Genmiao Wang

Record Multiphoton Absorption Cross-Sections by Dendrimer Organometalation

Large increases in molecular two-photon absorption, the onset of measurable molecular three-photon absorption, and record molecular four-photon absorption in organic π-delocalizable frameworks are achieved by incorporation of bis(diphosphine)ruthenium units with alkynyl linkages. The resultant ruthenium alkynyl-containing dendrimers exhibit strong multiphoton absorption activity through the biological and telecommunications windows in the near-infrared region. The ligated ruthenium units significantly enhance solubility and introduce fully reversible redox switchability to the optical properties. Increasing the ruthenium content leads to substantial increases in multiphoton absorption properties without any loss of optical transparency. This significant improvement in multiphoton absorption performance by incorporation of the organometallic units into the organic π-framework is maintained when the relevant parameters are scaled by molecular weights or number of delocalizable π-electrons. The four-photon absorption cross-section of the most metal-rich dendrimer is an order of magnitude greater than the previous record value.

Organometallic Complexes for Non-Linear Optics. 59. Syntheses and Optical Properties of Some Octupolar (N-Heterocyclic Carbene)gold Complexes

The syntheses of octupolar alkynes 1,3,5-{4-(4-HC≡CC6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (4) and 1,3,5-{4-(4-HC≡CC6H4-1-C≡C-4-C6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (6), diphenylamino-substituted 1,3,5-(4-Ph2NC6H4-1-C≡C)3C6H3 (7), 1,3,5-(4-Ph2NC6H4-1-C≡C-4-C6H4-1-C≡C)3C6H3 (8), 1,3,5-{4-(4-Ph2NC6H4-1-C≡C-4-C6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (9), and 1,3,5-{4-(4-Ph2NC6H4-1-C≡C-4-C6H4-1-C≡C-4-C6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (10), and (N-heterocyclic carbene)gold-appended 1,3,5-{[(NHC-iPr)Au]C≡C}3C6H3 (11), 1,3,5-{[(NHC-iPr)Au]C≡C-4-C6H4-1-C≡C}3C6H3 (12), 1,3,5-{4-([(NHC-iPr)Au]C≡C-4-C6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (13), and 1,3,5-{4-([(NHC-iPr)Au]C≡C-4-C6H4-1-C≡C-4-C6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (14) [NHC-iPru2009=u2009κC-cyclo-CN(2,6-C6H3iPr2)CH=CHN(2,6-C6H3iPr2)] are reported. The low-energy bands in the linear optical absorption spectra of all three sets of compounds are red-shifted and increase in intensity upon π-delocalizable ‘arm’ lengthening. The diphenylamino- and (NHC-iPr)gold-terminated compounds do not exhibit measurable second-harmonic generation as assessed by hyper-Rayleigh scattering at 1064u2009nm using nanosecond pulses. Computational studies have been employed to rationalize the optical properties of the new compounds. Calculations on 7–10 reveal that the lowest-energy transitions with large oscillator strengths are predominantly [Ph2NC6H4] (π) → [armsu2009+u2009core] (π*) in character, whereas calculations on 11–14 suggest that the low-energy transitions relate to the transfer of electron density from the Au-alkynyl core group to the terminal NHC groups.

Photovoltaic Effect of a Ferroelectric-Luminescent Heterostructure under Infrared Light Illumination

In this report, a ferroelectric-luminescent heterostructure is designed to convert infrared light into electric power. We use BiFeO3 (BFO) as the ferroelectric layer and Y2O3:Yb,Tm (YOT) as the upconversion layer. Different from conventional ferroelectric materials, this heterostructure exhibits switchable and stable photovoltaic effects under 980 nm illumination, whose energy is much lower than the band gap of BFO. The energy transfer mechanism in this heterostructure is therefore studied carefully. It is found that a highly efficient nonradiative energy transfer process from YOT to BFO plays a critical role in achieving the below-band-gap photon-excited photovoltaic effects in this heterostructure. Our results also indicate that by introducing asymmetric electrodes, both the photovoltage and photocurrent are further enhanced when the built-in field and the depolarization field are aligned. The construction of ferroelectric-luminescent heterostructure is consequently proposed as a promising route to enhance the photovoltaic effects of ferroelectric materials by extending the absorption of the solar spectrum.