Synthesis,Two‐Photon Absorption and Optical Limiting Properties of Multi‐branched Styryl Derivatives Based on 1,3,5‐Triazine

Five new multi‐branched two‐photon absorption triazine chromophores ( T1 – T5 ) with different donor strength, conjugation length, and direction of charge transfer have been designed and synthesized. The one‐photon fluorescence, fluorescence quantum yields, and two‐photon properties have been investigated. The two‐photon absorption (2PA) cross sections measured by the open aperture Z‐scan technique were determined to be 447, 854, 1023, 603, and 766 GM for T1 , T2 , T3 , T4 , and T5 , respectively. This result indicates that their 2PA cross section values (σ) increase with increasing electron‐donating strength of the end group, extending the conjugation length of the system, and introducing electron‐withdrawing perfluoroalkyl as side groups to the end donor. In addition, the σ value of T5 is also larger than that of T1 , which provides evidence that the σ value is relative to the direction of charge transfer (from the ends to the center of the molecule or from the center to the ends). Moreover, significant enhancement of the two‐photon absorption cross section was achieved by introducing a thiophene moiety to a conjugated CC bond. At the same time, the optical limiting behavior for these chromophores was studied by using a focused 800 nm laser beam with pulses of 140 fs duration. It was found that these molecules also exhibit good optical limiting properties. These initial results clearly demonstrate that multi‐branched triazine chromophores are a highly suitable class of two‐photon absorbing materials.     

Solution‐Processed Bulk‐Heterojunction Photovoltaic Cells Based on Dendritic and Star‐Shaped D‐π‐A Organic Dyes

A series of D ‐π‐A organic dendritic and star‐shaped molecules based on three various chromophores (i.e., the truxene nodes, triphenylamine moieties as the donor, and benzothiadiazole chromophore as the acceptor) and their corresponding model compounds are facilely developed. Their photophysical and electrochemical properties are investigated in detail by UV/Vis absorption and photoluminescent spectroscopy, and cyclic voltammetry. By changing the various conjugated spacers (i.e., single bond, double bond, and triple bond) among the three chromophores of dendritic series, their photophysical properties (that is, the one‐photon absorption range and two‐photon absorption cross‐section values) are effectively modulated. All D ‐π‐A conjugated oligomers show a broad and strong absorption band from 250 to 700 nm in thin films. Solution‐processed bulk‐heterojunction photovoltaic devices using our oligomer as donor and PCBM as acceptor are fabricated and measured. The power conversion efficiency of the devices based on our oligomers continuously increases from DBTTr to TRTD2A as a result of an increasing relative absorption intensity in longer wavelength region by changing the donor‐acceptor ratio and conjugated spacers between the donor and acceptor. The power conversion efficiency of the devices based on TRTD2A was 0.54 % under the illumination of AM 1.5 and 100 mW cm^?2, which is the highest value recorded based on D ‐π‐A conjugated oligomers containing triphenylamine moieties and benzothiadiazole chromophores with truxene to date.     

Synthesis,Photophysical Properties of Tribranched Chromophores Based on 1,3,5‐Triazine Core and Different Electro‐donating End‐groups

Three two‐photon absorption (TPA) tribranched chromophores were successfully prepared, in which 1,3,5‐triazine is been as electron deficient core, 1,4‐phenylenedivinylene as conjugated bridge, 3,4‐ethylenedioxythiophene (EDOT) ( T1 ), N‐methylpyrrole ( T2 ) or triphenylamine ( T3 ) as electron‐donating end‐groups. Their photophysical properties were studied by absorption, one‐ and two‐photon fluorescence and TPA cross‐section determination. The nonlinear transmission (NLT) measurement in femtoseconds (fs) regime at 800 nm indicates that TPA cross‐section (₂ values of T1 , T2 and T3 with extended Π‐conjugated bridge are much larger than the corresponding chromophore T4 with a short length bridge, and TPA cross‐section of T1 with end‐groups EDOT exhibits a remarkable enhancement compared with T2 and T3 having the same length Π‐system. The chromophores T1 , T2 and T3 show also remarkable up‐converted luminescence and optical limiting activity.     

Molecular design of nonlinear optical polymer based on DCM to enhance the NLO efficiency and thermal stability

This study synthesized and characterized a novel series of polyurethanes containing nonlinear optic (NLO) chromophores, which possess different dimensional or various isolation‐groups. These chromophores are based on 4‐(dicyanomethylene)‐2‐methyl‐6‐(p‐(dimethylamino)styryl)‐4H‐pyran (DCM‐typed dye). The NLO polyurethane containing a one‐dimensional isolation‐group of chromophores efficiently enhances thermal stability, but poling efficiency is not always improved as the size of isolation‐group increases. The enormous isolation group restrained the mobility of chromophore in the polymer matrix and shows a worsening SH intensity. The maximum second harmonic coefficient (d₃₃ = 68.7 pm/V) is displayed as benzene is attaching to chromophore moieties as isolation‐group in this study. Polyurethane containing two‐dimensional chromophore shows superior thermal stability due to the large volume required to rotate the chromophore in the polymer matrix. Two‐dimensional system exhibits lower SH intensity due to the rigid polymer main chain and twisted conjugated plane. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4937–4949, 2009     

Two‐Photon STED Spectral Determination for a New V‐Shaped Organic Fluorescent Probe with Efficient Two‐Photon Absorption

Two‐photon stimulated emission depletion (STED) cross sections were determined over a broad spectral range for a novel two‐photon absorbing organic molecule, representing the first such report. The synthesis, comprehensive linear photophysical, two‐photon absorption (2PA), and stimulated emission properties of a new fluorene‐based compound, (E)‐2‐{3‐[2‐(7‐(diphenylamino)‐9,9‐diethyl‐9H‐fluoren‐2‐yl)vinyl]‐5‐methyl‐4‐oxocyclohexa‐2,5‐dienylidene} malononitrile ( 1 ), are presented. Linear spectral parameters, including excitation anisotropy and fluorescence lifetimes, were obtained over a broad range of organic solvents at room temperature. The degenerate two‐photon absorption (2PA) spectrum of 1 was determined with a combination of the direct open‐aperture Z‐scan and relative two‐photon‐induced fluorescence methods using 1 kHz femtosecond excitation. The maximum value of the 2PA cross section ～1700 GM was observed in the main, long wavelength, one‐photon absorption band. One‐ and two‐photon stimulated emission spectra of 1 were obtained over a broad spectral range using a femtosecond pump–probe technique, resulting in relatively high two‐photon stimulated emission depletion cross sections (～1200 GM). A potential application of 1 in bioimaging was demonstrated through one‐ and two‐photon fluorescence microscopy images of HCT 116 cells incubated with micelle‐encapsulated dye.     

The impact of diperfluorophenyl and thienyl substituents on the electronic structures and charge transport properties of the fused thiophene semiconductors

The charge transport properties of 3 fused thiophene semiconductors, end-capped with diperfluorophenylthien-2-yl (DFPT) groups (DFPT-thieno[2′, 3′:4, 5]thieno[3, 2-b]thieno[2, 3-d]thiophene (TTA), DFPT-dithieno[2, 3-b:3′, 2′-d]thiophenes (DTT), and DFPT-thieno[3, 2-b]thiophene (TT)), are explored via density functional theory (DFT). To gain a better understanding of the impact of diperfluorophenyl and thienyl substituents on the electronic structures and charge transport properties of these molecules, the geometric structures, reorganization energy, frontier molecular orbitals, molecular ionization potentials and electron affinities, absorption spectra of the corresponding molecules including diperfluorophenyl (DFP)-TTA, DFP-DTT, DFP-TT, dithienyl (DT)-TTA, DT-DTT, DT-TT as well as their parent molecules (TTA, DTT and TT) are investigated for comparison. The calculated results show that introducing perfluorophenyl groups to the fused thiophenes could be a good strategy to promote electron transport, while the insertion of additional thiophene rings to DFP-end-capped derivatives could further extend the π-conjugation and enhance the charge transport properties of DFPT-end-capped analogs.     

Experimental and Theoretical Studies of Quadrupolar Oligothiophene‐Cored Chromophores Containing Dimesitylboryl Moieties as π‐Accepting End‐Groups: Syntheses,Structures, Fluorescence,and One‐ and Two‐Photon Absorption

Quadrupolar oligothiophene chromophores composed of four to five thiophene rings with two terminal (E)‐dimesitylborylvinyl groups ( 4 V – 5 V ), and five thiophene rings with two terminal aryldimesitylboryl groups ( 5 B ), as well as an analogue of 5 V with a central EDOT ring ( 5 VE ), have been synthesized via Pd‐catalyzed cross‐coupling reactions in high yields (66–89 %). Crystal structures of 4 V , 5 B , bithiophene 2 V , and five thiophene‐derived intermediates are reported. Chromophores 4 V , 5 V , 5 B and 5 VE have photoluminescence quantum yields of 0.26–0.29, which are higher than those of the shorter analogues 1 V – 3 V (0.01–0.20), and short fluorescence lifetimes (0.50–1.05 ns). Two‐photon absorption (TPA) spectra have been measured for 2 V – 5 V , 5 B and 5 VE in the range 750–920 nm. The measured TPA cross‐sections for the series 2 V – 5 V increase steadily with length up to a maximum of 1930 GM. We compare the TPA properties of 2 V – 5 V with the related compounds 5 B and 5 VE , giving insight into the structure–property relationship for this class of chromophore. DFT and TD‐DFT results, including calculated TPA spectra, complement the experimental findings and contribute to their interpretation. A comparison to other related thiophene and dimesitylboryl compounds indicates that our design strategy is promising for the synthesis of efficient dyes for two‐photon‐excited fluorescence applications.     

Synthesis,One‐ and Two‐Photon Photophysical and Excited‐State Properties,and Sensing Application of a New Phosphorescent Dinuclear Cationic Iridium(III) Complex

A new phosphorescent dinuclear cationic iridium(III) complex ( Ir1 ) with a donor–acceptor–π‐bridge–acceptor–donor (D? A? π? A? D)‐conjugated oligomer ( L1 ) as a N^N ligand and a triarylboron compound as a C^N ligand has been synthesized. The photophysical and excited‐state properties of Ir1 and L1 were investigated by UV/Vis absorption spectroscopy, photoluminescence spectroscopy, and molecular‐orbital calculations, and they were compared with those of the mononuclear iridium(III) complex [Ir(Bpq)₂(bpy)]⁺PF₆^? ( Ir0 ). Compared with Ir0 , complex Ir1 shows a more‐intense optical‐absorption capability, especially in the visible‐light region. For example, complex Ir1 shows an intense absorption band that is centered at λ=448 nm with a molar extinction coefficient (ε) of about 10⁴, which is rarely observed for iridium(III) complexes. Complex Ir1 displays highly efficient orange–red phosphorescent emission with an emission wavelength of 606 nm and a quantum efficiency of 0.13 at room temperature. We also investigated the two‐photon‐absorption properties of complexes Ir0 , Ir1 , and L1 . The free ligand ( L1 ) has a relatively small two‐photon absorption cross‐section (δ_max=195 GM), but, when complexed with iridium(III) to afford dinuclear complex Ir1 , it exhibits a higher two‐photon‐absorption cross‐section than ligand L1 in the near‐infrared region and an intense two‐photon‐excited phosphorescent emission. The maximum two‐photon‐absorption cross‐section of Ir1 is 481 GM, which is also significantly larger than that of Ir0 . In addition, because the strong B? F interaction between the dimesitylboryl groups and F^? ions interrupts the extended π‐conjugation, complex Ir1 can be used as an excellent one‐ and two‐photon‐excited “ON–OFF” phosphorescent probe for F^? ions.     

Random multiacceptor poly(2,7‐carbazole) derivatives containing the pentacyclic lactam acceptor unit TPTI for bulk heterojunction solar cells

Here, a family of donor/acceptor (D/A) alternating copolymers and random two‐acceptor and three‐acceptor copolymers were synthesized via Suzuki polymerization based on heptadecan‐9‐yl substituted carbazole as a donor and 4,7‐Bis(5‐bromothiophene‐2‐yl)benzo[c][1,2,5]thiadiazole (DTBT), 2,5‐diethylhexyl‐3,6‐bis(5‐bromothiophene‐2‐yl)pyrrolo[3,4‐c]‐pyrrole‐1,4‐dione (DPP) and 2,8‐dibromo‐4,10‐bis(2‐ethylhexyl)thieno[2′,3′:5,6] pyrido[3,4‐g]thieno[3,2‐c]isoquinoline‐5,11(4H,10H)‐dione (TPTI) as acceptors. For the first time, a relatively new electron‐deficient TPTI unit was used as an acceptor in carbazole‐based conjugated polymers. Introduction of the electron‐deficient TPTI unit into the polymer backbone increased the open‐circuit voltage (V_oc) of the resulting polymer solar cells up to 0.96 V. PCTPTI and PCDTBT‐TPTI exhibited external quantum efficiencies (EQE) up to 75%. All random two‐acceptor copolymers showed broadened absorption profiles compared to the D/A alternating analogues. In order to further improve the light absorption, a random three‐acceptor copolymer was synthesized for the first time, resulting in the broadest absorption in the range of 350–750 nm. Highest occupied molecular orbital (HOMO) energies and V_oc values of the resulting polymers could be successfully tuned by introducing different monomer units into the polymer backbone in different ratios. These results indicate that TPTI is a promising acceptor unit for conjugated polymers and that the random copolymer approach is a successful tool for fine tuning of polymer properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2781–2786     

Highly Efficient Multiphoton‐Pumped Frequency‐Upconversion Stimulated Blue Emission with Ultralow Threshold from Highly Extended Ladder‐Type Oligo(p‐phenylene)s

A series of highly extended π‐conjugated ladder‐type oligo(p‐phenylene)s containing up to 10 phenyl rings with (L)‐Ph(n)‐NPh (n=7–10) or without diphenylamino endcaps (L)‐Ph(n) (n=7 and 8) were synthesized and investigated for their multiphoton absorption properties for frequency upconverted blue ASE/lasing. Extremely large two‐photon absorption (2PA) cross‐sections and highly efficient 2PA ASE/lasing with ultralow threshold were achieved. (L)‐Ph(10)‐NPh exhibits the highest intrinsic 2PA cross‐section of 3643 GM for a blue emissive organic fluorophore reported so far. The record‐high 2PA pumped ASE/lasing efficiency of 2.06 % was obtained by un‐endcapped oligomer, (L)‐Ph(8) rather than that with larger σ₂, suggesting that a molecule with larger σ₂ is not guaranteed to exhibit higher η₂. All of these oligomers exhibit exceptionally ultralow 2PA pumped ASE/lasing thresholds, among which the lowest 2PA pumped threshold of circa 0.26 μJ was achieved by (L)‐Ph(10)‐NPh.     

Ladder‐Type Nonacyclic Arene Bis(thieno[3,2‐b]thieno)cyclopentafluorene as a Promising Building Block for Non‐Fullerene Acceptors

The ladder‐type nonacyclic arene (bis(thieno[3,2‐b]thieno)cyclopentafluorene (BTTF)) has been designed and synthesized through fusing thienothiophenes with the fluorene core from the synthon of dimethyl 9,9‐dioctyl‐2,7‐bis(thieno[3,2‐b]thiophen‐2‐yl)fluorene‐3,6‐dicarboxylate. With BTTF as the central donor unit, a novel acceptor–donor–acceptor (A‐D‐A) type non‐fullerene small‐molecule acceptor ( BTTFIC ) was prepared with 1,1‐dicyanomethylene‐3‐indanones (IC) as the peripheral acceptor units. The energy level of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of BTTFIC locate at ?5.56 and ?3.95 eV, respectively, presenting a low optical band gap of 1.58 eV. Encouragingly, polymer solar cells based on the blends of BTTFIC with both the representative wide‐ and low‐bandgap polymer donors (PBDB‐T, 1.82 eV. PTB7‐Th, 1.58 eV) offer power conversion efficiencies over 8 % (8.78±0.18 % for PBDB‐T: BTTFIC and 8.18±0.29 % for PTB7‐Th: BTTFIC ). These results highlight the advantage of ladder‐type BTTF on the preparation of nonfullerene acceptors with extended conjugated backbones.     

Energy Transfer in Aminonaphthalimide‐Boron‐Dipyrromethene (BODIPY) Dyads upon One‐ and Two‐Photon Excitation: Applications for Cellular Imaging

Aminonaphthalimide–BODIPY energy transfer cassettes were found to show very fast (k_EET≈10¹⁰–10¹¹ s^?1) and efficient BODIPY fluorescence sensitization. This was observed upon one‐ and two‐photon excitation, which extends the application range of the investigated bichromophoric dyads in terms of accessible excitation wavelengths. In comparison with the direct excitation of the BODIPY chromophore, the two‐photon absorption cross‐section δ of the dyads is significantly incremented by the presence of the aminonaphthalimide donor [δ≈10 GM for the BODIPY versus 19–26 GM in the dyad at λ_exc=840 nm; 1 GM (Goeppert–Mayer unit)=10^?50 cm⁴ s molecule^?1 photon^?1]. The electronic decoupling of the donor and acceptor, which is a precondition for the energy transfer cassette concept, was demonstrated by time‐dependent density functional theory calculations. The applicability of the new probes in the one‐ and two‐photon excitation mode was demonstrated in a proof‐of‐principle approach in the fluorescence imaging of HeLa cells. To the best of our knowledge, this is the first demonstration of the merging of multiphoton excitation with the energy transfer cassette concept for a BODIPY‐containing dyad.     

Multi‐Photon Absorption in Metal–Organic Frameworks

Multi‐photon absorption (MPA) is among the most prominent nonlinear optical (NLO) effects and has applications, for example in telecommunications, defense, photonics, and bio‐medicines. Established MPA materials include dyes, quantum dots, organometallics and conjugated polymers, most often dispersed in solution. We demonstrate how metal–organic frameworks (MOFs), a novel NLO solid‐state materials class, can be designed for exceptionally strong MPA behavior. MOFs consisting of zirconium‐ and hafnium‐oxo‐clusters and featuring a chromophore linker based on the tetraphenylethene (TPE) molecule exhibit record high two‐photon absorption (2PA) cross‐section values, up to 3600 GM. The unique modular building‐block principle of MOFs allows enhancing and optimizing their MPA properties in a theory‐guided approach by combining tailored charge polarization, conformational strain, three‐dimensional arrangement, and alignment of the chromophore linkers in the crystal.     

Alternating narrow band gap copolymers derived from indeno[1,2‐b]fluorene and thiophene‐cored‐thieno[3,4‐b]pyrazine derivatives—Synthesis,characterization and comparative studies of photochemical stability

Alternating narrow band gap (NBG) conjugated polymers derived from 6,6′,12,12′‐tetraoctylindeno[1,2‐b]fluorene (IF) and 2,3‐dimethyl‐5,7‐dithien‐2‐yl‐thieno[3,4‐b]pyrazine (DTTP), 2,3‐diphenyl‐5,7‐dithien‐2‐yl‐thieno[3,4‐b]pyrazine (DPTP) or 2,3‐dioctyl‐5,7‐dithien‐2‐yl‐thieno[3,4‐b]pyrazine (DOTP), named as PIF‐DTTP, PIF‐DPTP, and PIF‐DOTP, respectively, were synthesized by Suzuki coupling reaction and characterized. The photochemical stabilities of the copolymers and copolymer derived from IF and 5,7‐dithien‐2‐yl‐thieno[3,4‐b]pyrazine (DTP) were investigated by the UV absorptions, PL spectra, FT‐IR spectra, and photovoltaic properties of the copolymers as a function of UV irradiation time. The studies revealed that the degradation of thieno[3,4‐b]pyrazine (TP) ring under UV irradiation can be retarded or eliminated by introducing phenyl group into the 2,3‐positions of TP ring, and indicated that 2,3‐diphenylthieno[3,4‐b]pyrazine could be used as durable electron deficient moiety to achieve donor–acceptor NBG‐conjugated polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Covalent Organic Framework for Improving Near‐Infrared Light Induced Fluorescence Imaging through Two‐Photon Induction

Fluorescent materials exhibiting two‐photon induction (TPI) are used for nonlinear optics, bioimaging, and phototherapy. Polymerizations of molecular chromophores to form π‐conjugated structures were hindered by the lack of long‐range ordering in the structure and strong π–π stacking between the chromophores. Reported here is the rational design of a benzothiadiazole‐based covalent organic framework (COF) for promoting TPI and obtaining efficient two‐photon induced fluorescence emissions. Characterization and spectroscopic data revealed that the enhancement in TPI performance is attributed to the donor‐π‐acceptor‐π‐donor configuration and regular intervals of the chromophores, the large π‐conjugation domain, and the long‐range order of COF crystals. The crystalline structure of TPI‐COF attenuates the π–π stacking interactions between the layers, and overcomes aggregation‐caused emission quenching of the chromophores for improving near‐infrared two‐photon induced fluorescence imaging.     

Relationship between the liquid crystallinity and field‐effect‐transistor behavior of fluorene–thiophene‐based conjugated copolymers

A series of fluorene–thiophene‐based semiconducting materials, poly(9,9′‐dioctylfluorene‐alt‐α,α′‐bisthieno[3,2‐b]thiophene) (F8TT2), poly(9,9′‐di(3,6‐dioxaheptyl)fluorene‐alt‐thieno[3,2‐b]thiophene) (BDOHF8TT), poly(9,9′‐di(3,6‐dioxaheptyl)fluorene‐alt‐bithiophene) (BDOHF8T2), and poly(9,9′‐dioctylfluorene‐co‐bithiophene‐co‐[4‐(2‐ethylhexyloxyl)phenyl]diphenylamine) (F8T2TPA), was synthesized through a palladium‐catalyzed Suzuki coupling reaction. F8TT2, BDOHF8TT, BDOHF8T2, and F8T2TPA films exhibited photoluminescence maxima at 523, 550, 522, and 559 nm, respectively. Solution‐processed field‐effect transistors (FETs) fabricated with all the copolymers except F8T2TPA showed p‐type organic FET characteristics. Studies of the differential scanning calorimetry scans and FETs of the polymers revealed that more crystalline polymers gave better FET device performance. The greater planarity and rigidity of thieno[3,2‐b]thiophene in comparison with bithiophene resulted in higher crystallinity of the polymer backbone, which led to improved FET performance. On the other hand, the random incorporation of the triphenylamine moiety into F8T2TPA caused the polymer chains to lose crystallinity, resulting in an absence of FET characteristics. With this study, we could assess the liquid‐crystallinity dependence of the field‐effect carrier mobility on organic FETs based on liquid‐crystalline copolymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4709–4721, 2006     

Water‐Soluble Triarylborane Chromophores for One‐ and Two‐Photon Excited Fluorescence Imaging of Mitochondria in Cells

Three water‐soluble tetracationic quadrupolar chromophores comprising two three‐coordinate boron π‐acceptor groups bridged by thiophene‐containing moieties were synthesised for biological imaging applications. Compound 3 containing the bulkier 5‐(3,5‐Me₂C₆H₂)‐2,2′‐(C₄H₂S)₂‐5′‐(3,5‐Me₂C₆H₂) bridge is stable over a long period of time, exhibits a high fluorescence quantum yield and strong one‐ and two‐photon absorption (TPA), and has a TPA cross section of 268 GM at 800 nm in water. Confocal laser scanning fluorescence microscopy studies in live cells indicated localisation of the chromophore at the mitochondria; moreover, cytotoxicity measurements proved biocompatibility. Thus, chromophore 3 has excellent potential for one‐ and two‐photon‐excited fluorescence imaging of mitochondrial function in cells.     

Synthesis,photophysics, theoretical modeling,and electroluminescence of novel 2,7‐carbazole‐based conjugated polymers with sterically hindered structures

2,7‐dibromo‐N‐hexylcarbazole is successfully synthesized in three steps with an overall 37% yield. Novel 2,7‐carbazole‐based sterically hindered conjugated polymers are further synthesized. In the backbone structure of polymer P1 , alkylated bithiophene moiety is β‐substituted with dodecyl chains on both thiophene rings, adopting the tail‐to‐tail configuration. While for polymers P2 and P3 , partially planarized thieno[3,2‐b]thiophene moiety ( P2 ) and β‐pentyl substituted thieno[3,2‐b]thiophene ( P3 ) are incorporated. All polymers demonstrate efficient blue‐to‐green light emission, good thermal stability (T_d ≥ 379 °C), and high glass transition temperatures (T_g = 118 °C). The optical and electronic properties of the resulted polymers are tuned by the incorporated alkyl chains. For instance, the incorporation of β‐pentyl group in thieno[3,2‐b]thiophene moiety endows P3 with blue‐shifted photophysical spectra, reduced fluorescence quantum yield and larger band gap in comparison with P2 . The steric effect of incorporated alkyl chains is further illustrated by geometry optimization of three model oligomers (analogues to the repetition units of P1–P3 ) using density functional theory. Sterically hindered polymers P1 and P2 exhibit high charge transport ability and moderate electroluminescent properties in primarily tested single‐layer light‐emitting diodes (configuration: ITO/PEDOT:PSS/Polymer/Ca/Ag). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7725–7738, 2008     

Synthesis,characterization, and photovoltaic properties of novel conjugated copolymers derived from phenothiazines

Two novel series of soluble alternating conjugated copolymers comprising 10‐alkylphenothiazine and bithiophene or 3‐pentylthieno[3,2‐b]thiophene moieties were synthesized using palladium‐catalyzed Suzuki coupling reaction. The structures of the polymers and their thermal, photophysical, electrochemical, and photovoltaic properties were characterized and investigated. The polymers exhibited good thermal stability with decomposition temperature in the region of 342–390 °C and their glass transition temperatures (T_g) ranging from 126 to 150 °C. All polymers demonstrate broad optical absorption in the region of 300–500 nm with efficient blue‐green light emission. They showed ambipolar redox properties with low HOMO levels around ?5.13 eV. Polymer solar cells were fabricated using blends of the copolymers and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) in a 1:1 weight ratio. The maximum power conversion efficiency (η = 0.24%) was measured for the poly[3,7‐ (10‐hexylphenothiazine)‐alt‐bithiophene] as donor under simulated sun light (1000 W/m²). Open circuit voltages of up to 0.8 V have been obtained. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5266–5276, 2007     

Two‐Photon Absorption Properties of Dehydrobenzo[12]annulenes and Hexakis(phenylethynyl)benzenes: Effect of Edge‐Linkage

Two‐photon absorption (TPA) properties of two trefoil‐shaped compounds with different edge linkages—tris(hexadehydrotribenzo[12]annulene) and tris(tetradehydrotribenzo[12]annulene)—and three asterisk‐shaped compounds having no edge‐linkage—hexakis(phenylethynyl)benzenes—are investigated experimentally by the open‐aperture Z‐scan and TPA‐induced fluorescence methods with wavelength tuneable femtosecond pulses. The compound with ethynylene edge‐linkage exhibits the most intense TPA (the maximal TPA cross section is 1300±170 GM at 572 nm where 1 GM=10^?50 cm⁴ s molecule^?1 photon^?1). The TPA activity of the compounds is primarily explained in terms of the planarity of the molecules in relation with the type of edge‐linkage.