Two-Photon-Absorption Properties of Pyrene-Based Dipolar D-π-A Fluorophores

Hexa-Branched Nanographenes with Large Two-Photon Absorption

The conventional approach toward molecules with large two-photon absorption (TPA) involves donor-acceptor conjugation. Herein we show a new strategy involving the use of hexa-branched nanographenes. We synthesized two hexa-branched nanographenes, one with six benzoaceanthrylene arms fused to the coronene core and the other with six pyrenyl arms fused to the coronene core. Neither of these hexa-branched nanographenes has a donor-acceptor structure, yet they exhibited high TPA values of 3.6 × 103 and 1.9 × 104 GM, respectively, which are the highest values recorded for heteroatom-free hydrocarbon molecules. Theoretical analysis suggests that the fused branched structures are responsible for the large TPA cross-section. These findings illustrate the importance of the topology of the fused conjugated skeleton in TPA and provide an alternative structural design toward large TPA.

Nonlinear optical properties and optimization strategies of D-π-A type phenylamine derivatives in the near-infrared region

Modifying simple molecular structures to significantly improve nonlinear optical (NLO) performance is a primary prerequisite for scientific research. Based on the four phenylamine derivatives reported in previous studies, we designed four organic nonlinear molecules by changing the acceptor group and π-linker. (Time-dependent) density functional theory (DFT/TD-DFT) was performed on molecular geometry optimization, the contribution of π electrons to the bond order, linear and two-photon absorption (TPA) spectra, the intra-molecular charge transfer matrix (CTM), and NLO coefficients. These aspects were considered to analyze in detail how the structural modification of acceptors and π-linkers affects NLO characteristics. The three modification methods were: adding a carbonyl group at the junction of the π-linker and the acceptor group, adding a carbonyl group and a nitrogen atom to the acceptor group, and replacing the quinolinone with a pyrenyl group as the π-linker. The latter two methods can significantly reduce the excitation energy and enhance the intensity of intra-molecular charge transfer during the two-photon transition. The maximum TPA cross-sections and wavelengths of the designed molecules are DPPM (84722.6 GM, 815.7 nm) and DDPM (21600.6 GM, 781.3 nm). These two molecules have large TPA cross-sections in the near-infrared region, which renders them as possible NLO materials with broad application prospects.

One-Pot Synthesis of Pyreno[2,1-b]furan Molecules with Two-Photon Absorption Properties

The development of large π-conjugated polycyclic heteroaromatic materials is of immense interest, both in the academic as well as the industrial community. Herein, we present the efficient one-pot synthesis of novel pyreno[2,1-b]furan molecules from a newly designed intermediate, which display intense green emission (505-516 nm) in solution and a large red shift emission (625-640 nm) in the solid state, because of strong π-π stacking. More interestingly, the compounds exhibit novel two-photon absorption (TPA) properties, and the TPA cross-section (δ) value was increased to 533 GM by regulating the electronic effects of the substituents of the pyreno[2,1-b]furan molecules. This study not only offers a facile strategy for constructing new pyrene-fused luminescence materials with two-photon absorption properties but also provides a new chemical intermediate that opens up a new pathway to advanced materials.

Structure-controlled intramolecular charge transfer in asymmetric pyrene-based luminogens: synthesis, characterization and optical properties

Four asymmetric D–A type pyrene-based luminogens with tunable optical properties were synthesized, which provide an efficient strategy to achieve pyrene-based full-color photoelectric materials.

Two-photon absorption and two-photon-induced isomerization of azobenzene compounds

The process of two-photon-induced isomerization occurring in various organic molecules, among which azobenzene derivatives hold a prominent position, offers a wide range of functionalities, which can be used in both material and life sciences. This review provides a comprehensive description of nonlinear optical (NLO) properties of azobenzene (AB) derivatives whose geometries can be switched through two-photon absorption (TPA). Employing the nonlinear excitation process allows for deeper penetration of light into the tissues and provides opportunities to regulate biological systems in a non-invasive manner. At the same time, the tight focus of the beam needed to induce nonlinear absorption helps to improve the spatial resolution of the photoinduced structures. Since near-infrared (NIR) wavelengths are employed, the lower photon energies compared to usual one-photon excitation (typically, the azobenzene geometry change from trans to cis form requires the use of UV photons) cause less damage to the biological samples. Herein, we present an overview of the strategies for optimizing azobenzene-based photoswitches for efficient two-photon excitation (TPE) and the potential applications of two-photon-induced isomerization of azobenzenes in biological systems: control of ion flow in ion channels or control of drug release, as well as in materials science, to fabricate data storage media, optical filters, diffraction elements etc., based on phenomena like photoinduced anisotropy, mass transport and phase transition. The extant challenges in the field of two-photon switchable azomolecules are discussed.

Volatilised pyrene: A phase 1 study demonstrating a new method of visualising fingermarks with comparisons to iodine fuming

Pyrene is a fluorescent polycyclic aromatic hydrocarbon that can be volatilised under mild conditions. When fumed, pyrene is rapidly absorbed into the sebaceous residues of fingermarks, enabling their fluorescent visualisation upon excitation with ultraviolet radiation. This new means of fluorescent fingermark detection is more sensitive than the non-fluorescent iodine fuming approach for nonporous surfaces. This is demonstrated here in a phase 1 study using split-print comparisons on metal and glass surfaces. Pyrene-treated fingermarks also retain the volatile fluorophore for comparably long time periods relative to iodine fuming (in the order of hours). The phase 1 study comprised four donors, and 80 natural fingermarks that were grouped into two time periods; aged 24h and 1 week. Iodine fuming was chosen as a reference to showcase the effectiveness of pyrene given it is the most closely-related chemical fuming method in routine use. This study demonstrates that pyrene fuming increases the quantity and quality of fingermark visualisations relative to iodine fuming, and is free of many of the latter method's drawbacks. Preliminary results shown here also show the effectiveness of pyrene fuming on highly patterned surfaces, and its compatibility with the use of gelatine lifters. Pyrene fuming is thus easy to effect, low-cost, and shows great promise as a new means of visualising fingermarks on non-porous surfaces.