Design of a novel class of two-component, highly emissive, low molecular weight supergelator is reported.

An unsymmetrical squaraine (SQ) derivative containing anthracene and phenyl hydrazine (ANPHSQ) units linked to the central SQ was synthesized and used as electron donors in bulk heterojunction photovoltaic mode organic photodetectors (OPD), containing PCBM as the electron acceptor. Although the ANPHSQ exhibited a strong narrow band in the near infrared peaking at similar to 760 nm in solution, the OPD constructed with this dye exhibited a broad spectral response extending to 950 nm. The enhanced sensitivity in the long wavelength region could be attributed to formation of ANPHSQ aggregates within the devices. A photocurrent of 1.3 mA/cm(2), almost 3-5 orders of magnitude larger than the dark current (similar to 50 nA/cm(2)), was observed in the presence of light at -1 V bias condition. Devices showed an increase in external quantum efficiency from similar to 4 to similar to 12% as the bias varied from 0 to -1 V. At a reverse bias of -1 V, the device with a ANPHSQ exhibited a maximum shot-noise-limited specific detectivity of 6 x 10(11) cm Hz1/2 W-1 (Jones) @ 840 nm with an ultrafast photoresponse in the range of similar to 15 ns. The study of relaxation dynamics of the ANPHSQ excited state using femtosecond pump-probe spectroscopy and time-correlated single-photon counting indicated efficient charge transfer between the excited state of ANPHSQ and PCBM.

Controlled self-organization of organic semiconductor molecules into specifically desired architectures on substrates of interest is one of the most imperative challenges faced in the fabrication of high-performance organic electronic devices. Herein, we report the self-organization of a star-shaped molecule FDT-8 into a highly favored structure, namely, a vertical stack. Thermal annealing of films of FDT-8 deposited on PEDOT: PSS coated ITO substrates was observed to assist the organization of the molecules into columnar stacks. A significant enhancement in the hole (≈50-fold) and the electron (≈13-fold) carrier mobility was observed in single-carrier devices upon thermal annealing that could be attributed to the aforementioned self-organization. The ability of these molecules to spontaneously self-organize was utilized to fabricate bilayer light-emitting devices.

Ultrafast charge carrier dynamics as well as the generation of polaron pair in squaraine (SQ) and squaraine:[6,6]-phenyl-C 71-butyric acid methyl ester (SQ:PCBM71) have been studied using ultrafast transient absorption spectroscopy (UTAS). The current study reveals that the pure SQ exhibits the creation of singlet and triplet states; however, incorporation of PCBM71 in SQ results in the formation of polaron pairs with ∼550ps lifetime, which in turn leads to the creation of free electrons in the device. We show that the considerable increment in monomolecular and bimolecular recombination in SQ:PCBM71 compared to pure SQ which describes the interfacial compatibility of SQ and PCBMC71 molecules. The present work not only provides the information about the carrier generation in SQ and SQ:PCBM71 but also gives the facts relating to the effect of PCBM71 mixing into the SQ which is very significant because the SQ has donor-acceptor-donor (D-A-D) structure and mixing one more acceptor can introduce more complex recombinations in the blend. These findings have been complimented by the charge transport study in the device using impedance spectroscopy. The various important transport parameters are transit time (τt), diffusion constant (Dn), global mobility (μ) and carrier lifetime (τr). The values of these parameters are 26.38 μs, 4.64x10-6 cm2s-1, 6.12x10-6 cm2V-1s-1 and 399 μs, respectively. To the best of our knowledge such study related to SQ is not present in the literature comprehensively.

BACKGROUND:Photodynamic therapy (PDT) has clinical approval for use as a minimally invasive therapeutic procedure that is able to exert selective cytotoxic activity toward malignant cells. The dye selected for our study, symmetrical diiodinated squaraine, is one of the newly developed photosensitizers. The study is designed to determine the efficacy of PDT mediated by symmetrical diiodinated squaraine in skin tumor induced Swiss albino mice.METHODS:Skin tumor was induced in mice with dimethyl benzanthracene (DMBA) and croton oil. After squaraine administration to the tumor mice, photodynamic treatment of tumors was performed using a 1000W halogen lamp corresponding to the light dose of 100J/cm2. The mice were euthanized and skin flaps and tumor tissues from the back of mice were excised for biochemical studies. The biochemical parameters analyzed include some relevant tumor markers for epithelial tissues, inflammatory markers and markers of apoptosis. The gene expression studies were done by RT-PCR.RESULTS:After two weeks of the treatment, there was significant inflammation. However at 90days after PDT, the parameters reverted to near-normal values. All marker parameters of tumor progression brought back to normal levels by PDT. Increased caspase-3 activity in PDT treated group shows that cell death might have occurred by apoptosis. The gene expression profile confirms the results.CONCLUSIONS:The results of the whole study show the therapeutic efficacy and apoptosis mediated tumor destruction by squaraine PDT.

Herein, we report the synthesis, self-assembly, and electroluminescence characteristics of a new green-emitting, pseudodiscoid chiral molecule, OXDC, containing an electron-donating stilbene core and an electron-accepting oxadiazole substituent. The helical organization and specific interaction of the chiral pseudodiscoid molecule resulted in the formation of self-assembled nanofibers with a columnar superstructure. Macroscopic chirality was observed in both the liquid-crystalline phases and the self-assembled nanofibers of OXDC, a feature which was absent in the analogous achiral oxadiazole derivative reported earlier [ Sivadas , A. P. ; Supergelation via Purely Aromatic π-π Driven Self-Assembly of Pseudodiscotic Oxadiazole Mesogens . J. Am. Chem. Soc. 2014 , 136 , 5416 - 5423 ]. A high-performance organic light-emitting device was demonstrated using OXDC as the emitting material, with a luminous intensity of 10 115 cd m-2 at 5 V and chromaticity coordinates of (0.32, 0.51).

Novel glycoconjugated squaraine dyes were synthesized, which exhibited excellent internalization in tumor cells and are potent fluorogenic imaging probes for tumor selective optical imaging.

The synthesis, self-assembly and mechanochromic properties of a series of oxadiazole derivatives (TFOXD1, TFOXD4, TFOXD6 and TFOXD8) substituted with a dialkoxy stilbene and trifluoromethyl benzene moieties are reported. All the derivatives formed stable gels in aliphatic solvents and with the exception of TFOXD1 exhibited monotropic liquid crystalline behavior. The photophysical properties of their films and gels were dependent on the length of their alkoxy substituent, with the formation of excimers being observed in the derivatives containing longer alkoxy chains. TFOXD4 and TFOXD6 exhibited reversible mechanochromic luminescence switching. XRD studies confirmed the reversible phase transformation between crystalline and amorphous forms.

The energy transfer efficiencies of organic inorganic nanohybrids comprised of two structurally similar squaraine dyes and CdSe nanoparticles were studied in detail and compared. Carbazole based unsymmetrical squaraine dyes (CTSQ-1 and CTSQ-2) having modified absorption characteristics were considered for modulating the effect of the overlap integral on energy transfer rate with the designed QDs. CTSQ-2 with similar to 1.75 times higher molar extinction coefficient and 35 nm red-shift in absorption resulted in an similar to 2.4 times faster energy transfer rate with QD. The calculated energy transfer rates (k(T) = 1.35 X 10(8) s(-1) and 3.26 X 10(8) s(-1) respectively for QD:CTSQ-1 and QD:CTSQ-2 nanohybrids) are at least one order of magnitude higher than both radiative (k(r) = 5.97 X 10(6) s(-1)) and nonradiative decay rate constants (k(nr) = 1.89 X 10(7) s(-1)) of QDs yielding very high FRET efficiency. The Stern-Volmer analysis of the quenching data indicated mainly static interaction of dyes with the QDs thus suggesting formation of organic-inorganic nanohybrids. When incorporated in dye-sensitized solar cells, the nanohybrids with 93% FRET efficiency, exhibited an overall 43% improvement in the photovoltaic performance. Among the two architectures employed for device fabrication the one with the smallest donor-acceptor distance delivered the best performance. Due to increased contribution from QDs, the IPCE spectra clearly indicate panchromatic response from the visible to NIR region. Thus, photovoltaic performance of NIR absorbing dyes were successfully improved by constructing panchromatic organic-inorganic nanohybrid materials.

Interaction of light with electron donor-acceptor π-conjugated systems leading to intramolecular charge transfer (ICT) plays an essential role in transformation of light energy. Here the cascade of photoinduced ICT processes is directly observed by investigating the excited state relaxation dynamics of cyano and mono/di methoxy substituted diphenyl acetylene derivatives using femtosecond pump-probe spectroscopy and nanosecond laser flash photolysis. The femtosecond transient absorption spectra of the chromophores upon ultrafast excitation reveal the dynamics of intermediates involved in transition from initially populated Frank-Condon state to local excited state (LE). It also provides the dynamic details of the transition from the LE to the charge transfer state yielding the formation of the radical ions. Finally, the charge transfer state decays to the triplet state by geminate charge recombination. The latter dynamics are observed in the nanosecond transient absorption spectra. It is found that excited state relaxation pathways are controlled by different stages of solvation and intramolecular relaxation depending on the solvent polarity. The twisted ICT state is more stabilized (978 ps) in acetonitrile than cyclohexane where major components of transient absorption originate from the S1 state.

Atom transfer radical polymerization is utilized to synthesize an amphiphilic photoresponsive triblock copolymer poly(trifluorostilbene methacrylate)‐b‐polystyrene‐b‐polyethylene oxide (PTFS‐b‐PSt‐b‐PEO). Adding water into tetrahydrofuran solution of PTFS‐b‐PSt‐b‐PEO results in the formation of spherical vesicular aggregates brought about as a result of the association of the water insoluble TFS and St blocks. UV irradiation of the colloidal solution causes trans–cis isomerization of the TFS units which result in morphological transition of the spherical vesicular aggregates to rod‐like particles. This morphological transition is studied using dynamic light scattering, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and UV–vis and fluorescence spectroscopy. The trans‐stilbene units have almost zero dipole moment whereas the corresponding cis‐form has a definite dipole moment. This polarity difference associated with structural change is expected to be the main reason for the structural transformation of the aggregates. It is also found that PTFS‐b‐PSt‐b‐PEO aggregates have the ability of trapping organic dyes inside their hydrophobic cavity thereby making them water soluble. Subsequently the encapsulated dye can be partially released upon UV irradiation. image

Unsymmetrical squaraine dyes (CTSQ-1 and CTSQ-2) with carbazole thiophene donor units were synthesized, characterized and used as sensitizers in dye-sensitized solar cells (DSSCs). These squaraines exhibited intense absorption in the near IR-visible region of the solar spectrum both in solution and on TiO2 surface. The LUMO level of the parent sensitizer (CTSQ-2) was positioned at a potential much close to the conduction band of TiO2 resulting in lack of enough driving force for electron injection which was modulated by structurally changing the donor carbazole moiety (CTSQ-1), pushing the LUMO more positive thereby enhancing the driving force. Theoretical calculations were carried out in order to have a better understanding of the electron density distribution in CTSQ-1 and CTSQ-2. Electron injection dynamics in CTSQ-1 was studied in detail by changing the Li(+) concentration and its effects on photovoltaic parameters were discussed with the help of JV, IPCE, lifetime and EIS measurements.

Detailed photophysical properties of cyano and mono (MA)/bis alkoxy (DA) substituted diphenylacetylene moieties with different alkyl chain lengths (methyl (1), octyl (8) and dodecyl (12)) were investigated in solution and the solid state in an effort to determine the effect of self-aggregation on these properties. The solvated molecules showed a minimal bathochromic shift with an increase of solvent polarity in their absorption spectra, whereas a significant shift was observed in the emission spectra. This could be attributed to the relatively low change in dipole moment between ground and Franck-Condon excited states and luminescence arising from the intramolecular charge transfer state with a dipole moment significantly higher than that of the ground state. In solid state the emission quantum yields of these materials were significantly higher than in solution. For DA1, polymorphic materials with distinct photophysical properties were obtained. The DA1 materials obtained by fast precipitation (DA1) showed broad fluorescence with peaks at 398, 467 and 535 nm upon excitation at different wavelengths. Detailed analysis of absorption, emission and excitation spectra and lifetime experiments indicated that these peaks could be attributed to the monomer, J-and H-type aggregates respectively. Whereas the crystals obtained by slow crystallization (DA1C) showed only one emission peak at around 396 nm attributed to the monomer. This is supported by the single crystal X-ray structure which consists of a monomer molecule having minimal interaction with nearest neighbour molecules.

The use of a new block copolymer made up of poly(azobenzene methacrylate) (PMAzo) and poly(3‐O‐4‐vinylbenzoyl‐d‐glucopyranose) (PBG) is described for the solubilization of water‐insoluble dyes such as Nile Red in aqueous solutions. This polymer, which is abbreviated as PMAzo‐b‐PBG, self‐assembles into spherical aggregates in water as confirmed by atomic force microscopy. UV irradiation of the aqueous polymer solution destabilizes the aggregates brought about as a result of the trans–cis isomerization of the MAzo units. Dissociated aggregates reunite to form tubular aggregates when the solution is irradiated with 450 nm light. Nile Red, which is a hydrophobic dye, can be incorporated into these aggregates and subsequently released using UV light. The encapsulation, release, and re‐encapsulation of Nile Red are studied using fluorescence spectroscopy. image

A series of highly luminescent oxadiazole-based stilbene molecules (OXD4, OXD8, OXD10, and OXD12) exhibiting interesting enantiotropic liquid crystalline and gelation properties have been synthesized and characterized. The molecules possessing longer alkyl substituents, OXD10 and OXD12, possess a pseudodisc shape and are capable of behaving as supergelators in nonpolar solvents, forming self-standing gels with very high thermal and mechanical stability. Notably the self-assembly of these molecules, which do not possess any hydrogen-bonding motifs normally observed in most reported supergelators, is driven purely by π-stacking interactions of the constituent molecules. The d-spacing ratios estimated from XRD analysis of OXD derivatives possessing longer alkyl chains show that the molecules are arranged in a columnar fashion in the mesogens and the self-assembled nanofibers formed in the gelation process.

The synthesis and self-assembling properties of C-3 symmetric donor-acceptor molecules containing 1,3,4-oxadiazole and bisthiophene moieties in the core functionalized with octyl (BTOX8) and dodecyl (BTOX12) substituted phenyl acetylene units at the periphery are reported. BTOX8 was found to form gels only in aliphatic solvents, whereas BTOX12 formed gels in both aliphatic and aromatic solvents. Photophysical analysis of BTOX12 solutions showed a striking effect of the solvent on the nature of the self-assembled aggregate formed. Our studies indicate that in aliphatic solvents such as n-decane the solvent molecules interact mainly with the alkyl regions of BTOX12. As a result the pi-pi interaction between the neighbouring molecules becomes feasible resulting in strong excitonic coupling between the neighbouring molecules leading to excimer type emission. In aromatic solvents the solvent molecules interact mainly with the chromophoric part of BTOX12 resulting in reduced pi-stacking between the molecules in the aggregate leading to monomer type emission. Films prepared from aliphatic and aromatic solvents exhibited photophysical properties significantly similar to those observed in the respective solvents. Photophysical studies of the films indicated that the films prepared from n-decane exhibited an H-type molecular arrangement whereas the films prepared from toluene exhibited a slipped stack J-type arrangement.

Here, we report the synthesis, photophysical properties and photodynamic effects in DLA live cells of three water soluble squaraine dyes, viz. bisbenzothiazolium squaraine dyes SQMI and SQDI with iodine in one and both benzothiazolium units, respectively, and an unsymmetrical squaraine dye ASQI containing iodinated benzothiazolium and aniline substituents. The diiodinated SQDI showed an anomalous trend in both fluorescence and triplet quantum yields over the monoiodinated SQMI, with SQDI showing higher fluorescence and lower triplet quantum yields compared to SQMI. Nanosecond laser flash photolysis of SQDI and SQMI indicated the formation of triplet excited states with quantum yield of 0.19 and 0.26, respectively. On photoirradiation, both the SQDI and SQMI generate singlet oxygen and it was observed that both dyes undergoing oxidation reactions with the singlet oxygen generated. ASQI which exhibited a lower triplet quantum yield of 0.06 was, however, stable and did not react with the singlet oxygen generated. In vitro cytotoxicity studies of these dyes in DLA live cells were performed using Trypan blue dye exclusion method and it reflect an order of cytotoxicity of SQDI>SQMI>ASQI. Intracellular generation of the ROS was confirmed by dichlorofluorescein assay after the in vitro PDT.

Photodynamic therapy (PDT) is emerging as a promising non-invasive treatment for cancers. It involves three key components; a photosensitizer, light and tissue oxygen. Even though several photosensitizers have been investigated for their use in PDT, they have several disadvantages and hence the search for more effective sensitizers has become important in recent years. The dye selected in our study - symmetrical diiodinated benzothiazolium squaraine (SQDI) - is one of the newly developed photosensitizers. The study aimed to evaluate the in vitro cytotoxicity of the dye on Ehrlich's Ascites Carcinoma (EAC) cells and to assess the in vivo toxicity on Swiss Albino mice. The EAC cells were maintained in the peritoneum of mice and used to study the dark toxicity and phototoxicity by Trypan blue dye exclusion method, estimation of Reactive Oxygen Species (ROS), caspase activity and levels of thiobarbituric acid reactive substances (TBARS). The in vitro studies revealed that the dye induces toxicity in the presence of light and mediates cell death. The in vivo part of the study, which dealt with the toxicity evaluation in the body of Swiss Albino mice, was done by analyzing the parameters like serum glutamate oxaloacetate transaminase (SGOT), serum glutamate pyruvate transaminase (SGPT), lactate dehydrogenase (LDH), creatine kinase (CK) and alkaline phosphatase (ALP). No significant change was observed in the above mentioned parameters in the dye administered group when compared to control. Altogether, this experiment indicates that the SQDI selected for our study may be used as an efficient photosensitizer for PDT applications and does not elicit acute toxicity to normal tissues in the absence of light.