Tzu-Chau Lin

Synthesis and Two‐Photon Absorption Property Characterizations of Small Dendritic Chromophores Containing Functionalized Quinoxaliniod Heterocycles

A series of star-shaped multi-polar chromophores (compounds 1-3) containing functionalized quinoxaline and quinoxalinoid (indenoquinoxaline and pyridopyrazine) units has been synthesized and characterized for their two-photon absorption (2PA) properties both in the femtosecond and the nanosecond time domain. Under our experimental conditions, these model fluorophores are found to manifest strong and wide-dispersed two-photon absorption in the near-infrared region. It is demonstrated that molecular structures with multi-branched π frameworks incorporating properly functionalized quinoxalinoid units would possess large molecular nonlinear absorptivities within the studied spectral range. Effective optical-power attenuation and stabilization behaviors in the nanosecond time domain of a selected representative dye molecule (i.e., compound 2) from this model compound set were also investigated and the results indicate that such structural motif could be a useful approach for the molecular design toward strong two-photon-absorbing material systems for quick-responsive and broadband optical-suppressing-related applications, particularly to confront long laser pulses.

Synthesis and characterization of a highly two-photon active dendrimer derived from 2,3,8-trifunctionalized indenoquinoxaline units

A dendritic chromophore derived from 2,3,8-trifunctionalized indenoquinoxaline units was synthesized and experimentally shown to manifest very strong and widely-dispersed two-photon absorption (2PA) across the dynamic tuning range of a Ti:sapphire laser. The maximum 2PA of the studied chromophore was found to reach ≈31u2006700 GM, indicating that 2,3,8-trifuctionalized indenoquinoxaline units are useful building moieties for the construction of highly active 2PA-dyes. In addition, this dendritic structure was also demonstrated to effectively regulate the optical power of femtosecond laser pulses at 800 nm.

Synthesis and Characterization of Two-Photon Active Chromophores Based on Tetrathienoacene (TTA) and Dithienothiophene (DTT)

Three new donor-π-donor (D-π-D) tetrathienoacene (thieno[2,3:4,5]thieno[3,2-b]thieno[2,3-d]thiophene (TTA))-cored chromophores, end-functionalized with electron-donating triphenylamine (TPA) groups, were developed and characterized for their two-photon-related properties by using both nano- and femtosecond laser pulses as the probing tools. TTA-based chromophores exhibit stronger and more widely dispersed two-photon absorption (2PA) than those of dithienothiophene (DTT)-based congeners. As a consequence, the bithiophene-conjugated TTA chromophore exhibits the highest maximum 2PA cross-section value (up to 2500u2005GM) with good thermal stability, and thus, it is the best performing two-photon chromophore among the studied model compounds. The bithiophene-conjugated DTT analogue exhibits the second highest maximum two-photon absorptivity of 1950u2005GM, which is nearly 7 times larger than that of previously reported DTT-based chromophores.

Synthesis and two-photon properties of a novel multi-branched chromophore with an unsymmetrically substituted scaffold derived from functionalized quinoxalinoid heterocycles

A star-shaped multi-polar chromophore (1) combining functionalized indenoquinoxaline and pyridopyrazine units has been synthesized and characterized for its two-photon absorption (2PA) properties both in the femtosecond and nanosecond time domains. Under our experimental conditions, this model fluorophore is found to manifest strong and widely dispersed two-photon absorption as well as effective power-limiting/stabilization properties against long laser pulses in the near-IR region.

Degenerate Two-Photon Absorption and Effective Optical-Power-Limiting Properties of Multipolar Chromophores Derived from 2,3,8-Trisubstituted Indenoquinoxaline

Two analogous multipolar chromophores (1 and 2) that contained 2,3,8-trisubstituted indenoquinoxaline moieties have been synthesized and characterized for their two-photon absorption properties, both in the femtosecond and nanosecond time regimes. We demonstrated that their multi-branched framework structures, which incorporated appropriately functionalized indenoquinoxaline units, afforded large molecular nonlinear absorptivities within the studied spectroscopic range. Effective optical-power-limiting and stabilization behaviors in the nanosecond regime of dye molecule (2) were also investigated and the results indicated that such a structural motif could be a useful approach to the molecular design of highly active two-photon systems for quick-response and related broadband optical-suppressing applications, in particular for confronting laser pulses of a long duration.

Synthesis and characterization of two-photon chromophores based on a tetrasubstituted tetraethynylethylene scaffold.

A new series of model dye molecules composed of three multibranched analogues based on the tetrasubstituted tetraethynylethylene structural motif have been synthesized and experimentally shown to possess strong and widely dispersed two-photon absorption (2PA) in the near-IR region. It was found that the spectral position of the major 2PA band could be tuned by the electronic nature of the selected substitution units. The studied model fluorophores also exhibited fairly low photodegradation of their fluorescence intensity even under prolonged UV-light irradiation, which is beneficial for the development of fluorescence probes that are needed for long-term light exposure. Furthermore, representative chromophores were selected to demonstrate the power-control properties within the femtosecond and nanosecond time domains.

Two- and three-photon absorption properties of fan-shaped dendrons derived from 2,3,8-trifunctionalized indenoquinoxaline units: synthesis and characterization

A model compound set that contains a series of fan-shaped chromophores using 2,3,8-trifunctionalized indenoquinoxaline units as the major building block of their π-framework was synthesized and characterized for their two- and three-photon absorption properties in the femtosecond regime based on two-photon-excited fluorescence and Z-scan techniques. The experimental results show that these dendritic fluorophores manifest strong and wide-dispersed two- and three-photon absorption bands within the near-infrared region, which indicates that 2,3,8-trifunctionalized indenoquinoxaline units are favorable building moieties for the construction of highly active multi-photon dyes. The maximum values of two- and three-photon absorption cross-sections for the largest dendron (i.e. compound D4) are ≈24u2006800 GM and 6 × 10−78 cm6 s2, respectively. A nearly linear ascending relationship between π-structural expansion and nonlinear absorption is observed for these compounds, implying that the currently utilized structural arrangement does not exert deleterious or cooperative effects on the multi-photon absorption properties of this model system. In addition, a representative dendritic structure is selected to demonstrate efficient optical power-limiting against femtosecond laser pulses at 790 nm.

trans/cis‐Isomerization of Fluorene‐Bridged Azo Chromophore with Significant Two‐Photon Absorbability at Near‐Infrared Wavelength

Azo-containing materials have been proven to possess second-order nonlinear optical (NLO) properties, but their third-order NLO properties, which involves two-photon absorption (2PA), has rarely been reported. In this study, we demonstrate a significant 2PA behavior of the novel azo chromophore incorporated with bilateral diphenylaminofluorenes (DPAFs) as a π framework. The electron-donating DPAF moieties cause a redshifted π-π* absorption band centered at 470 nm, thus allowing efficient blue-light-induced trans-to-cis photoisomerization with a rate constant of 2.04 × 10(-1) min(-1) at the photostationary state (PSS). The open-aperture Z-scan technique that adopted a femtosecond (fs) pulse laser as excitation source shows an appreciably higher 2PA cross-section for the fluorene-derived azo chromophore than that for common azobenzene dyes at near-infrared wavelength (λex =800 nm). Furthermore, the fs 2PA response is quite uniform regardless of the molecular geometry. On the basis of the computational modeling, the intramolecular charge-transfer (ICT) process from peripheral diphenylamines to the central azo group through a fluorene π bridge is crucial to this remarkable 2PA behavior.

Synthesis and two-photon properties of small dendritic chromophores containing functionalized quinoxalinoid heterocycles

Three dendritic chromophores containing functionalized quinoxalinoid units has been synthesized and experimentally shown to possess strong two-photon absorption in the near-IR region and could be promising candidates for optical-power-limiters against laser pulses with long duration.