Effect of bromination on the optical limiting properties at 532 nm of BODIPY dyes with p-benzyloxystyryl groups at the 3,5-positions

Solvent effect, DFT and NLO studies of A-π-D-π-A and A-π-D-π-D push-pull chromophore of 1,2-diazepin-4-ol based derivatives with optical limiting application

The nonlinear optical properties of push-pull chromophores, namely (E)-7-(4-bromophenyl)-2,5-bis(4-nitrophenyl)-3,4,5,6-tetrahydro-2H-1,2-diazepin-4-ol (A-π-D-π-A) and (E)-7-(4-bromophenyl)-5-(4-nitrophenyl)-2-phenyl-3,4,5,6-tetrahydro-2H-1,2-diazepin-4-ol (A-π-D-π-D), have been investigated using the z-scan technique. NMR, FT-IR, and UV-visible spectral analysis have been performed. The results were compared with density functional theory calculations employing the B3LYP/6-311++G (d, p) basis set. Geometry optimization, frontier molecular analysis, and TD-DFT calculations were conducted in various solvent environments to elucidate solute-solvent interactions. Gaussian 09 software was employed for natural bond orbital analysis, natural population analysis, and molecular electrostatic potential exploration. This comprehensive approach provides insights into the molecular structure and electronic properties of the investigated chromophores, shedding light on their potential applications in nonlinear optics. Normal coordinate analysis using the MOLVIB software has been used to assign the vibrational mode unambiguously. Theoretical second-order hyperpolarizability was computed, and NLO investigations have been employed to determine the second-order hyperpolarizability in both the polar and non-polar solvents. Further, the optical limiting capability was also examined.

BODIPY dyes for optical limiting applications on the nanosecond timescale

Since 2017, the Institute for Nanotechnology Innovation at Rhodes University has studied the optical limiting properties of boron dipyrromethene (BODIPY) dyes with respect to high-intensity nanosecond timescale laser pulses. Concerns over the irresponsible use of laser pointers in the context of aviation safety have provided a need for materials that can readily transmit light under ambient conditions while rapidly attenuating intense incident laser pulses. The structural flexibility of the BODIPY chromophore facilitates the red shift of the main BODIPY spectral band that typically lies at ca. 500 nm to the red end of the visible and the near-infrared through the introduction of vinylene groups at the 3,5-positions or an aza-nitrogen atom. Research carried out in this context is described, and possible future directions are discussed.

Enhanced NLO response and switching self-focussing in benzodiazepine derivative with -NO2 and -Br substitution

Optoelectronic and the cubic nonlinear optical properties of 4-(4-Bromophenyl)-2-(4-nitrophenyl)-2, 3-dihydro-1H-1, 5-benzodiazepine have been studied. Z-scan technique was used for the third-order nonlinear optical measurements namely, nonlinear absorption, nonlinear refraction, and optical power limiting behaviour employing an Nd: YAG laser of 532 nm wavelength having 5 ns Gaussian pulses. B3LYP/6-311 ++ G (d, p) level of theory was employed for structural optimization, vibrational wavenumber, frontier molecular orbitals, natural bond orbital and population analysis. The MOLVIB programme was used to perform unambiguous vibrational assignments based on potential energy distribution values acquired from normal coordinate analysis. B3LYP and CAM-B3LYP hybrid functions have been employed at the DFT level to calculate the theoretical second-order hyperpolarizability. The substitution of -NO2 and -Br in this benzodiazepine compound enhances the second-order hyperpolarizability (γ) to the order of 10-34 esu and, switching of self-defocussing to self-focussing phenomenon. The HOMO-LUMO and optical band gap analysis illustrates that polarizing nature of the molecule vary with substituents. The obtained results indicate that this compound has potential applications in optoelectronics and photonics.

New insights into quantifying the solvatochromism of BODIPY based fluorescent probes

A simple semiempiric phenomenological approach is developed for quantifying the solvent effect on the absorption and emission properties of BODIPYs. It is based on a new rule describing the linear relationship between the difference (Stokes shift) and the sum (double Gibbs free energy of electron transfer) for absorption and emission wavenumbers derived from a combination of solvent functions of Liptay theory. This rule is correspondent to changes of dipole moments in the ground and excited states. High reliability and advantages of the developed approach in comparison with traditional methods of the analysis of the solvatochromism based on Dimroth-Reichard and Lippert-Mataga solvent scales are illustrated for selected BODIPYs exhibiting positive, negative, and near-zero solvatochromism.

Optical limiting properties of D-π-A BODIPY dyes in the presence and absence of methyl groups at the 1,7-positions

The optical limiting properties of three meso-pentafluorophenylstyrylBODIPY dyes are investigated in the presence and absence of methyl groups at the 1,7-positions that hinder free rotation of the meso-aryl group. Pentafluorophenyl groups are introduced at the meso-position, while 4-diethylaminostyryl groups are introduced at the 3- and/or 5-positions to form dyes with strong donor-[Formula: see text]-acceptor (D-[Formula: see text]-A) properties to enhance the dipole moment of the molecule. Favorable optical limiting properties are obtained for all three dyes, with the highest second-order hyperpolarizability value obtained for a monostyryl dye with no methyl groups at the 1,7-position. Bromination at the 2,6-positions of a 1,7-methyl substituted dye is found to result in second-order hyperpolarizability that is an order of magnitude lower than that calculated for the analogous non-halogenated dye.

Photodynamic activity of 2,6-diiodo-3,5-dithienylvinyleneBODIPYs and their folate-functionalized chitosan-coated Pluronic® F-127 micelles on MCF-7 breast cancer cells

A 2,6-diiodo-3,5-dithienylvinyleneBODIPY dye was prepared and encapsulated with folate-chitosan capped Pluronic[Formula: see text] F-127 to provide drug delivery systems for photodynamic therapy (PDT). Moderately enhanced singlet oxygen quantum yields were observed for the dye encapsulation complexes in water. The in vitro dark cytotoxicity and photodynamic activity were investigated on the human breast adenocarcinoma (MCF-7) cell line. Minimal dark cytotoxicity was observed for the BODIPY dyes in 5% DMSO and when encapsulated in folate-functionalized chitosan-coated Pluronic[Formula: see text] F-127 micelles, since the cell viability values are consistently greater than 80% over the 0-40 [Formula: see text] concentration range. Upon irradiation of the samples, significant cytocidal activity was observed for the encapsulation complex of a 2,6-diiodo-8-dimethylaminophenyl-3,5-dithienylvinyleneBODIPY dye with less than 50% viable cells observed at concentrations [Formula: see text].

Optical Limiting and Femtosecond Pump-Probe Transient Absorbance Properties of a 3,5-distyrylBODIPY Dye

The optical limiting (OL) properties of a 3,5-di-p-benzyloxystyrylBODIPY dye with an p-acetamidophenyl moiety at the meso-position have been investigated by using the open-aperture Z-scan technique at 532 nm with 10 ns laser pulses. There is a ca. 140 nm red shift of the main spectral band to 644 nm relative to the corresponding BODIPY core dye, due to the incorporation of p-benzyloxystyryl groups at the 3,5-positions. As a result, there is relatively weak absorbance across most of the visible region under ambient light conditions. Analysis of the observed reverse saturable absorbance (RSA) profiles demonstrates that the dye is potentially suitable for use in optical limiting applications as has been reported previously for other 3,5-distyrylBODIPY dyes. Time-resolved transient absorption spectroscopy and kinetic studies with femtosecond and nanosecond scale laser pulses provide the first direct spectral evidence that excited state absorption (ESA) from the S1 state is responsible for the observed OL properties.

Optical limiting properties of BODIPY dyes substituted with styryl or vinylene groups on the nanosecond timescale

The results of recent studies on the optical limiting properties of BODIPY dyes at 532 and 1064 nm are described and compared. The optical limiting properties of novel 1,7-dimethyl-3,5-di-4-dihydroxyborylstyryl- and 3,5,7-tristyryl-1-methyl-BODIPY dyes were studied in CH2Cl2 and C6H6 and polystyrene thin films using the open aperture Z-scan technique at 532 nm with nanosecond laser pulses to provide an example of how the effective nonlinear absorption coefficient, the third order susceptibility, hyperpolarizability and limiting thresholds can be calculated.

An analysis of the photophysical and optical limiting properties of a novel 1,3,5-tristyrylBODIPY dye

The synthesis and characterization of a novel dibrominated 1,3,5-tristyrylBODIPY dye is reported, and its potential utility as a singlet oxygen photosensitizer and optical limiting material is assessed. The main spectral band lies in the therapeutic window, and there is a moderately high singlet oxygen quantum yield making the dye potentially suitable for use in biomedical applications and as an optical limiting dye at 532 nm. The optical limiting parameters are comparable to those reported previously for 3,5-distyrylBODIPYs, which suggests that mixtures of 3,5-distyryl and 1,3,5-tristyryl compounds that are formed in Knoevenagel condensation reactions could be used for this application. Theoretical calculations are used to assess the effect of 1,3,5-tristyryl substitution. A smaller red shift of the main spectral band is observed upon styrylation at the 1-position than is the case with the 3,5-positions due to there being smaller MO coefficients at this position, limiting the utility of this structural modification method for shifting the main BODIPY spectral band further into the therapeutic window.