A series of new donor–p-acceptor type compounds with trivalent boron as acceptor which show strong two-photon excited up-conversion fluorescence have been synthesized and one crystal structure described.

The synthesis, structure, and fluorescence properties of a series of new donor -π- acceptor (D-π-A) type compounds, with a trivalent boron, protected by two mesityl groups, as acceptor, and with various typical donors and different-conjugated bridges, are reported. All these stable organoboron compounds show intense singlephoton excited fluorescence (SPEF) and two-photon excited fluorescence (TPEF) in a wide spectral range from blue to green, with the spectral peak position of the SPEF being basically the same as that of the TPEF. The remarkably strong C B(mesityl)2 bonding, and the well-conjugated -system, shown in X-ray crystal structures of two compounds, indicate some charge transfer features of the ground state. Meanwhile, spectral data indicate that the charge transfer from donor to acceptor is greatly enhanced in the excited states. Based on typical structural data and comprehensive spectral data, the following structure-property relationships can be drawn: 1) the moderate arylamino donor can more effectively enhance the SPEF and TPEF intensities than can the strong alkylamino donor; 2) stilbene is a better-bridge than styrylthiophene for its capability of enhancing and blueshifting the SPEF and TPEF of the corresponding D-π-A compounds; and 3) when compared to its boron-free precursors and other analogues, -B(mesityl) 2 invariably and consistently acts as an effective SPEF and TPEF fluorophore in all this series of organoboron compounds, which may result from its strong-electron-withdrawing and charge transfer-inducing nature in the ground-state and, more dominantly, in the excited-state. Combining all the above positive structure factors, trans-4-N,N-diphenylamino-4-dimesitylborylstilbene (compound 3) stands out as the optimized green SPEF and TPEF emitter. This compound exhibits an SPEF quantum yield of 0.91 at 522 nm in THF, a TPEF cross-section that is an order of magnitude larger than that of its boron-free precursor upon excitation by 800nm femto-second laser pulses, and a two-photon absorption section of 3.0 10 48 cm4 s. In the blue light region, trans-4 -N-carbazolyl-4-dimesitylborylstilbene (compound 4) shows significant SPEF and TPEF properties, with 0.79 at 464 nm in THF and a large value, which is five times that of fluorescein upon excitation by 740 nm femto-second laser pulses.

We have synthesized a series of new D−π−A compounds that feature various electron donors and a fixed benzothiazolyl unit as an electron acceptor. The crystal structure of compound 3 [trans,trans-2-{4-[(4-N-carbazolyl)styryl]styryl}-1,3-benzothiazole, CSSB] was determined. All these compounds show high fluorescence quantum yields and 3 in toluene gives the most intense blue emission around 450 nm with a quantum yield of Φ = 0.69. When excited at 800 nm by a Ti: sapphire femtosecond laser, these compounds exhibit strong two-photon-excited fluorescence (TPEF) in the blue-to-orange region. The measured TPEF cross-section of compound 2 [trans,trans-2-{4-[4-(N,N-diphenylamino)styryl]- styryl}-1,3-benzothiazole, DPSSB], for example, is about 6.1 times that of Coumarin 307. hotophysical data indicate that these compounds are polar in the ground state and have an enhanced polarity in the excited state, and that the electron donating ability of a dialkylamino group is much stronger than that of a diarylamino group.

A new molecular conductor PyH[Pd(dmit)2]2 (PyH=pyridinium, dmit=2-thioxo-1,3-dithiole-4,5-dithiolato) has been synthesized and structurally investigated. The room temperature conductivity at a certain direction on (001) plane was measured to be as high as a 2

Several donor-p-donor (D-p-D), acceptor-p-acceptor (A-p-A), and donor-p-acceptor (D-p-A) types of organic compounds with fluorene as p bridge and dimesitylboryl group as electron acceptor, which show strong two-photon excited blue fluorescence, have been synthesized and structurally investigated. The symmetric A-p-A type of compound exhibits the shortest wavelength of twophoton excited fluorescence (TPEF) at λem=405 nm under the excitation of λex=730nm; the unsymmetric D-p-A type of compound with diphenylamino as donor exhibits the most intense TPEF at blue region (λem=484 nm) with a two-photon absorption cross-section of 425GM under λex=800nm.