Two series of related donor–acceptor conjugated dipolar, pseudo‐quadrupolar (V‐shaped) and octupolar molecular systems based on the p‐dimesitylborylphenylethynylaniline core, namely, 4‐(4‐dimesitylborylphenylethynyl)‐N,N‐dimethylaniline, 4‐[4‐(4‐dimesitylborylphenylethynyl)phenylethynyl]‐N,N‐dimethylaniline, 3,6‐bis(4‐dimesitylborylphenylethynyl)‐N‐n‐butylcarbazole and tris[4‐(4‐dimesitylborylphenylethynyl)phenyl]amine, and on the E‐p‐dimesitylborylethenylaniline motif, namely, E‐4‐dimesitylborylethenyl‐N,N‐di(4‐tolyl)aniline, 3,6‐bis(E‐dimesitylborylethenyl)‐N‐n‐butylcarbazole and tris(E‐4‐dimesitylborylethenylphenyl)amine have been synthesised by palladium‐catalyzed cross‐coupling and hydroboration routes, respectively. Their absorption and emission maxima, fluorescence lifetimes and quantum yields have been obtained and their two‐photon absorption (TPA) spectra and TPA cross‐sections have been examined. Of these systems, the octupolar compound tris(E‐4‐dimesitylborylethenylphenyl)amine has been shown to exhibit the largest TPA cross‐section among the two series of approximately 1000 GM at 740 nm. Its TPA performance is comparable to those of other triphenylamine‐based octupoles of similar size. The combination of such large TPA cross‐sections and high emission quantum yields, up to 0.94, make these systems attractive for applications involving two‐photon excited fluorescence (TPEF).

New fluorophores, combining broad, very high two-photon absorption in the near-infrared region with a marked dependence of their emission spectra on solvent polarity, have been designed as model probes for two-photon sensing of the chemical environment.

Investigations of the non-linear optical properties of a novel series of A–π–A quadrupoles, based on dimesitylboron end-groups, reveal the promising potential of elongated vinylboranes derivatives for combined enhanced two-photon absorption cross-section and improved transparency in the visible region. In addition, the excited state lifetime can be significantly enhanced in A–π–A′–π–A derivatives. This opens a new route towards optimized molecules for optical power limiting.

Nanoscopic fluorescent dendrimers having up to 96 two-photon chromophores and showing very large two-photon absorption cross-sections (up to 56 000 GM) were designed as a complementary “organic” alternative to quantum dots.

Evolution of the static HRS hyperpolarizability of a tricyanopropylidene-based merocyanine dye with the length of the polyenic bridge, as calculated using various ab initio and DFT approximations.