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A solution processible organic conjugated molecule 2-[2,6-bis-(2-{4-[2-(4-diphenylaminophenyl)vinyl]phenyl}vinyl)pyran-4-ylidene]malononitrile (TPA−DCM−TPA) was designed and synthesized for application in organic solar cells (OSCs). The molecule consists of two electron-rich triphenylamine moieties and one electron-deficient 2-pyran-4-ylidenemalononitrile unit linked with conjugated bridges. The optical and electrochemical properties, the light-induced electron spin resonance (LESR), and the electronic ground state configuration of the compound were characterized. TPA−DCM−TPA film showed a broad absorption band covering from 350 to 650 nm. The bulk-heterojunction OSCs with the device structure of ITO/PEDOT:PSS/TPA−DCM−TPA:PCBM/LiF/Al or Ba/Al were fabricated, in which TPA−DCM−TPA was used as donor and PCBM as acceptor material. The open-circuit voltage, short-circuit current, and power-conversion efficiency of the optimized OSC with Ba/Al as cathode, TPA−DCM−TPA:PCBM = 1:3 (w/w), and ca. 85 nm thickness of the active layer reached 0.9 V, 2.14 mA/cm2, and 0.79%, respectively, under the illumination of AM1.5, 100 mW/cm2. The results indicate that TPA−DCM−TPA is a promising photovoltaic organic molecule.

The photophysical properties of two newly synthesized photoactive compounds with asymmetrical D-π-A structure and symmetrical D-π-A-π-D structure are investigated in different aprotic solvents by steady-state and femtosecond fluorescence depletion measurements. It is found that the asymmetrical DA compound has larger dipole moment change than that of the symmetrical DAD compound upon excitation, where the dipole moments of the two compounds have been estimated using the Lippert-Mataga equation. Furthermore, the steady-state spectral results show that increasing solvent polarity results in small solvatochromic shift in the absorption maxima but a large red shift in the fluorescence maxima for them, indicating that the dipole moment changes mainly reflect the changes of dipole moment in excited-state rather than in ground state. The redshifted fluorescence band is attributed to an intramolecular charge transfer (ICT) state upon photoexcitation, which could result in a strong interaction with the surrounding solvents to cause the fast solvent reorganization. The resulting ICT states of symmetrical compounds are less polar than the asymmetrical compounds, indicating the different extents of stabilization of solute-solvent interaction in the excited state. Femtosecond fluorescence depletion measurements are further employed to investigate the fast solvation effects and dynamics of the ICT state of these two novel compounds. The femtosecond fluorescence depletion results show that the DA compound has faster solvation time than that of DAD compound, which corresponds to the formation of relaxed ICT state (i.e., a final ICT state with rearranged solvent molecules after solvation) in polar solvents. It is therefore reasonably understood that the ICT compounds with asymmetrical (D-π-A) structure have better performance for those photovoltaic devices, which strongly rely on the nature of the electron pushpull ability, compared to those symmetrical compounds (D-π-A-π-D).

In order to better understand the nature of intramolecular charge and energy transfer in multibranched molecules, we have synthesized and studied the photophysical properties of a monomer quadrupolar chromophore with donor−acceptor−donor (D−A−D) electronic push−pull structure, together with its V-shaped dimer and star-shaped trimers. The comparison of steady-state absorption spectra and fluorescence excitation anisotropy spectra of these chromophores show evidence of weak interaction (such as charge and energy transfer) among the branches. Moreover, similar fluorescence and solvation behavior of monomer and branched chromophores (dimer and trimer) implies that the interaction among the branches is not strong enough to make a significant distinction between these molecules, due to the weak interaction and intrinsic structural disorder in branched molecules. Furthermore, the interaction between the branches can be enhanced by inserting π bridge spacers (−CC− or −CC−) between the core donor and the acceptor. This improvement leads to a remarkable enhancement of two-photon cross-sections, indicating that the interbranch interaction results in the amplification of transition dipole moments between ground states and excited states. The interpretations of the observed photophysical properties are further supported by theoretical investigation, which reveal that the changes of the transition dipole moments of the branched quadrupolar chromophores play a critical role in observed the two-photon absorption (2PA) cross-section for an intramolecular charge transfer (ICT) state interaction in the multibranched quadrupolar chromophores.

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Strong intermolecular interactions usually result in decreases in solubility and fluorescence efficiency of organic molecules. Therefore, amorphous materials are highly pursued when designing solution‐processable, electroluminescent organic molecules. In this paper, a non‐planar binaphthyl moiety is presented as a way of reducing intermolecular interactions and four binaphthyl‐containing molecules (BNCMs): green‐emitting BBB and TBT as well as red‐emitting BTBTB and TBBBT, are designed and synthesized. The photophysical and electrochemical properties of the molecules are systematically investigated and it is found that TBT, TBBBT, and BTBTB solutions show high photoluminescence (PL) quantum efficiencies of 0.41, 0.54, and 0.48, respectively. Based on the good solubility and amorphous film‐forming ability of the synthesized BNCMs, double‐layer structured organic light‐emitting diodes (OLEDs) with BNCMs as emitting layer and poly(N‐vinylcarbazole) (PVK) or a blend of poly[N,N′‐bis(4‐butylphenyl)‐N,N′‐bis(phenyl)benzidine] and PVK as hole‐transporting layer are fabricated by a simple solution spin‐coating procedure. Amongst those, the BTBTB based OLED, for example, reaches a high maximum luminance of 8315 cd · m−2 and a maximum luminous efficiency of 1.95 cd · A−1 at a low turn‐on voltage of 2.2 V. This is one of the best performances of a spin‐coated OLED reported so far. In addition, by doping the green and red BNCMs into a blue‐emitting host material poly(9,9‐dioctylfluorene‐2,7‐diyl) high performance white light‐emitting diodes with pure white light emission and a maximum luminance of 4000 cd · m−2 are realized.

Alternating and random copolymers of 2-vinylnaphthalene and methacrylic acid have been loaded with small amounts (0-4 mol %) of anthracene by direct esterification with 9-anthracenemethanol. Energy transfer from the singlet state of naphthalene to anthracene was studied in 77 K glasses and roomtemperature solutions. In all cases the quantum efficiency ( ) of energy transfer was higher for the anthryl-loaded alternating copolymer than for the random copolymer. On the basis of the steady-state value of and that derived from the naphthalene fluorescence decay, it is suggested that both the naphthalene and anthracene singlet states can be populated by a common precursor state in addition to sensitization of the anthracene singlet by energy transfer from the naphthalene singlet. It is proposed that reasonably efficient energy migration between naphthalene groups occurs at longer time, but ultimately excitation self-trapping may occur. For the alternating copolymer in room-temperature solution the fluorescence decay of the naphthalene in the presence of anthryl acceptors can be fit to a function of the form exp(-t/r0 -at") as is expected for a "fractal structure". On the basis of the deconvolution of the room-temperature fluorescence spectrum of the random copolymer into monomer, excimer, and anthracene components, it is proposed that at higher loading of anthracene the host polymer conformation is perturbed, leading to a decrease of excimer-forming sites.