A set of symmetrically substituted multibranched chromophores composed of three quinoxaline‐based congeners has been synthesized and experimentally shown to possess strong and widely dispersed two‐photon absorptivities in the visible to near‐IR region under the irradiation of femtosecond and nanosecond laser pulses. The electronic properties of the central π bridges incorporated into the final structures are closely connected to the molecular two‐photon activities of these model compounds. Effective optical‐power attenuation and stabilization behaviors in the nanosecond time domain of these dye molecules were also investigated. The structural motif of these compounds provides a useful approach for the molecular design of strong two‐photon absorbing material systems with the potential for quick‐responsive and broadband optical‐control related applications, particularly for long‐duration laser pulses in the near‐IR region.
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.
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 multipolar fluorophores using ladder‐type oligo‐(p‐phenylene) units as the central π‐bridges and functionalized diquinoxalinylamino moieties as the peripheral groups have been synthesized and experimentally shown to manifest strong two‐photon absorption (2PA) and medium‐high up‐converted emission properties in the near‐IR (NIR) spectral region under the irradiation of femtosecond laser pulses. Tentative analysis of the structure–2PA property revealed that in the presented structural combination, diquinoxalinylamino units are useful 2PA‐enhancing subunits when properly incorporated. The π‐conjugation length of the central oligo‐(p‐phenylene) components was also found to be one of the key parameters that relates to the magnitude of the overall molecular 2PA properties in the studied molecular system, and this structural motif provides access to highly efficient two‐photon absorbers with large two‐photon action cross‐section values.
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