for Bn-BDY and Bn-BPY respectively in toluene. The molecular electrostatic potential (MEP) plot shows Bn-BDY is more polarised compared to Bn-BPY. The nonlinear optical (NLO) property was evaluated using Z-scan measurement. The molecular electronic arrangement of Bn-BPY significantly affects the nonlinear absorption properties resulting into reverse saturable absorption (nonlinear absorption coefficient β = 0.256 × 10^-11 m/W). In contrast, the Bn-BDY displays saturable absorption character. The calculated third-order nonlinear susceptibility χ⁽³⁾ value is 12.23 × 10^-13 esu and 2.49 × 10^-13 esu for Bn-BDY and Bn-BPY respectively. The power limiting behaviour of Bn-BPY displays limiting threshold energy around 70 Jcm^-2 with clamped output at ~35 Jcm^-2.

Non-linear optical response of meso hybrid BODIPY: Synthesis, photophysical, DFT and Z scan study

Hybrid meso BODIPY dyes are synthesized and their linear and non-linear optical properties are studied. Time-resolved fluorescence lifetime decay is found to be identical for all dyes irrespective of meso substituents. The Z-scan experiment performed to calculate the nonlinear absorption coefficient (β) and third-order nonlinear susceptibility (χ³). Global hybrid (B3LYP and BHHLYP) and range-separated hybrid (CAM-B3LYP) functional with the basis set 6-311++G(d,p) was employed to determine the theoretical linear and non-linear optical properties. The computed β₀ value of all the three dyes was found to be superior to that of urea (βo = 0.371 × 10^-30 esu). Introduction of meso substituent directly affects the polarizability and second-order hyperpolarizability of the dyes. Thermal and reorientational effect of the investigated NLOphoric dyes were studied.

Two-photon absorption of BF2-carrying compounds: insights from theory and experiment

This communication presents a structure-property study of a few novel pyridine-based difluoroborate compounds with a N-BF₂-O core, which exhibit outstanding fluorescence properties. To exploit their potential for two-photon bioimaging, relationships between the two-photon action cross section and systematic structural modifications have been investigated and unravelled.

Interplay of twist angle and solvents with two-photon optical channel interference in aryl-substituted BODIPY dyes

Channel interference plays a crucial role in understanding the physics behind multiphoton absorption processes. In this work, we study the role of channel interference and solvent effects on the two-photon absorption in aryl-substituted boron dipyrromethene (BODIPY) dyes, a class of intramolecular charge-transfer (ICT) molecules. For this purpose, we consider fourteen dyes of this class with various donor/acceptor substitutions at the para position of the phenyl ring and with or without methyl (-CH₃) substitution on the BODIPY moiety. The presence of a methyl group on the BODIPY moiety affects the dihedral angle significantly, which in turn affects the one- (OPA) and two-photon absorption (TPA) properties of the molecules. Among the molecules studied, the one having the strong electron-donating dimethylamino group and no methyl substitution at the BODIPY moiety is found to have the highest TPA cross section. Our few-state model analysis shows that the large TPA activity of this molecule is due to the all positive contributions from different channel interference terms. Change in dielectric constant of the medium is found to have a profound impact on both the magnitude and sign of the channel interference terms. The magnitude of destructive channel interference gradually decreases with decreasing solvent polarity and becomes constructive in a low-polarity solvent. We also study the effect of rotating the phenyl ring with respect to the BODIPY moiety on the TPA activity. In the gas phase and in different solvents, we found that channel interference is changed from destructive to constructive on twisting the molecule. These results are explained by considering different dipole-, energy- and angle-terms appearing in the expression of a two-state model.

A theoretical investigation of the two-photon absorption and fluorescent properties of coumarin-based derivatives for Pd2+ detection

Two-photon fluorescent probes that can detect Pd²⁺ according to the “turn-on” fluorescence signal are reported.

Two-photon absorption in a series of 2,6-disubstituted BODIPY dyes

We report on the two-photon absorption spectra of a series of 2,6-disubstituted BODIPY dyes.

Synthesis, screening and sensing applications of a novel fluorescent probe based on C-glycosides

A novel water soluble fluorescent probe based on C-glycoside with an aromatic aldehyde unit has been synthesized and its UV/Vis and fluorescence spectra, aggregation and disaggregation with bovine serum albumin were studied.

Nonlinear refraction and absorption activity of dimethylaminostyryl substituted BODIPY dyes

Optical and nonlinear optical properties of difluoroboradiazaindacene (BODIPY) models with attached dimethylaminostyryl substituents were studied.

Azadipyrromethenes: from traditional dye chemistry to leading edge applications

The journey of azadipyrromethenes from accidental dye chemistry to a compound class with widely applicable near infrared photophysical properties is documented.

A theoretical study of a series of novel two-photon nitric oxide (NO) fluorescent probes based on BODIPY

The PET probing mechanism and intrinsic two-photon absorption properties of the studied molecules are rationally explained.

Effect of alkyl substituents in BODIPYs: a comparative DFT computational investigation

A detailed computational investigation encompassing the effects of alkyl groups on the structural and electronic properties of BODIPY dyes is presented.

Nonlinear optical properties of multipyrrole dyes

The nonlinear optical properties of a series of pyrrolic compounds consisting of BODIPY and aza-BODIPY systems are investigated using 532 nm nanosecond laser and the Z-scan technique. Results show that 3,5-distyryl extension of BODIPY to the red shifted MeO₂BODIPY dye has a dramatic impact on its nonlinear absorption properties changing it from a saturable absorber to an efficient reverse saturable absorbing material with a nonlinear absorption coefficient of 4.64 × 10^-10 m/W. When plotted on a concentration scale per mole of dye in solution MeO₂BODIPY far outperforms the recognized zinc(II) phthalocyanine dye and is comparable to that of zinc(II) tetraphenylporphyrin.