Synthesis and nonlinear optical properties in the near-IR range of stilbazolium dyes

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation

“…Several other examples based on pyridinium-based compounds ( 101a – c , 102 , Chart ) were prepared and characterized for OL. Compounds 101 and 102 presented TPA stronger in the NIR than in the visible range. , It was realized that the length of the alkyl chain played an important role in enhancing the TPA cross section through chain length increase …”

“…Compounds 101 and 102 presented TPA stronger in the NIR than in the visible range. 751,752 It was realized that the length of the alkyl chain played an important role in enhancing the TPA cross section through chain length increase. 751 Three-photon absorption was observed in compounds 103− 107 (Chart 26).…”

“…751,752 It was realized that the length of the alkyl chain played an important role in enhancing the TPA cross section through chain length increase. 751 Three-photon absorption was observed in compounds 103− 107 (Chart 26). 753 Using a mode-locked/Q-switched Nd:YAG pulse with a duration of 35 ps and a repetition rate of 10 Hz at 1064 nm, the molecular three-photon absorption cross sections of 103−107 resulted in the order 10 −78 −10 −76 cm 6 s 2 .…”

Enhancement of Two-Photon Absorption Parallels Intramolecular Charge-Transfer Efficiency in Quadrupolar versus Dipolar Cationic Chromophores

“…35−37 In terms of electron donors, dialkylamino substituents have shown higher NLO responses when employed in molecular structures to replace the well-known and widely used dimethylamino group. 38,39 In fact, the TPA cross sections are enhanced by lengthening of the alkyl chain. Moreover, both the ICT and the optical nonlinearity have been found to improve in elongated and more conjugated push−pull polyenes with π-linkers of increasing length.…”

“…Several efficient strategies have been put forward to develop conjugated molecules with improved NLO responses, including dipolar-type molecules with a donor–bridge–acceptor (D−π–A) motif and quadrupolar-type molecules with a D−π–A−π–D structure, where the latter have been highlighted for their excellent properties. − Indeed, symmetrical quadrupolar compounds have been found experimentally and theoretically to demonstrate enhanced TPA with respect to the dipolar analogues. ,− The observed TPA cross sections of dipolar and quadrupolar structures are in accordance with the fact that the donor−π–acceptor molecules with increased dimensionality exhibit improved NLO and TPA properties. TPA enhancement for the quadrupolar compounds is attributed to more effective electronic delocalization. − , A deep understanding of the solvatochromic and TPA properties of such quadrupolar chromophores − has been often reached by invoking the occurrence of symmetry-breaking phenomena. ,,− Several works have unambiguously shown that TPA is strongly influenced by the photoinduced intramolecular charge transfer occurring in these systems containing electron-donor and electron-acceptor groups. , Cationic chromophores (such as methylpyridinium and methylquinolinium) have proven to be promising as electron-deficient moieties, not only for their significant electron-withdrawing ability but also for their water solubility, which is very appealing for possible biological and medical applications. − In terms of electron donors, dialkylamino substituents have shown higher NLO responses when employed in molecular structures to replace the well-known and widely used dimethylamino group. , In fact, the TPA cross sections are enhanced by lengthening of the alkyl chain. Moreover, both the ICT and the optical nonlinearity have been found to improve in elongated and more conjugated push–pull polyenes with π-linkers of increasing length. − …”