Ultrafast Photoinduced Energy and Electron Transfer in Multi‐Modular Donor–Acceptor Conjugates

New multi‐modular donor–acceptor conjugates featuring zinc porphyrin (ZnP), catechol‐chelated boron dipyrrin (BDP), triphenylamine (TPA) and fullerene (C₆₀), or naphthalenediimide (NDI) have been newly designed and synthesized as photosynthetic antenna and reaction‐center mimics. The X‐ray structure of triphenylamine‐BDP is also reported. The wide‐band capturing polyad revealed ultrafast energy‐transfer (k_ENT=1.0×10¹² s^?1) from the singlet excited BDP to the covalently linked ZnP owing to close proximity and favorable orientation of the entities. Introducing either fullerene or naphthalenediimide electron acceptors to the TPA‐BDP‐ZnP triad through metal–ligand axial coordination resulted in electron donor–acceptor polyads whose structures were revealed by spectroscopic, electrochemical and computational studies. Excitation of the electron donor, zinc porphyrin resulted in rapid electron‐transfer to coordinated fullerene or naphthalenediimide yielding charge separated ion‐pair species. The measured electron transfer rate constants from femtosecond transient spectral technique in non‐polar toluene were in the range of 5.0×10⁹–3.5×10¹⁰ s^?1. Stabilization of the charge‐separated state in these multi‐modular donor–acceptor polyads is also observed to certain level.     

Axially Substituted Silicon Phthalocyanine as Electron Donor in a Dyad and Triad with Azafullerene as Electron Acceptor for Photoinduced Charge Separation

The synthesis of a donor–acceptor silicon phthalocyanine (SiPc)‐azafullerene (C₅₉N) dyad 1 and of the first acceptor–donor–acceptor C₅₉N‐SiPc‐C₅₉N dumbbell triad 2 was accomplished. The two C₅₉N‐based materials were comprehensively characterized with the aid of NMR spectroscopy, MALDI‐MS as well as DFT calculations and their redox and photophysical properties were evaluated with CV and steady‐state and time‐resolved absorption and photoluminescence spectroscopy measurements. Notably, femtosecond transient absorption spectroscopy assays revealed that both dyad 1 and triad 2 undergo, after selective photoexcitation of the SiPc moiety, photoinduced electron transfer from the singlet excited state of the SiPc moiety to the azafullerene counterpart to produce the charge‐separated state, with lifetimes of 660 ps, in the case of dyad 1 , and 810 ps, in the case of triad 2 . The current results are expected to have significant implications en route to the design of advanced C₅₉N‐based donor–acceptor systems targeting energy conversion applications.     

Vectorial Electron Transfer in Donor–Photosensitizer–Acceptor Triads Based on Novel Bis‐tridentate Ruthenium Polypyridyl Complexes

The first examples of rodlike donor–photosensitizer–acceptor arrays based on bis‐2,6‐di(quinolin‐8‐yl)pyridine Ru^II complexes 1 a and 3 a for photoinduced electron transfer have been synthesized and investigated. The complexes are synthesized in a convergent manner and are isolated as linear, single isomers. Time‐resolved absorption spectroscopy reveals long‐lived, photoinduced charge‐separated states (τ_CSS ( 1 a )=140 ns, τ_CSS ( 3 a )=200 ns) formed by stepwise electron transfer. The overall yields of charge separation (≥50 % for complex 1 a and ≥95 % for complex 3 a ) are unprecedented for bis‐tridentate Ru^II polypyridyl complexes. This is attributed to the long‐lived excited state of the [Ru(dqp)₂]²⁺ complex combined with fast electron transfer from the donor moiety following the initial charge separation. The rodlike arrangement of donor and acceptor gives controlled, vectorial electron transfer, free from the complications of stereoisomeric diversity. Thus, such arrays provide an excellent system for the study of photoinduced electron transfer and, ultimately, the harvesting of solar energy.     

Circular Photoinduced Electron Transfer in a Donor‐Acceptor‐Acceptor Triad

An electron‐donor‐acceptor‐acceptor (D‐A₁‐A₂) triad has been developed that provides the first proof‐of‐concept for a photoinitiated molecular circuit. After photoexcitation into an optical charge‐transfer transition between D and A₁, subsequent thermal electron‐transfer from A₁^.? to A₂ is followed by geometric rearrangement in the D^.+‐A₁‐A₂^.? charge‐separated state to form an ion‐pair contact. This facilitates “forward” charge recombination between A₂^.? and D^.+ to complete the molecular circuit with an estimated quantum efficiency of 4 % in toluene at 298 K.     

Tetrathiafulvalene‐Fused Porphyrins via Quinoxaline Linkers: Symmetric and Asymmetric Donor–Acceptor Systems

A tetrathiafulvalene (TTF) donor is annulated to porphyrins (P) via quinoxaline linkers to form novel symmetric P–TTF–P triads 1 a – c and asymmetric P–TTF dyads 2 a , b in good yields. These planar and extended π‐conjugated molecules absorb light over a wide region of the UV/Vis spectrum as a result of additional charge‐transfer excitations within the donor–acceptor assemblies. Quantum‐chemical calculations elucidate the nature of the electronically excited states. The compounds are electrochemically amphoteric and primarily exhibit low oxidation potentials. Cyclic voltammetric and spectroelectrochemical studies allow differentiation between the TTF and porphyrin sites with respect to the multiple redox processes occurring within these molecular assemblies. Transient absorption measurements give insight into the excited‐state events and deliver corresponding kinetic data. Femtosecond transient absorption spectra in benzonitrile may suggest the occurrence of fast charge separation from TTF to porphyrin in dyads 2 a , b but not in triads 1 a – c . Clear evidence for a photoinduced and relatively long lived charge‐separated state (385 ps lifetime) is obtained for a supramolecular coordination compound built from the ZnP–TTF dyad and a pyridine‐functionalized C₆₀ acceptor unit. This specific excited state results in a (ZnP–TTF)^?+ ??? (C₆₀py)^?? state. The binding constant of Zn^II ??? py is evaluated by constructing a Benesi–Hildebrand plot based on fluorescence data. This plot yields a binding constant K of 7.20×10⁴ M ^?1, which is remarkably high for bonding of pyridine to ZnP.     

Ultrafast Photoinduced Charge Separation Leading to High‐Energy Radical Ion‐Pairs in Directly Linked Corrole–C60 and Triphenylamine–Corrole‐C60 Donor–Acceptor Conjugates

Closely positioned donor–acceptor pairs facilitate electron‐ and energy‐transfer events, relevant to light energy conversion. Here, a triad system TPACor‐C₆₀ , possessing a free‐base corrole as central unit that linked the energy donor triphenylamine ( TPA ) at the meso position and an electron acceptor fullerene (C₆₀) at the β‐pyrrole position was newly synthesized, as were the component dyads TPA‐Cor and Cor‐C₆₀ . Spectroscopic, electrochemical, and DFT studies confirmed the molecular integrity and existence of a moderate level of intramolecular interactions between the components. Steady‐state fluorescence studies showed efficient energy transfer from ¹ TPA* to the corrole and subsequent electron transfer from ¹corrole* to fullerene. Further studies involving femtosecond and nanosecond laser flash photolysis confirmed electron transfer to be the quenching mechanism of corrole emission, in which the electron‐transfer products, the corrole radical cation ( Cor^?+ in Cor‐C₆₀ and TPA‐Cor^?+ in TPACor‐C₆₀ ) and fullerene radical anion (C₆₀^??), could be spectrally characterized. Owing to the close proximity of the donor and acceptor entities in the dyad and triad, the rate of charge separation, k_CS, was found to be about 10¹¹ s^?1, suggesting the occurrence of an ultrafast charge‐separation process. Interestingly, although an order of magnitude slower than k_CS, the rate of charge recombination, k_CR, was also found to be rapid (k_CR≈10¹⁰ s^?1), and both processes followed the solvent polarity trend DMF>benzonitrile>THF>toluene. The charge‐separated species relaxed directly to the ground state in polar solvents while in toluene, formation of ³corrole* was observed, thus implying that the energy of the charge‐separated state in a nonpolar solvent is higher than the energy of ³corrole* being about 1.52 eV. That is, ultrafast formation of a high‐energy charge‐separated state in toluene has been achieved in these closely spaced corrole–fullerene donor–acceptor conjugates.     

Synthesis and Characterization of Donor–π‐Acceptor‐Based Porphyrin Sensitizers: Potential Application of Dye‐Sensitized Solar Cells

New porphyrin sensitizers based on donor–π‐acceptor (D‐π‐A) approach have been designed, synthesized, characterized by various spectroscopic techniques and their photovoltaic properties explored. N,N′‐Diphenylamine acts as donor, the porphyrin is the π‐spacer, and either carboxylic acid or cyanoacryclic acid acts as acceptor. All compounds were characterized by using ¹H NMR spectroscopy, ESI‐MS, UV–visible emission spectroscopies as well as electrochemical methods. The presence of aromatic groups between porphyrin π‐plane and acceptor group push the absorption of both Soret and Q‐bands of porphyrin towards the red region. The electrochemical properties suggests that LUMO of these sensitizers above the TiO₂ conduction band. Finally, the device was fabricated using liquid redox electrolyte (I^?/I₃^?) and its efficiency was compared with that of a leading sensitizer.     

Synthesis and optoelectronic characterization of poly(fluorenylethynylene)s containing perylene bisimide moiety in the backbone

A series of poly(fluorenylethynylene)s containing different ratios of perylene bisimide moiety in the backbone were synthesized by Sonogashira cross‐coupling reaction. The electron‐deficient perylene bisimide moiety was introduced into the backbone to construct the donor‐acceptor architectures. The chemical structures of these copolymers were determined by ¹H NMR and FTIR. The solubility, thermal, and optoelectronic properties were studied. The results of UV–vis absorption and fluorescence spectra of these copolymers showed that intramolecular energy transfer and charge separation occur between the fluorenyl alkyne segment and perylene bisimide moiety. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1932–1938, 2008     

“Two‐Point” Self‐Assembly and Photoinduced Electron Transfer in meso‐Donor‐Carrying Bis(styryl crown ether)‐BODIPY–Bis(alkylammonium)fullerene Donor–Acceptor Conjugates

BF₂‐chelated dipyrromethene, BODIPY, was functionalized to carry two styryl crown ether tails and a secondary electron donor at the meso position. By using a “two‐point” self‐assembly strategy, a bis‐alkylammonium‐functionalized fullerene (C₆₀) was allowed to self‐assemble the crown ether voids of BODIPY to obtain multimodular donor–acceptor conjugates. As a consequence of the two‐point binding, the 1:1 stoichiometric complexes formed yielded complexes of higher stability in which fluorescence of BODIPY was found to be quenched; this suggested the occurrence of excited‐state processes. The geometry and electronic structure of the self‐assembled complexes were derived from B3LYP/3‐21G(*) methods in which no steric constraints between the entities was observed. An energy‐level diagram was established by using spectral, electrochemical, and computational results to help understand the mechanistic details of excited‐state processes originating from ¹bis‐styryl‐BODIPY*. Femtosecond transient absorbance studies were indicative of the formation of an exciplex state prior to the charge‐separation process to yield a bis‐styryl‐BODIPY ^{. +}–C₆₀ ^{. −} radical ion pair. The time constants for charge separation were generally lower than charge‐recombination processes. The present studies bring out the importance of multimode binding strategies to obtain stable self‐assembled donor–acceptor conjugates capable of undergoing photoinduced charge separation needed in artificial photosynthetic applications.     

Probing Supramolecular Interactions between a Crown Ether Appended Zinc Phthalocyanine and an Ammonium Group Appended to a C60 Derivative

Self‐assembly driven by crown ether complexation of zinc phthalocyanines equipped with one 18‐crown‐6 moiety and fullerenes bearing an ammonium head group afforded a novel donor–acceptor hybrid. In reference experiments, fullerenes containing a Boc‐protected amine functionality have been probed. The circumvention of zinc phthalocyanine aggregation is important for the self‐assembly, which required the addition of pyridine. From absorption and fluorescence titration assays, which provided sound and unambiguous evidence for mutual interactions between the electron donor and the electron acceptor within the hybrids, association constants in the order of 8.0×10⁵ m ^?1 have been derived. The aforementioned is based on 1:1 stoichiometries, which have been independently confirmed by Job's plot measurements. In the excited state, which has been examined by transient absorption experiments, intermolecular charge separation evolves from the photoexcited zinc phthalocyanine to the fullerene subunit and leads to short‐lived charge‐separated states. Interestingly, photoexcitation of zinc phthalocyanine dimers/aggregates can also be followed by an intermolecular charge separation between vicinal phthalocyanines. These multicomponent supramolecular ensembles have also been shown by in‐depth electrospray ionization mass spectrometry (ESI‐MS) studies, giving rise to the formation and detection of a variety of non‐covalently linked species.     

Bipyridinium Polymers That Dock Tetrathiafulvalene Guests in Water Driven by Donor–Acceptor and Ion Pair Interactions

Two water‐soluble para‐xylylene‐connected 4,4′‐bipyridinium (BIPY²⁺) polymers have been prepared. UV‐Vis absorption, ¹H NMR spectroscopy, and cyclic voltammetry experiments support that in water the BIPY²⁺ units in the polymers form stable 1:1 charge‐transfer complexes with tetrathiafulvalene (TTF) guests that bear two or four carboxylate groups. These charge‐transfer complexes are stabilized by the donor–acceptor interaction between electron‐rich TTF and electron‐deficient BIPY²⁺ units and electrostatic attraction between the dicationic BIPY²⁺ units and the anionic carboxylate groups attached to the TTF core. On the basis of UV‐Vis experiments, a lower limit to the apparent association constant of the TTF?BIPY²⁺ complexes of the mixtures, 1.8×10⁶ m ^?1, has been estimated in water. Control experiments reveal substantially reduced binding ability of the neutral TTF di‐ and tetracarboxylic acids to the BIPY²⁺ molecules and polymers. Moreover, the stability of the charge‐transfer complexes formed by the BIPY²⁺ units of the polymers are considerably higher than that of the complexes formed between two monomeric BIPY²⁺ controls and the dicarboxylate‐TTF donor; this has been attributed to the mutually strengthened electron‐deficient nature of the BIPY²⁺ units of the polymers due to the electron‐withdrawing effect of the BIPY²⁺ units.     

Kinetic Studies of Donor–Acceptor Cyclopropanes: The Influence of Structural and Electronic Properties on the Reactivity

The kinetics of (3+2) cycloaddition reactions of 18 different donor–acceptor cyclopropanes with the same aldehyde were studied by in situ NMR spectroscopy. Increasing the electron density of the donor residue accelerates the reaction by a factor of up to 50 compared to the standard system (donor group=phenyl), whereas electron‐withdrawing substituents slow down the reaction by a factor up to 660. This behavior is in agreement with the Hammett substituent parameter σ. The obtained rate constants from the (3+2) cycloadditions correlate well with data from additionally studied (3+n) cycloadditions with a nitrone (n=3) and an isobenzofuran (n=4). A comparison of the kinetic data with the bond lengths in the cyclopropane (obtained by X‐ray diffraction and computation), or the ¹H and ¹³C NMR shifts, revealed no correlation. However, the computed relaxed force constants of donor–acceptor cyclopropanes proved to be a good indicator for the reactivity of the three‐membered ring.     

Long‐Lived,Directional Photoinduced Charge Separation in RuII Complexes Bearing Laminate Polypyridyl Ligands

Ru^II complexes incorporating both amide‐linked bithiophene donor ancillary ligands and laminate acceptor ligands; dipyrido[3,2‐a:2′,3′‐c]phenazine (dppz), tetrapyrido[3,2‐a:2′,3′‐c:3′′,2′′‐h:2′′′,3′′′‐j]phenazine (tpphz), and 9,11,20,22‐tetraazatetrapyrido[3,2‐a:2′,3′‐c:3′′,2′′‐l:2′′′,3′′′]‐pentacene (tatpp) exhibit long‐lived charge separated (CS) states, which have been analyzed using time‐resolved transient absorption (TA), fluorescence, and electronic absorption spectroscopy in addition to ground state electrochemical and spectroelectrochemical measurements. These complexes possess two electronically relevant ³MLCT states related to electron occupation of MOs localized predominantly on the proximal “bpy‐like” portion and central (or distal) “phenazine‐like” portion of the acceptor ligand as well as energetically similar ³LC and ³ILCT states. The unusually long excited state lifetimes (τ up to 7 μs) observed in these complexes reflect an equilibration of the ³MLCT_prox or ³MLCT_dist states with additional triplet states, including a ³LC state and a ³ILCT state that formally localizes a hole on the bithiophene moiety and an electron on the laminate acceptor ligand. Coordination of a Zn^II ion to the open coordination site of the laminate acceptor ligand is observed to significantly lower the energy of the ³MLCT_dist state by decreasing the magnitude of the excited state dipole and resulting in much shorter excited state lifetimes. The presence of the bithiophene donor group is reported to substantially extend the lifetime of these Zn adducts via formation of a ³ILCT state that can equilibrate with the ³MLCT_dist state. In tpphz complexes, Zn^II coordination can reorder the energy of the ³MLCT_prox and ³MLCT_dist states such that there is a distinct switch from one state to the other. The net result is a series of complexes that are capable of forming CS states with electron–hole spatial separation of up to 14 Å and possess exceptionally long lifetimes by equilibration with other triplet states.     

Coordinative Interactions between Porphyrins and C60, La@C82, and La2@C80

For the first time, a C₆₀ derivative ( 1 ) and two different lanthanum metallofullerene derivatives, La@C₈₂Py ( 2 ) and La₂@C₈₀Py ( 3 ), that feature a pyridyl group as a coordination site for transition‐metal ions have been synthesized and integrated as electron acceptors into coordinative electron‐donor/electron‐acceptor hybrids. Zinc tetraphenylporphyrin ( ZnP ) served as an excited‐state electron donor in this respect. Our investigations, by means of steady‐state and time‐resolved photophysical techniques found that electron transfer governs the excited‐state deactivation in all of these systems, namely 1/ZnP , 2/ZnP , and 3/ZnP , whereas, in the ground state, notable electronic interactions are lacking. Variation of the electron‐accepting fullerene or metallofullerene moieties provides the incentive for fine‐tuning the binding constants, the charge‐separation kinetics, and the charge‐recombination kinetics. To this end, the binding constants, which ranged from log K_assoc=3.94–4.38, are dominated by axial coordination, with minor contributions from the orbital overlap of the curved and planar π systems. The charge‐separation and charge‐recombination kinetics, which are in the order of 10¹⁰ and 10⁸ s^?1, relate to the reduction potential of the fullerene and metallofullerenes, respectively.     

Exceptional Blueshifted and Enhanced Aggregation‐Induced Emission of Conjugated Asymmetric Triazines and Their Applications in Superamplified Detection of Explosives

A novel conjugated asymmetric donor–acceptor (CADA) strategy for preventing the redshift in photoluminescence, as well as preserving the merits of donor–acceptor architectures, was proposed and demonstrated for two triazine derivatives, which showed highly efficient, narrow, and blueshifted ultraviolet light emission in solid films along with special aggregation‐induced emission behavior. A mechanism of aggregation‐induced locally excited‐state emission by suppressing the twisted intramolecular charge‐transfer emission for the spectacular optoelectronic phenomena of these CADA molecules was suggested on the basis of both experimental measurements and theoretical calculations. By taking advantage of this special CADA architecture, fluorescent probes based on aggregates of conjugated asymmetric triazines in THF/water for the detection of explosives show superamplified detection of picric acid with high quenching constants (>1.0×10⁷ M ^?1) and a low detection limit of 15 ppb.     

Carborane Dyads for Photoinduced Electron Transfer: Photophysical Studies on Carbazole and Phenyl‐o‐carborane Molecular Assemblies

o‐Carborane‐based donor–acceptor dyads comprising an o‐carboranyl phenyl unit combined with N‐carbazole ( 1 ) or 4‐phenyl‐N‐carbazole ( 2 ) were prepared, and their dyad characters were confirmed by steady‐state photochemistry and photodynamic experiments as well as electrochemical studies. The absorption and electrochemical properties of the dyads were essentially the sum of those of the carbazole and o‐carboranyl phenyl units; this indicates negligible interaction between the carbazole and o‐carborane units in the ground state. However, the emission spectra of 1 and 2 indicated that carbazole fluorescence was effectively quenched and a new charge‐transfer (CT) emission was observed in solvents, varying from hexane to acetonitrile, which exhibited large Stoke shifts. The CT emission properties of o‐carborane‐based dyads were further analyzed by using Lippert–Mataga plots to show that unit charge separation occurred to form a charge‐separated species in the excited state, namely, 1?2 . This excited‐state species was confirmed by nanosecond transient absorption spectra and spectroelectrochemical measurements; the photoexcitation of carbazole generated the CT state in which a radical cation and anion were formed at the carbazole and o‐carborane units, respectively, within a few nanoseconds. DFT calculations corroborated the presence of this CT species and showed localized populations of the highest singly occupied molecular orbital on 2 in the reduced anionic state. As a result, molecular assemblies formed by linking the carbazole group with the o‐carborane cage through a phenylene or multi‐phenylene spacer revealed that the photoinduced electron‐transfer process occurred intramolecularly.     

Halogen‐Bonded Supramolecular Capsules in the Solid State,in Solution,and in the Gas Phase

Supramolecular capsules were assembled by neutral halogen bonding (XB) and studied in the solid state, in solution, and in the gas phase. The geometry of the highly organized capsules is shown by an X‐ray crystal structure which features the assembly of two XB hemispheres, geometrically rigidified by H‐bonding to eight MeOH molecules and encapsulation of two benzene guests. To enhance capsular association strength, tuning the XB donor is more efficient than tuning the XB acceptor, due to desolvation penalties in protic solvents, as shown for a tetraquinuclidine XB acceptor hemisphere. With a tetra(iodoethynyl) XB donor and a tetralutidine XB acceptor, the association in deuterated benzene/acetone/methanol 70:30:1 at 283 K reaches K _a=(2.11±0.39)×10⁵ m ⁻¹ (ΔG =−6.9±0.1 kcal mol⁻¹). The stability of the XB capsules in the gas phase was confirmed by electrospray ionization mass spectrometry (ESI‐MS). A new guest binding site was uncovered within the elongated iodoethynyl capsule.     

The Importance of Excited‐State Energy Alignment for Efficient Exciplex Systems Based on a Study of Phenylpyridinato Boron Derivatives

Understanding excited‐state dynamics is critical for improving the photoluminescence (PL) efficiency of exciplexes. A series of exciplexes based on conventional hole‐transporting materials as donor and newly developed phenylpyridinato boron derivatives as acceptor were investigated. High PL efficiencies were achieved in only some combinations, and a large difference in performance among combinations provided insight into nonradiative processes in exciplex systems. Furthermore, the triplet local excited states (³LE) of each donor and acceptor were found play an important role in triplet exciplex harvesting. Significant contributions from triplets were clearly observed when the charge‐transfer excited states (¹CT and ³CT) and ³LE were ideally aligned. We also demonstrated fine control of relative energy alignment via the concentration to improve the PL efficiency.     

Self‐Assembled Hexanuclear Organometallic Cages: Synthesis,Characterization, and Host–Guest Properties

A series of iridium‐ and rhodium‐based hexanuclear organometallic cages containing 2,5‐dichloro‐3,6‐dihydroxy‐1,4‐benzoquinone, 9,10‐dihydroxy‐1,4‐anthraquinone, and 6,11‐dihydroxynaphthacene‐5,12‐dione ligands were synthesized from the self‐assembly of the corresponding molecular “clips” and 2,4,6‐tri(4‐pyridyl)‐1,3,5‐triazine ligands in good yields. These organometallic cages can form inclusion systems with a wide variety of π‐donor substrates, including coronene, pyrene, [Pt(acac)₂], and hexamethoxytriphenylene. The 1:1 complexation of the resulting supramolecular assemblies was confirmed by ¹H NMR spectroscopy. Large complexation shifts (Δδ>1 ppm) were observed in the ¹H NMR spectra of guests in the presence of cage [Cp*₆M₆(μ‐DHNA)₃(tpt)₂](OTf)₆ ( 6a ; M=Ir, tpt=2,4,6‐tri(4‐pyridyl)‐1,3,5‐triazine). The formation of discrete 1:1 donor–acceptor complexes, pyrene ?6 b (M=Rh), coronene ?6 a , coronene ?6 b , and [Pt(acac)₂] ?6 a was confirmed by their single‐crystal X‐ray analyses. In these systems, the most important driving force for the formation of guest–host complexes is clearly the donor–acceptor π???π stacking interaction, including charge‐transfer interactions between the electron‐donating and electron‐accepting aromatic components. These structures provide compelling evidence for the existence of strong attractive forces between the electron‐deficient triazine core and electron‐rich guest. The results presented here may provide useful guidance for designing artificial receptors for functional biomolecules.     

Synthesis of Poly(benzothiadiazole‐co‐dithienobenzodithiophenes) and Effect of Thiophene Insertion for High‐Performance Polymer Solar Cells

We describe herein the synthesis of novel donor–acceptor conjugated polymers with dithienobenzodithiophenes (DTBDT) as the electron donor and 2,1,3‐benzothiadiazole as the electron acceptor for high‐performance organic photovoltaics (OPVs). We studied the effects of strategically inserting thiophene into the DTBDT as a substituent on the skeletal structure on the opto‐electronic performances of fabricated devices. From UV/Vis absorption, electrochemical, and field‐effect transistor analyses, we found that the thiophene‐containing DTBDT derivative can substantially increase the orbital overlap area between adjacent conjugated chains and thus dramatically enhance charge‐carrier mobility up to 0.55 cm² V^?1 s^?1. The outstanding charge‐transport characteristics of this polymer allowed the realization of high‐performance organic solar cells with a power conversion efficiency (PCE) of 5.1 %. Detailed studies on the morphological factors that enable the maximum PCE of the polymer solar cells are discussed along with a hole/electron mobility analysis based on the space‐charge‐limited current model.