Alexander Baev

Synthesis and nanoparticle encapsulation of 3,5-difuranylvinyl-boradiaza-s-indacenes for near-infrared fluorescence imaging

We report molecular design, synthesis, and photophysical study of a series of near-infrared absorbing and fluorescing dyes, 3,5-difuranylvinyl-boradiaza-s-indacenes, bearing various 5-membered heteroaromatic heads at the 8-position (FBs). The correlation between the molecular structure and the spectral shift has been studied by quantum chemical calculations at various levels (B3LYP/6-31G*, HF/6-31G* and HF/PM3), which conclude that the planarity determined by the bulkiness of the head unit controls the optical bandgap of FBs, by energetically affecting the lowest unoccupied molecular orbital (LUMO) rather than the highest occupied molecular orbital (HOMO). We also show that incorporation of heavy atoms increased the capability of singlet oxygen generation as a result of enhanced intersystem crossing, which makes FBs potentially useful for near-infrared photodynamic therapy. In vitro near-infrared fluorescence imaging of live tumor cells has been demonstrated through a nanocarrier approach, by encapsulating one of the FB dyes in a stable aqueous formulation of organically modified silica nanoparticles which retains the fluorescence efficiency of the hydrophobic dye in water.

Ab initio studies of two-photon absorption of some stilbenoid chromophores

Two-photon absorption of a series of donor-acceptor trans-stilbene derivatives is studied by means of density functional theory applied to second-order response function. Several important issues in modeling are highlighted which must be addressed for a reliable reproduction of the experimental results. It is evident that the correct order of magnitude of calculated two-photon absorption cross sections can only be obtained if proper account is taken of vibrational broadening of the absorption profiles. A comparison of the theoretical results with the experimental ones indicates that the computed two-photon absorption cross sections are in rough agreement with our previous report, although the observed systematic increase of the cross sections with the electron acceptor strength is not well reproduced. It is suggested that this disagreement may be due not only to the deficiencies of the computations but also to a variety of factors contributing to the experimental value of the effective two-photon absorption cross section, which are not taken into account in the ab initio calculations.

Molecular nonlinear optics: recent advances and applications

The field of nonlinear optics continues to evolve and impact many fields and particularly has promising applications in the biomedical field. Furthermore, a major application, all-optical switching, has still not been realized because of the lack of a suitable material with high nonlinear figure of merit. This review focuses specifically on molecular materials that provide an opportunity for optimization of optical nonlinearity at two levels: microscopic and bulk. We present essential physics at these two levels and describe how the relationship between microscopic and bulk levels can be exploited to design new materials with enhanced optical nonlinearity. In this context, we introduce recent advances in multiscale modeling. The emphasis in this review is placed on third-order optical nonlinearity that governs all-optical processes. We discuss the current status of nonlinear optical studies on new molecular systems and the challenges to be met. This review covers newly emergent promising directions, together with their most impactful applications, and thus is beyond the comprehensive account of all the progress that has been made in the area of molecular nonlinear optics. Therefore, novel directions for enhancing molecular nonlinearities are presented, which include twist-motif chromophores, synergistic coupling between bond length alternation and high density of states, microscopic cascading, hybridization of states, etc. We then present some specific, promising nonlinear media. In this context, metamaterials and metasurfaces are also discussed, as they play an important role in the enhancement of nonlinearities and light manipulations. Another new direction covered is chiral nonlinearity. Finally, we present some selected major applications of nonlinear optics, specifically in optical signal processing, optical limiting, biophotonics, and upconversion random lasing. The review concludes with the authors’ views on the future perspective.

Manipulating nanoscale interactions in a polymer nanocomposite for chiral control of linear and nonlinear optical functions.

The design, synthesis, and supramolecular organization of a nanocomposite in which nanoscale excitonic interactions between quantum dots and the chiral polymer dramatically enhance the optical activity is reported. This material is highly suitable for application in the emerging field of chiral photonics.

Photothermal-reaction-assisted two-photon lithography of silver nanocrystals capped with thermally cleavable ligands

We report an alternative approach to produce micropatterns of metallic nanoparticles using photothermal-reaction-assisted two-photon direct laser writing. The patterns are achieved using a facile surface treatment of silver nanoparticles (Ag NPs) functionalized with thermally cleavable ligands; N-(tert-butoxycarbonyl)-L-cysteine methyl ester. The ligand cleavage initiated by pulsed laser-induced thermal reaction results in a significant change in dispersiblility of the nanocrystals, thereby enabling a solvent-selective development process after photopatterning. We demonstrated that Ag NP patterns with submicron linewidths can be achieved using near infrared pulsed laser illumination.

Chiral polymer photonics

Chiral photonics concerns enantio-selective polarization control of linear and nonlinear optical functions. However, natural chiral media do not exhibit strong chiro-optic response. In our laboratory, guided by multiscale modeling, we have developed new chiral polymers and their nanocomposites. Their optical and magneto-optic activity can be amplified by manipulating supramolecular organization and by introducing strong coupling with plasmonic/excitonic, as well as paramagnetic nanoinclusions. We present here an account of our recent progress in the design, development and characterization of these materials that can have a potentially huge technological impact by allowing ultrathin, flexible, low-cost devices such as polarizers, optical isolators, optical magnetometers.

Coupled-plasmon induced optical nonlinearities in anisotropic arrays of gold nanorod clusters supported in a polymeric film

Exploiting a giant plasmonic field enhancement in an anisotropic array of gold nanorod clusters in a polyvinyl alcohol (PVA) film, we have experimentally studied its nonlinear absorptive and refractive response. Gold nanorod cluster-PVA nanocomposites were prepared, and the uniaxial alignment was obtained by mechanically stretching the films. Using the Z-scan method and excitation with 100 fs pulses at 800 nm, intensities up to 70 GW/cm2 at 20 Hz, saturation of both nonlinear absorption and nonlinear refraction were observed. The results are discussed in light of a plasmonic effect arising from the gold nanorod clusters aligned in the stretched polymeric matrix. A polarization dependent sign reversal of the nonlinear refraction was observed, which can find applications in nanoscale photonic devices. The results are supported by finite element analysis of local electric field distribution in the arrays of gold nanorod clusters.