Ground-state Charge-transfer Complexes Research Articles

Controlled photoinduced electron transfer via triplet in polymer matrix using electrostatic interactions

Drawing inspiration from highly efficient natural photosynthetic systems, we developed an artificial photoinduced electron transfer (PET) system within a poly(N-methyl-4-vinylpyridinium) (P4VPMe) polymer matrix. This system features 5,10,15,20-tetrakis-(4-sulfonatophenyl) porphyrin (TPPS) and its zinc complex (ZnTPPS) as electron donors and methylviologen (MV2+) as the electron acceptor. In the presence of an excess of P4VPMe, ZnTPPS exists as individual molecules rather than self-aggregating, favoring PET. Under these conditions, P4VPMe inhibits the formation of ground-state charge-transfer complex between ZnTPPS and MV2+. This shifts the main PET process from singlet to triplet states. ZnTPPS in an excess of P4VPMe demonstrates over a tenfold increase in catalytic activity for the photoinduced oxidation of MV2+ compared to ZnTPPS alone.

Unveiling the role of a ground state charge transfer complex in carbon nanoparticles for highly efficient metal-free solar hydrogen production

A ground state charge transfer complex of N, P-CNPs and TEOA promotes long-lived free carriers and modifies the electronic energy levels for complete metal-free solar H2 generation. Free TEOA molecules act as effective SEDs during photocatalysis.

A facile and sensitive hexahomotrioxacalix[3]arene-based fluorescent sensor for the detection of trace amounts of 2,4,6-trinitrophenol

Nitroaromatic compounds are common explosives and toxic pollutants, the selective and sensitive detection of which is of great importance. Herein, a facile and sensitive fluorescent sensor L was constructed for the sensing of TNP based on the hexahomotrioxacalix[3]arene skeleton. The fluorescence emission of L was drastically quenched in the presence of 2,4,6-trinitrophenol (TNP), while other tested NACs, metal ions, and anions induced negligible changes. Under the optimized conditions, the spectroscopic studies revealed that L exhibited extremely sensitive and selective TNP recognition, with a detection limit of 9.17 × 10−7 M and a quenching constant of 2.44 × 104 M−1. The sensitivity of sensor L for TNP was attributed to the formation of a ground-state charge-transfer complex and an inner filter effect, which also contributed to the special selectivity of the sensor among the various nitroaromatic analogues. Compared with previous reports, L can serve as a highly efficient sensor for the sensing of TNP and can be employed over a wide pH range of 2 to 12. Sensor L was effectively used to quantify TNP in real water and soil samples. Additionally, fluorescent test strips were also developed for visual and rapid detection of TNP in both the solution and vapour phases.

Sterically-Hindered Molecular p-Dopants Promote Integer Charge Transfer in Organic Semiconductors.

Molecular p-dopants designed to undergo electron transfer with organic semiconductors are typically planar molecules with high electron affinity. However, their planarity can promote the formation of ground-state charge transfer complexes with the semiconductor host and results in fractional instead of integer charge transfer, which is highly detrimental to doping efficiency. Here, we show this process can be readily overcome by targeted dopant design exploiting steric hindrance. To this end, we synthesize and characterize the remarkably stable p-dopant 2,2',2''-(cyclopropane-1,2,3-triylidene)tris(2-(perfluorophenyl)acetonitrile) comprising pendant functional groups that sterically shield its central core while retaining high electron affinity. Finally, we demonstrate it outperforms a planar dopant of identical electron affinity and increases the thin film conductivity by up to an order of magnitude. We believe exploiting steric hindrance represents a promising design strategy towards molecular dopants of enhanced doping efficiency.

Ultra-sensitive fluorescent and colorimetric probes for femtomolar detection of picric acid: Mechanochromic, latent fingerprinting, and pH responsive character with AIE properties

• Probes 1(a-c) were synthesized through one-pot multicomponent reaction. • This study offers design strategy to transform ACQ into AIE feature. • Probes showed mechanochromism, pH responsive, and identification of latent fingerprints. • Probes displayed ultrasensitive femtomolar level sensing of picric acid (PA) • Selective sensing of PA was achieved through the predominant involvement of ground state complexation. Multiple stimuli responsive easy to synthesize organic probes with remarkable structural properties are imminently essential. To this endeavor, 1,4-dihydropyridine (DHP) based three new probes 1(a-c) were successfully synthesized and characterized through modern spectroscopic and mass spectrometry techniques. Planar dihydropyridine was appended with multiple donor-acceptor and rotors to bring aggregation induced emission (AIE) character in probes 1(a-b) . Interestingly, probe 1c displayed aggregation caused quenching (ACQ) effect due to perpendicularly attached naphthyl ring. Therefore, this study presents extensive structure-property relationship to invoke AIE character. Moreover, probes 1(a-c) exhibited high photostability, reversible mechanochromism, pH responsive character, and adequate identification of latent fingerprints (LFPs). Importantly, multifunctional probes 1(a-c) served as highly selective fluorescent and colorimetric probes for picric acid (PA). In solution, highly sensitive femtomolar (fM) level (limit of detection (LOD); 12.3, 14.6, and 27.1 fM) detection of PA was attributed to combined effect of ground-state charge transfer complex formation and Forster resonance energy transfer (FRET). Favorable complexation between probes and PA was proved through UV-visible absorption, density functional theory (DFT), and dynamic light scattering (DLS) studies. Advantageously, probes were able to detect picric acid in vapor phase. In addition, probes were practically applicable for the contact mode detection of PA and sensing of PA in LFPs and industrial samples.

Fluorescein based fluorescent and colorimetric sensors for sensitive detection of TNP explosive in aqueous medium: Application of logic gate

Rapid detection of 2,4,6-trinitrophenol (TNP) in real samples has recently attained considerable attention from the perspective of national security, human health, and environmental safety. In this context, cost-effective and convenient detection of TNP explosive was accomplished through two new fluorescein based sensors F2 and F3. Sensors displayed effective fluorescence quenching response towards TNP in the aqueous medium. Highly sensitive fluorescence detection of TNP explosive (detection limit, 0.73 (F2) and 1.7 nM (F3)) was governed by ground-state charge transfer complex formation, facilitated by favorable H-bonding between sensor and TNP explosive. Fluorescence quenching mechanism for the detection of TNP explosive was investigated through UV–Visible absorption, dynamic light scattering (DLS), density functional theory (DFT) calculations, the Benesi-Hildebrand, and Job’s plots. Advantageously, sensors displayed selective and immediate colorimetric recognition of TNP explosive. Importantly, sensors exhibited quick response time towards TNP even in the presence of potential interferences that make them highly suitable for practical applications. Sensors were successfully applied for fluorescent and colorimetric detection of TNP explosive in industrial water samples and fabrication of logic gates. Further, convenient contact mode and instant surface sensing of TNP explosive were achieved through the fabrication of fluorescent strips and explosive responsive test kits.

Silver(I)-Carbene Bond-Directed Rigidification-Induced Emissive Metallacage for Picric Acid Detection.

A new triphenylamine-based tetraimidazolium salt L was developed for silver(I)-carbene bond-directed synthesis of tetranuclear silver(I) octacarbene ([Ag4(L)2](PF6)4) metallacage 1. Interestingly, after assembly formation, metallacage 1 showed a nine-fold emission enhancement in dilute solution while ligand L was weakly fluorescent. This is attributed to the rigidity induced to the system by metal-carbene bond formation where the metal center acts as a rigidification unit. The enhanced emission intensity in dilute solution and the presence of the triphenylamine core made 1 a potential candidate for recognition of picric acid (PA). This recognition can be ascribed to the dual effect of ground-state charge-transfer complex formation and resonance energy transfer between the picrate and metallacage 1. For metallacage 1, a considerable detection limit toward PA was observed. The use of such metal-carbene bond-directed rigidification-induced enhanced emission for PA sensing is noteworthy.

Self-assembled nanomaterials of naphthalene monoimide in aqueous medium for multimodal detection of picric acid

Picric acid (PA) is a menacing environmental pollutant on account of its high solubility in water. Extensive usage of picric acid as a handy chemical and go-to explosive in pharmaceutical and chemical industries has been posing alarming threats to the environment and public health. The detection of PA in aqueous medium and vapor state is extremely important for military and civilian safety. Here, we report the synthesis of water soluble 1, 8-naphthalimide (ANDI) and multimodal sensing applications of aggregated nano materials for nitro explosives such as picric acid (PA) in aqueous, solid surface and vapor phase. The ANDI nano aggregates demonstrated substantial selectivity and ultrasensitive detection of PA with exceptional quenching constant 7.23×106 M−1 and limit of detection 149 ppb. The quenching takes place due to ground state charge transfer complex formation between PA and ANDI. Equilibrium simulation and the potential of mean force calculations reveal that the ANDI self-assembly is stabilized by extensive π-π interactions and the primary driving force behind the recognition of PA by the assembly is van der Waals interactions. ANDI aggregates would be potential materials for the construction of low cost and light weight nitroaromatic explosive sensors for future application.

Charge-transfer complexes and their applications in optoelectronic devices

After several decades of intense researches on organic optoelectronics, several types of optoelectronic devices such as organic light-emitting devices (OLEDs) have become commercially viable, and performance of organic photovoltaic (OPV) devices has seen significant progress. At the same time, scientists are getting better understanding on the device physics, and the important roles of charge-transfer (CT) states in these devices are widely recognized. CT states are formed upon CT interaction between donor (D) and acceptor (A) molecules. When the extent of CT is high enough, materials with the CT states are specifically referred as charge-transfer complexes (CTCs). Depending on their formation mechanisms, CTCs can be classified into ground-state CTCs (GSCs) and excited-state CTCs (exciplexes). Novel optoelectronic properties of GSCs, including their abnormally high electrical conductivities, long-wavelength photon absorption, charge-generation, etc., have been applied in various optoelectronic devices. On the other hand, attention of excited CTCs is primarily focused on exciplex emission and CT absorption. Recent experimental evidence deepens the understanding of CT states and their new applications are exploited. As there are limited systematic reviews on the application of CTCs in different organic devices, this review intends to fill this gap by giving a brief overview of novel CTC applications and correlating CT properties with device performance.

Fundamental Mechanisms of Lewis Acid Doping of Organic Semiconductors

One key challenge in the field of organic semiconductors (OSCs) and their application in organic electronics is controlling the electronic properties of the OSC by p-/n-doping in a predictable manner. It has been established that upon dopant admixture either integer or fractional charge transfer can occur, where the parameters deciding one over the other are still under debate. In numerous studies integer charge transfer was found for conjugated polymers, while small molecular OSCs show a tendency towards fractional charge transfer forming ground state charge transfer complexes (1). The typical approach to assure integer charge transfer is using molecular dopants with a high electron affinity, exceeding the ionization energy of the OSC (for p-doping), as the dopant then exhibits an empty orbital lying lower in energy than the occupied frontier molecular orbital of the semiconductor. Recently, however, a transition between the two scenarios has been reported for polythiophene and the strong molecular p-dopant F4TCNQ, where aging of the samples appeared to promote the formation of charge-transfer complexes showing fractional charge transfer (2). Another study highlighted the key role of the microstructure for the doping process, where different polymorphs show either fractional or integer charge transfer (3).This lack of predictability of traditional doping employing strong donors/acceptors recently led to intense research efforts to find alternative approaches. There, using Lewis acids (LAs) as molecular p-dopants for OSCs has been found to be particularly promising, as these compounds react selectively with Lewis bases to form robust adducts. This makes LAs, in principle, chemically selective dopants that attack OSCs only at the sites where electron lone pairs are located. Interestingly, despite an electron affinity far below the ionization energy of polythiophene, it has been found that the LA BCF can readily ionize this material, which is incompatible with the conventional picture of integer charge transfer as detailed above (4). Very recently, it has been suggested that LA doping does not follow from the formation of an adduct, but instead, that the LA simply act as a protonating agent after forming a complex with water and, hence, becoming a Br∅nsted acid (5).In this presentation, I will briefly review these ideas and discuss how the concepts of electron affinity, ionization energy, integer, and partial charge transfer as used in the field relate to the doping using LAs. By correlating experimental data from optical and infrared spectroscopy with DFT calculations, I will provide alternative descriptors that allow to clarify the discussion and, more importantly, that have predictive power towards the use of Lewis acids as dopants for OSCs. Finally, I will show that the use of these descriptors, in the case of polythiophene doped with BCF discussed above (4), lift the apparent theoretical inconsistency, and as such, will be of high value for a comprehensive larger-scale exploration of OSCs doping using LAs. 1. Salzmann et al., Acc. Chem. Res. 2016, 49, 3702. Watts et al., Chem. Mater. 2019, 31, 6986−69943. Jacobs et al., Materials Horizons. 2018, 5, 6554. P. Pingel et al., Adv. Electron. Mater. 2016, 2:1600204.5. B. Yurash et al., Nature Materials. 2019, 18, 1327–1334

Formation of Ion Pairs and Charge-Transfer Complexes in the p-Doping of Organic Semiconductors

The formation of ion pairs (IPA) through integer charge transfer and ground-state charge-transfer complexes (CPXs) with only fractional charge transfer are the two known mechanisms in the molecular doping of conjugated polymers and molecules, which form the material class of organic semiconductors (OSCs). As it entails no immediate ionization of the OSC, CPX formation is regarded as detrimental to the doping efficiency. For IPA formation to occur, a match between the electron affinity (EA) of the p-dopant and the ionization energy (IE) of the OSC is expected as crucial, while their pronounced frontier molecular orbital overlap should promote CPX formation instead [1].To explore these complementary scenarios, we first studied the thermal de-doping of the prototypical conjugated polymer poly(3-hexylthiophene) (P3HT), p-doped with the common strong electron acceptor tetrafluoro-tetracyanoquinodimethane (F4TCNQ) [2]. We combined grazing incidence X-ray diffraction (GIXRD) with Fourier-transform infrared spectroscopy (FTIR) to determine the microstructure, and absorbance spectroscopy (UV/vis/NIR) to observe the spectral fingerprint of the two doping scenarios. We found two microstructural environments through their distinguished thermal stabilities, where, the dopants were observed (i) alternatingly stacked with the polymer backbone as well as (ii) dispersed in its sidechain region. From FTIR and UV/vis/NIR we deduce that all dopants are fully ionized, although packing between dopant and polymer backbone would be expected to favor CPX formation instead. Notably, while characteristic shifts of the mid-infrared cyano-stretch modes of TCNQ derivatives are known to well indicate the degree of charge transfer, we show here that they allow further to assess the dopant site in the polymer environment.We further investigated the influence of EA with respect to IE by contrasting F4TCNQ with its derivatives of lower degree of fluorination, which translates into reduced EA while leaving the spatial aspects of the dopant largely intact. We find that using F2TCNQ and FTCNQ still results in IPA formation in spite of EA < IE, which we understand through the lower degree of spatial, and therefore energetic order in OSCs as compared to inorganic semiconductors, which therefore possess no sharp band edges. Surprisingly, at high doping concentrations (additional) CPX formation occurred for all the differently strong dopants, which highlights the complexity of these systems going beyond the sole impact of the energetics of the individual constituents.Finally, we juxtaposed the known tendency of small molecular OSCs to form CPXs and that of polymer OSCs to form IPAs. To maximize the comparability with P3HT, alkylated oligothiophenes of different length were synthesized in-house (from 4 to 10 thiophene repeat units) and doped with F4TCNQ. For the longest oligomer, we were able to observe the switch from the CPX regime into that of IPA, i.e., we approach the doping behavior polymer limit. Knowing this threshold is valuable for applications in organic electronics where vacuum processible small molecular OSCs are preferred over polymeric OSCs, which are only processible via solution-based methods.[1] I. Salzmann, G. Heimel, M. Oehzelt, S. Winkler, N. Koch, Acc. Chem. Res. 2016, 49, 370.[2] H. Hase, K. O’Neill, J. Frisch, A. Opitz, N. Koch, I. Salzmann, The Journal of Physical Chemistry C 2018, 122, 25893.

A selective turn-off fluorescence detection of nitroexplosive 2,4,6-trinitrophenol by pyridinium-based chemosensor in pure aqueous medium

A chemosensor 1-(2-(6-oxobenzo [4,5]imidazo [1,2-c]quinazolin-5(6H)-yl)ethyl)pyridin-1-ium bromide (BZQZPy) bearing benzimidazo-quinazolinone and pyridinium moieties has been developed for the nanomolar detection of 2,4,6-trinitrophenol (TNP) in aqueous medium. BZQZPy exhibited excellent cyan blue fluorescence that is quenched on the addition of TNP via turn-off fluorescence response. The UV–visible, fluorescence and 1H NMR spectroscopy, lifetime measurements and theoretical calculations suggested that ground state charge transfer complex formation and energy transfer mechanisms are possible causes for this fluorescence quenching. BZQZPy is highly sensitive and selective towards TNP with high quenching constant (Ksv) of 1.53 × 104 M−1 and low detection limit of 20 nM. The proposed chemosensor is also applicable for the on-site determination of TNP on filter paper and in real water samples.

Novel 2‐Arylbenzothiazoles: Selective Chromogenic and Fluorescent Probes for the Detection of Picric Acid

AbstractA series of 2‐arylbenzothiazoles has been designed and synthesized as chromogenic and fluorescent probes for the detection of picric acid (PA) over other nitro analytes. A straightforward condensation of a variety of aryl nitriles with 2‐aminobenzenethiol under metal‐ and base‐free conditions afforded the corresponding products in 26–98% yields. All 2‐arylbenzothiazoles could efficiently sense PA at micromolar levels. The highly sensitive compound 2‐(4‐((2‐methyl‐1H‐imidazol‐1‐yl)methyl)phenyl)benzo[d]thiazole (3c) showed 95% fluorescence quenching on addition of 1.0 eq of PA which can be attributed to hydrogen bonding and ground state charge transfer complex formation with a detection limit of 19.0 μM. The high sensitivity of 3 c for PA detection was also established by test strips experiment. The sensing mechanism was explored by 1H NMR titrations and Job's plot.

Ground state charge transfer complex formation of some metalloporphyrins with aromatic solvents: Further theoretical and experimental investigations

In our earlier work (Chem. Phys. Letts. 592 (2014) 149–154), a new broad band was observed in the near infrared region (700–900nm) of the steady state absorption spectra of some metalloporphyrins (zinc tetraphenylporphyrin, zinc octaethylporphyrin and magnesium octaethylporphyrin) in aromatic solvents (chlorobenzene, 1,2-dichlorobenzene, benzonitrile, benzene and toluene) at high concentrations (~10−4molL−1). The band was ascribed to be due to ground state charge transfer complexation between solute and solvent molecules. In the present work, density functional theory calculations are carried out to study the possibility of such ground state charge transfer complex formation between zinc tetraphenylporphyrin and four aromatic solvents viz., benzene, toluene, chlorobenzene and benzonitrile with 1:1 and 2:1 solvent-solute stoichiometries. Also, we determined the association constants for the ground state charge transfer complex formation of zinc tetraphenylporphyrin and zinc octaethylporphyrin with two aromatic solvents (benzene and benzonitrile) by Benesi–Hildebrand method.

Building Block Dependent Morphology Modulation of Cage Nanoparticles and Recognition of Nitroaromatics.

Morphology of nanomaterials has a strong impact on their chemical/physical properties, and controlled synthesis of such materials with desirable morphology is a major challenge. This article presents the role of a building block in the morphology of organic cage particles. In this context, three organic cages (A3 X2 , B3 X2 , and C3 X2 ) were devised from triphenylamine-based dialdehydes (A-C) and a flexible triamine (X) by utilizing dynamic imine chemistry. All of the synthesized cages were characterized by various spectroscopic techniques, which suggested the formation of [3+2] assembled architectures. Though the cages are isostructural, structural variation in the aldehyde building blocks imparted by the incorporation of phenyl moieties into the triphenylamine core produces morphologically diverse cage particles, as indicated by SEM. The synthesized cages were found to be fluorescent; the reduced analogue of cage A3 X2 (A3 X2r ) was tested to explore its use as a chemosensor for the detection of nitroaromatic explosives. The experimental findings suggest high selectivity and sensitivity of A3 X2r towards picric acid (PA) among the various nitroaromatics tested. A theoretical investigation of fluorescence quenching suggested that formation of a ground-state charge-transfer complex with a resonance energy-transfer (RET) process could be the main reason behind such selectivity of the cage towards PA.

Molecular Electrical Doping of Organic Semiconductors: Fundamental Mechanisms and Emerging Dopant Design Rules.

Today's information society depends on our ability to controllably dope inorganic semiconductors, such as silicon, thereby tuning their electrical properties to application-specific demands. For optoelectronic devices, organic semiconductors, that is, conjugated polymers and molecules, have emerged as superior alternative owing to the ease of tuning their optical gap through chemical variability and their potential for low-cost, large-area processing on flexible substrates. There, the potential of molecular electrical doping for improving the performance of, for example, organic light-emitting devices or organic solar cells has only recently been established. The doping efficiency, however, remains conspicuously low, highlighting the fact that the underlying mechanisms of molecular doping in organic semiconductors are only little understood compared with their inorganic counterparts. Here, we review the broad range of phenomena observed upon molecularly doping organic semiconductors and identify two distinctly different scenarios: the pairwise formation of both organic semiconductor and dopant ions on one hand and the emergence of ground state charge transfer complexes between organic semiconductor and dopant through supramolecular hybridization of their respective frontier molecular orbitals on the other hand. Evidence for the occurrence of these two scenarios is subsequently discussed on the basis of the characteristic and strikingly different signatures of the individual species involved in the respective doping processes in a variety of spectroscopic techniques. The critical importance of a statistical view of doping, rather than a bimolecular picture, is then highlighted by employing numerical simulations, which reveal one of the main differences between inorganic and organic semiconductors to be their respective density of electronic states and the doping induced changes thereof. Engineering the density of states of doped organic semiconductors, the Fermi-Dirac occupation of which ultimately determines the doping efficiency, thus emerges as key challenge. As a first step, the formation of charge transfer complexes is identified as being detrimental to the doping efficiency, which suggests sterically shielding the functional core of dopant molecules as an additional design rule to complement the requirement of low ionization energies or high electron affinities in efficient n-type or p-type dopants, respectively. In an extended outlook, we finally argue that, to fully meet this challenge, an improved understanding is required of just how the admixture of dopant molecules to organic semiconductors does affect the density of states: compared with their inorganic counterparts, traps for charge carriers are omnipresent in organic semiconductors due to structural and chemical imperfections, and Coulomb attraction between ionized dopants and free charge carriers is typically stronger in organic semiconductors owing to their lower dielectric constant. Nevertheless, encouraging progress is being made toward developing a unifying picture that captures the entire range of doping induced phenomena, from ion-pair to complex formation, in both conjugated polymers and molecules. Once completed, such a picture will provide viable guidelines for synthetic and supramolecular chemistry that will enable further technological advances in organic and hybrid organic/inorganic devices.

Highly sensitive fluorescent imidazolium-based sensors for nanomolar detection of explosive picric acid in aqueous medium

Two novel fluorescent coumaryl linked imidazolium salts have been synthesized, characterized and found to be highly selective for nanomolar detection of commonly used explosive picric acid, over other aromatic explosives in aqueous medium. The compounds are highly photostable and are practically applicable for sensing picric acid in real environmental samples, in presence of interfering aromatic/non-aromatic explosives and metal ions. In solution, the high sensitivity of the sensors toward picric acid can be predominantly attributed to the ground-state charge-transfer complex formation based on UV–vis studies, time resolved fluorescence results and DFT calculations.

Donor-Acceptor Heterojunction Configurations Based on DNA-Multichromophore Arrays.

Multichromophore arrays of bis(2-thienyl)diketopyrrolopyrrole (DPP) and naphthalenediimide (NDI) with two Zn(II) -cyclens were constructed using thymidine DNA as a scaffold through the binding of the Zn(II) -cyclens with thymine bases. We demonstrate photocurrent generation in a donor-acceptor heterojunction configuration consisting of the DPP (donor) and NDI (acceptor) arrays co-immobilized on an Au electrode. The co-immobilized electrode exhibited good photocurrent responses because of the efficient charge separation between the DPP and NDI arrays. In contrast, an immobilized electrode consisting of randomly assembled DPP-NDI arrays generated no photocurrent response because DPP formed ground-state charge-transfer complexes with NDI in the randomly assembled arrays. Therefore, our approach to generate donor-acceptor heterojunctions based on DNA-multichromophore arrays is a useful method to efficiently generate photocurrent.

Electron-rich triphenylamine-based sensors for picric acid detection.

This paper demonstrates the role of solvent in selectivity and sensitivity of a series of electron-rich compounds for the detection of trace amounts of picric acid. Two new electron-rich fluorescent esters (6, 7) containing a triphenylamine backbone as well as their analogous carboxylic acids (8, 9) have been synthesized and characterized. Fluorescent triphenylamine coupled with an ethynyl moiety constitutes π-electron-rich selective and sensitive probes for electron-deficient picric acid (PA). In solution, the high sensitivity of all the sensors toward PA can be attributed to a combined effect of the ground-state charge-transfer complex formation and resonance energy transfer between the sensor and analyte. The acids 8 and 9 also showed enhanced sensitivity for nitroaromatics in the solid state, and their enhanced sensitivity could be attributed to exciton migration due to close proximity of the neighboring acid molecules, as evident from the X-ray diffraction study. The compounds were found to be quite sensitive for the detection of trace amount of nitroaromatics in solution, solid, and contact mode.

The effect of intercalated behavior in polymer/fullerene blend on the performance of organic bulk heterojunction solar cells

The morphology of active layer in organic bulk heterojunction solar cells has important influence on device performance. The intercalated behavior can exist when polymer/small molecular blend system meets the two criteria: the size of the small molecules is smaller than the distance between adjacent side-chains of polymer, and the small molecules should form a ground-state charge-transfer complex with polymer. The intercalated behavior affects the film morphology and is not beneficial to energy conversion process. In this paper, the forming process of intercalation in blend system was introduced. Then we concluded the influence of intercalation on film morphology including crystallization, phase separation and device performance including exciton diffusion, exciton dissociation, and carrier transport. The chemical and physical methods to inhibit intercalated behavior were also recommended at the same time. Furthermore, we posed the critical problems to be resolved in this field and prospect its developing foreground.