Feipeng Chen

Design and synthesis of solution processable small molecules towards high photovoltaic performance

We successfully synthesized a series of novel symmetrical solution processable small molecules (APPM, AAPM and ATPM) consisting of the electron-accepting moiety (2-pyran-4-ylidenemalononitrile) (PM) and the electron-donating moiety (triphenylamine) linked by different electron-donating moieties (phenothiazine, triphenylamine and thiophene) through a Suzuki coupling reaction. Differential scanning calorimetry (DSC) measurement indicates that APPM and AAPM shows relatively high glass-transition temperature of ca. 137 °C and 163 °C, while the melting point of ATPM is at ca. 164 °C. UV-vis absorption spectra show that the combination of the PM moiety with moieties with a gradually increased electron-donating ability results in an enhanced intramolecular charge transfer (ICT) transition, which leads to an extension of the absorption spectral range and a reduction of the band gap of the molecules. Both cyclic voltammetry measurement and theoretical calculations displayed that the highest occupied molecular orbital (HOMO) energy levels of the molecules could be fine-tuned by changing the electron-donating ability of the electron-donating moieties. The bulk heterojunction (BHJ) photovoltaic devices with a structure of ITO/PEDOT/PSS/small molecules/PCBM/LiF/Al were fabricated by using the small molecules as donors and (6,6)-phenyl C61-butyric acid methyl ester (PCBM) as acceptor. Power conversion efficiencies (PCE) of 0.65%, 0.94% and 1.31% were achieved for the photovoltaic devices based on APPM/PCBM, AAPM/PCBM and ATPM/PCBM under simulated AM 1.5 illumination (100 mW cm−2), respectively. The open circuit voltage of 1.0 V obtained from the device based on ATPM/PCBM is one of the highest values for organic solar cells based on solution processable small molecules.

Aggregation emission properties and self-assembly of conjugated oligocarbazoles.

Conjugated oligocarbazoles with a 9,10-divinylanthracene core have been synthesized, and exhibit the transition from aggregation-induced emission (AIE) to aggregation-induced emission enhancement (AIEE) behaviour with extending conjugation length; self-assembly of the Cz4 molecule affords nanorings with high fluorescent efficiency.

Solid state emission enhancement of 9,10-distyrylanthracene derivatives and amplified spontaneous emission from a large single crystal

Methyl-substituted 9,10-distyrylanthracene was synthesized by a simple Heck reaction and its photophysical properties investigated. Tight intermolecular stacking through supramolecular interactions in the crystal not only induced strong fluorescence emission with a high fluorescence efficiency of 35% but also conducted the formation of large size and high quality needle-like single crystals. Amplified spontaneous emission (ASE) with a low threshold value of 10 μJ pulse−1 was observed.

Synthesis, characterization, two-photon absorption, and optical limiting properties of triphenylamine-based dendrimers

Three π-conjugated dendrimers (Ph-G0, Ph-G1 and Ph-G2) bearing triphenylamine moieties have been synthesized through a convergent synthetic strategy without any protection–deprotection chemistry. The linear photophysical properties, two-photon absorption (TPA), and optical limiting behavior of the dendrimers were investigated in solution at room temperature. Linear absorption and emission spectra revealed a bathochromic shift and decreased fluorescence quantum yields with increasing dendrimer generation. A strong cooperative effect in the TPA absorption of these dendrimers was observed. The TPA cross-sections increase gradually with the proportion of triphenylamine units and the maximum value of the TPA cross-section can reach 5690 GM for Ph-G2. These triphenylamine-based dendrimers exhibited efficient two-photon optical limiting under femtosecond excitation.

Two-photon induced amplified spontaneous emission from needlelike triphenylamine-containing derivative crystals with low threshold

Two-photon induced amplified spontaneous emission (ASE) characteristics of a needlelike crystal were studied. Under two-photon excitation, the upconverted light emission was confined within the crystal and self-waveguided along the needle axis then radiated from the needle tips. The full width at half maximum of the two-photon excited fluorescence reaches 6.5 nm and ASE threshold is as low as 0.29 mJ pulse−1 cm−2 for the N-(4-(4-(4-(diphenylamino)styryl)styryl)phenyl)-N-phenylbenzene amine crystal, comparable with those achieved by single-photon pumping. The needlelike crystal is shown to be a promising candidate for frequency up-converted organic semiconductor microlasers.

Two-Photon Absorption and Spectral-Narrowed Light Source

This paper reports the two-photon absorption (TPA) and the spectral-narrowed light emission (SNLE) from the crystals of 9, 10-distyrylanthracene (DSA) derivatives. The results obtained by the Z-scan method show that the tested molecules possess high TPA cross sections. Upon near-IR excitation, strong two-photon-excited fluorescence could be observed in the crystals of four types of materials. Furthermore, SNLE with low threshold occurs in three of the four crystals under pumping with the second harmonic generated in the amplifier. Single crystals of the DSA derivatives exhibit unique photonic properties, including strong solid-state fluorescence, large TPA cross section, and stimulated emission. The results demonstrate that these are potential candidates for compact and practical solid-state laser applications.