Luminogenic molecules [(TPE)₃ (1), TPE-C = C-TPE-C = C-TPE (2), and TPE-C≡C-TPE-C≡C-TPE (3)] and their polymers P1–P3 are constructed from tetraphenylethene (TPE) building blocks in high yields by Suzuki, Witting, and Sonogashira coupling reactions. All the compounds are soluble and enjoy high thermal stability, losing little of their weights when they are heated to 290–528 °C under nitrogen or 288–436 °C in air. Analyses by UV spectroscopy and cyclic voltammetry as well as theoretical calculations show that the conjugation of the luminophores is in the order of 2 > 3 > 1, P2 > P3 > P1, and P1–P3 > 1–3. All the molecules and polymers are weakly emissive in solutions. They, however, become strong emitters in the aggregate state with fluorescence quantum yields up to 90%. Both 1–3 and P1–P3 exhibit the feature of aggregation-enhanced two-photon excited fluorescence. Large two-photon absorption cross sections (up to ∼900 GM) are observed in the nanoaggregates of the polymers. Thin solid films of the polymers show high refractive indices (RI = 1.7649 − 1.6873) in a wide wavelength region of 400–1700 nm, high modified Abbé numbers (v_D′ up to 3436), and low optical dispersions (D′ down to 2.9 × 10⁻⁴). The light emissions of the polymers can be quenched exponentially by picric acid with large quenching constants, suggesting that they can be utilized as efficient chemosensors for explosive detection.

In this work the two-photon activity of nanoparticles obtained from a fluorene monomer (M1) and its cross-conjugated polymer (P1) is reported. Aqueous suspensions of M1 and P1 nanoparticles prepared through the reprecipitation method exhibited maximum two-photon absorption (TPA) cross-sections of 84 and 9860 GM (1 GM = 10⁻⁵⁰ cm⁴ s) at 740 nm, respectively, and a fluorescence quantum yield of ∼1. Such a two-photon activity was practically equal with respect to that for molecular solutions of M1 and P1. These materials were then successfully encapsulated into silica nanoparticles to provide bio-compatibly. A lung cancer cell line (A549) and a human cervical cancer cell line (HeLa cells) were incubated with our fluorescent silica nanoparticles to carry out two-photon imaging. By means of these studies we demonstrate that optimized nonlinear optical polymers loaded in silica nanoparticles can be used as efficient probes with low cytotoxicity and good photostability for two-photon fluorescence microscopy. To the best of our knowledge, studies concerning polymer-doped silica nanoparticles exhibiting large two-photon activity have not been reported in the literature.

A series of sixteen new 2-julolidin-imidazo[1,2-a]pyridine bound-type bis-heterocycles were synthesized in good to excellent yields (61–98%) via an MW-assisted Groebke–Blackburn–Bienaymé (GBB) reaction. Then, experimental studies were conducted to determine the luminescence properties of these compounds. Various high quantum yields were found. In fact, one product exhibited a quantum yield (86.6%) comparable to that of the reference compound rhodamine (94.8%). Finally, further computational studies were performed by means of TD-DFT to calculate their HOMO–LUMO distributions and theoretical absorption spectra. A good agreement between the experimental and computational results was obtained, which provides a rationalized explanation for the observed structure/property relationships.