Inspired by the powerful photosensitizing properties of the red hair pigments pheomelanins, a photoresponsive cysteine-containing variant of the adhesive biopolymer polydopamine (pDA) is developed via oxidative copolymerization of dopamine (DA) and 5-S-cysteinyldopamine (CDA) in variable ratios.Chemical and spectral analysis indicate the presence of benzothiazole/benzothiazine units akin to those of pheomelanins. p(DA/CDA) copolymers displayimpedance properties similar to those of biological materials and a marked photoimpedance response to light stimuli. The use of the p(DA/CDA) copolymerto implement a solution-processed hybrid photocapacitive/resistive metalinsulator- semiconductor (MIS) device disclosed herein is the fi rst example oftechnological exploitation of photoactive, red-hair-inspired biomaterials as soft enhancement layer for silicon in an optoelectronic device. The bio-inspiredmaterials described herein may provide the active component of new hybrid photocapacitive sensors with a chemically tunable response to visible light.

A white emitting copolymer with the polyphenylenevinylene (PPV) structure is obtained via the Stille cross-coupling reaction. Substitution of hydrogen atoms with fluorine atoms on the vinylene units of poly(1,4-dialkoxyphenylenevinylene) shifts the emission from orange-red to blue. White emission isobtained by combining dialkoxyphenylenedifluorovinylene and dialkoxyphenylenevinylene units in proper ratio. The two complementary emitters are obtained separately by Stille polymerization reaction. Then, the two reaction mixtures are combined without purification in different ratios and further reactedin similar experimental conditions. A white luminescent material is obtained using 99/1 mixing ratio. OLED devices fabricated with this copolymer shows near-white emission with CIE (0.30, 0.40) and excellent stability in the range 10e200 cd/m2.

N-functionalization of 5,6-dihydroxyindole with a hydrophilic triethyleneglycol (TEG) chain provides access to a new class of water-soluble eumelanin-like materials with relatively high dielectric constant and polyelectrolyte behaviour, reflecting enhanced charge transport by in-depth incorporation of hydration networks.

The use of an amphiphilic aryleneethynylene fluorophore as a plasma membrane marker in fixed and livingmammalian cells and liposome model systems is demonstrated. We show here that the optical properties ofthe novel dye are almost independent on pH, in the range 5.0-8.0. Spectroscopic characterization performedon unilamellar liposomes ascertained that the fluorescence intensity of the aryleneethynylene fluorophoregreatly increases after incorporation in lipidic membranes. Experiments performed on different mammaliancells demonstrated that the novel membrane marker exhibits fast staining and a good photostability thatmake it a suitable tool for live cell imaging. Importantly, the aryleneethynylene fluorophore was alsoshown to be a fast and reliable blue membrane marker in classical multicolor immunofluorescence experiments.This study adds new important findings to the recent exploitation of the wide class ofaryleneethynylene molecules as luminescent markers for biological investigations.

A systematic computational investigation on the optical properties of a group of novel benzofulvene derivatives (Martinelli 2014 Org. Lett. 16 3424-7), proposed as possible donor materials in small molecule organic photovoltaic (smOPV) devices, is presented. A benchmark evaluation against experimental results on the accuracy of different exchange and correlation functionals and semi-empirical methods in predicting both reliable ground state equilibrium geometries and electronic absorption spectra is carried out. The benchmark of the geometry optimization level indicated that the best agreement with x-ray data is achieved by using the B3LYP functional. Concerning the optical gap prediction, we found that, among the employed functionals, MPW1K provides the most accurate excitation energies over the entire set of benzofulvenes. Similarly reliable results were also obtained for range-separated hybrid functionals (CAM-B3LYP and wB97XD) and for global hybrid methods incorporating a large amount of non-local exchange (M06-2X and M06-HF). Density functional theory (DFT) hybrids with a moderate (about 20-30%) extent of Hartree-Fock exchange (HFexc) (PBE0, B3LYP and M06) were also found to deliver HOMO-LUMO energy gaps which compare well with the experimental absorption maxima, thus representing a valuable alternative for a prompt and predictive estimation of the optical gap. The possibility of using completely semi-empirical approaches (AM1/ZINDO) is also discussed.

Three new metal-free organic dyes with the [1]benzothieno[3,2-b]benzothiophene (BTBT) ?-bridge, having thestructure donor-?-acceptor (D-?-A) and labeled as 19, 20 and 21, have been designed and synthesized for application in dyesensitizedsolar cells (DSSC). Once the design of the ?-acceptor block was fixed, containing the BTBT as the ?-bridge and thecyanoacrylic group as the electron acceptor and anchoring unit, we selected three donor units with different electron-donorcapacity, in order to assemble new chromophores with high molar extinction coefficients (?), whose absorption features wellreflect the good performance of the final DSSC devices. Starting with the 19 dye, which shows a molar extinction coefficient ? ofover 14,000 M-1 cm-1 and takes into account the absorption maximun at the longer wavelength, the substitution of the BFTdonor unit with the BFA yields a great enhancement of absorptivity (molar extinction coefficient ? > 42,000 M-1 cm-1), untilreaching the higher value (? > 69,000 M-1 cm-1) with the BFPhz donor unit. The good general photovoltaic performancesobtained with the three dyes highlight the suitable properties of electron-transport of the BTBT as the ?-bridge in organicchromophore for DSSC, making this very cheap and easy to synthesize molecule particularly attractive for efficient and low-costphotovoltaic devices

Three fluorenone-derived two-photon fluorescent probes (TK) targeting the lysosomes (TK-Lyso) and mitochondria (TK-Mito1 and TK-Mito2) were synthesized by introducing different diphenylamine moieties into the fluorenone core. The TK dyes showed high biocompatibility and long-term retention, low cytotoxicity, large Stokes shift and good fluorescence quantum yield. The results of the present work disclose a class of organic dyes with potential wide applications as specific and efficient probes for lysosomes and mitochondria in the study of various biological processes.

Conjugated polymers with strongly twisted backbones, such as MEHPPV with fluorinated vinylene units(F-MEHPPV), demand a redefinition of the all-important 'effective conjugation length' ECL, which weextract here by a facile graphical method. In MEHPPV (being essentially planar), the ECL coincideswith the 'maximum conducive chain length' MCC and extends over about n E 9 repetition units (RU). InF-MEHPPV, the MCC is similarly long with n E 8, but the ECL localizes on just one RU. The strong twistin F-MEHPPV persists in the excited state, broadening the emission spectrum and quenching thefluorescence with reduced radiative and enhanced non-radiative rates

A series of push-pull organic dyes based on the cyanoacrylic acid as the acceptor/anchoring group, a dibenzofulvene (DBF) connected with thienyl rings as the ?-bridge, and donor units linked to different positions of the DBF molecule were synthetized and studied. The effects of the donor position on optical and photovoltaic properties were investigated through photophysics, electrochemical and photovoltaic measurements. The results uphold photovoltaic performances largely depend on the electronic structure of the dyes with a synergistic interaction between donor and acceptor groups. In detail, a fine tuning of the photophysical properties can be reached simply selecting the position of the donor unit on the DBF molecule. In particular, the dyes bearing the donor unit on the 3,6-positions of the DBF show better performances in term of light absorption and cell efficiency with respect to the dyes with the donor unit on the 2,7-positions.

Eumelanin-type biopolymers have attracted growing interest in the quest for soft bioinspired functional materials for application in organoelectronics. Recently, a metal-insulator-semiconductor device with a good quality interface was produced by spin coating of a commercial synthetic eumelanin-like material on a dry plasma-modified silicon surface. As a proof-of-concept step toward the design and implementation of next-generation eumelanin-inspired devices, we report herein an expedient chemical strategy to bestow n-type performance to polydopamine, a highly popular eumelanin-related biopolymer with intrinsic semiconductor behaviour, and to tune its electrical properties. The strategy relies on aerial co-oxidation of dopamine with suitable aromatic amines, e.g. 3-aminotyrosine or p- phenylenediamine, leading to good quality black polymeric films. Capacitance-voltage experiments on poly(dopamine/3-aminotyrosine) and poly(dopamine/p-phenylenediamine)-based metal insulator semiconductor devices on p-Si indicated a significant increase in flat band voltage with respect to polydopamine and previous synthetic eumelanin-based diodes. Variations of the flat band voltage under vacuum were observed for each device. These results point to polydopamine as a versatile eumelanin-type water-dependent semiconductor platform amenable to fine tuning of its electronic properties through incorporation of p-conjugating aromatic amines to tailor functionality.

This review is an overview of our previous work on the synthesis and propertiesof poly(p-phenylenevinylene)s (PPVs) selectively fluorinated in different positions of theconjugated backbone. Both the synthetic challenges and the effects of functionalization withfluorine atoms on the optical behavior are discussed, highlighting the peculiarities and theinterest of this class of conjugated polymers. A general polymerization protocol for PPVs,that is based on the Pd-catalyzed Stille cross-coupling reaction of bis-stannylated vinylenemonomers with aromatic bis-halides, has been successfully extended to the synthesis ofselectively fluorinated poly(p-phenylenevinylene)s. The properties of a series of these PPVsdiffering in the number and positions of the fluorine atoms on the conjugated backbone havebeen studied, even in comparison with the non-fluorinated counterparts. The intriguingoptical features of the resulting materials are discussed considering not only the role of theelectronic and steric effects induced by the fluorine substituents, but also the impact of thefluorination on the solid state organization and intermolecular interactions.

A low band-gap copolymer PDTBTFV alternating bis-thienyl-(bis-alkoxy)-benzothiadiazole blocks with difluorovinylene units and its non-fluorinated counterpart PDTBTV have been synthesized and characterized as donor materials in bulk heterojunction (BHJ) solar cells with PCBM as the acceptor. The solar cells with the fluorinated polymer show better photovoltaic performances than those recorded with the non-fluorinated material. Comparative spectroscopic and computational studies, together with morphological, electrical and optical characterization of thin films, have been carried out to shed light on the reasons for the improvement of performances as induced by the double bond fluorination. Our study introduces the fluorinated double bond as a new conjugated unit in donor polymers for BHJ solar cells.

Over the past decade synthetic melanins, melanin-like polymers and melanin-based copolymers have been the focus of growing attention as soft biocompatible functional materials for engineering high performance, low cost optoelectronic devices, such as memory devices, light emitting diodes and field effect transistors. The unique combination of physicochemical properties of melanins, such as broad band absorption in the UV-visible range, intrinsic free radical character, water-dependent hybrid ionic-electronic conductor behaviour and excellent biocompatibility, have inspired use of melanic polymers as valuable functional materials for organic bioelectronics. However, several gaps and issues still hinder rapid progress of melanin-based organic electronics and bioelectronics, including in particular the limited contribution of electronic conductivity and current decay with time under biasing. The aim of this paper is to provide an overview of the structural and optoelectronic properties of melanins and to bring to focus current gaps and challenges in the development of melanin-based materials for bioelectronics. Starting from commercial samples, the paper surveys different melanin-type materials with special emphasis on the potential of polydopamine (pDA), a highly adhesive mussel-inspired melanin-type platform, for incorporation in optoelectronic devices. Simple chemical tailoring procedures for engineering pDA-based n-type polymers and photoresponsive materials for photocapacitive sensors are eventually illustrated.

Although it has long been known that the peculiar electronic-ionic conductor behavior of eumelanin is critically dependent on hydration, the detailed mechanisms by which water-polymer interactions control and affect the conduction properties have remained largely obscure. In this paper, we report a remarkable anisotropy and giant polarization effect in a synthetic eumelanin (TEGMe) chemically functionalized with hydrophilic TEG residues. FT-IR analyses of water sorption isotherms and AC measurements were consistent with a microporous structure binding or hosting mainly isolated water molecules. In contrast, similar experiments on a commercial synthetic eumelanin (AMe) used as a reference were suggestive of a bulk macroporous scaffold binding or hosting liquid water. These data disclosed for the first time the differential impact on eumelanin conductivity of vapor, liquid and ice-like forms of water adsorbed onto or embedded into the polymer layer. It is thus demonstrated, for the first time, that hydration controls the conduction properties of eumelanin in a more complex manner than is commonly believed, involving, besides the reported semiquinone comproportionation equilibria, the mode of interaction of water molecules as governed by both the chemical and morphological features of the polymer.

Hysteresis behaviour of the current-voltage characteristics collected on spin coated synthetic eumelanin layer embedded in the Au/eumelanin/ITO/glass structure is shown. The effect has been observed under dark both in air and vacuum environment and its magnitudehas been found related to the eumelanin hydration state. Moreover, in vacuum and under white light illumination, enhancement of the hysteresis loop area respect to those collected under dark has been observed. Space charge storage and charge trapping/detrapping as possible mechanisms responsible of the observed current-voltage behaviour are discussed. Preliminary experimental results have evidenced the possible integration of eumelanin layers in electro-optical charge storage based memory devices.

Nowadays considerable efforts are devoted to the synthesis of low bandgap conjugated polymers forapplication in organic polymer solar cells. A large variety of low bandgap polymers are prepared byalternating copolymerization of electron-donating donor and electron-withdrawing acceptor units. Theinteraction between these two units can reduce the polymer bandgap, increasing the sunlight absorption.Benzothiadiazole is commonly used as acceptor block unit in low bandgap polymers. In this contributionwe investigate the supramolecular organization and optical properties of thin films of conjugated polymersconsisting of benzothiadiazole and thiophene with electron-withdrawing difluorovinylene, andelectron-donating vinylene substituents. Atomic force microscopy and spectroscopic ellipsometry areexploited for the analysis of the morphology and optical transitions, respectively. It is found that F-atomsin the vinylene unit yield a blue-shift of the absorption peaks of 0.2 eV respect to the hydrogenated polymerand an increase in the absorption coefficient of fluorinated polymers, which indicates their potentialapplication as photovoltaic material. The morphology evolution of the conjugated polymers blended witha fullerene derivate ([6,6]-phenyl C61-butyric acid methyl ester, PCBM) is also investigated by atomic forcemicroscopy.

Synthetic melanin based metal-insulator-semiconductor devices are fabricated for the first time thanks to silicon surface wettability modification by using dielectric barrier discharge plasma. Ambipolar charge trapping in air and ion drift mechanisms under vacuum are identified by capacitance-voltage hysteresis loops. These results aim to foresee the possible integration of synthetic melanin layers as a novel capacitor in organic polymer based devices.

The electrical transport across a biomimetic interface made up of spin coated melanin layers on nanotextured silicon surfaces with different texturing features and wetting properties is discussed. Nanotexturing allows, under certain conditions, the melanin to anchor better on a hydrophobic silicon surface, overcoming the hydrophilic melanin-hydrophobic silicon interface issue. The feature of the electrical signal transduction across such a structure was studied by impedance spectroscopy and found to be influenced by the nano-texturing chemistry and surface morphology. The effects of a voltage pulse, as external stimulus modifying the electrical transport mechanisms, and retention of the subsequently achieved carrier transport conditions have been elucidated. The results suggest a possible exploiting of this circuit element for bio and environmental molecules' sensing.

The memory-like behavior of melanin biopolymer under electrical stimuli is shown throughelectrical transport characterization performed on melanin based metal insulator semiconductorstructures on silicon. The presence of a memory window and retention behavior is verified bycapacitance-voltage read outs before and after the application of voltage pulses. Interestingly, thesephenomena occur without the presence of metallic nanoclusters enclosed in the melanin matrix.Charge trapping is considered the main mechanism responsible for the melanin memory-likecharacter. The inability to erase the memory window has been ascribed to the permanentpolarization effect during the application of the voltage pulse.

We report on the optical and photo-physical properties of a fluorinated poly(p-phenylenevinylene) derivative,namely poly(2-methoxy-5-[(2-ethylhexyl)oxy]-1,4-phenylenedifluorovinylene) (MEH-PPDFV)and we compare them with those of the well-known non fluorinated reference system, poly(2-methoxy-5-[(2-ethylhexyl)oxy]-1,4-phenylenevinylene) (MEH-PPV) synthesized with the same procedure.Remarkable blue-shifts of absorption and emission spectra of MEH-PPDFV with respect to MEH-PPVare observed, due to the larger distortion from planarity of the fluorinated species. In addition, theblue-shift for optical transitions in absorption spectra is more pronounced than in emission ones, sincethe molecule conformation in the excited states is more planar than in the ground one.Microsecond photo-induced absorption spectra of MEH-PPDFV reveal three bands possessing spectralproperties and/or kinetics different from those observed for MEH-PPV. The assignment of these transitionsis provided in terms of free and trapped polarons as well of triplet excitons. Free-polarons have anintrinsic decay constant of 3 ms, while the trapping dynamics has a longer kinetics of 40 ms. The tripletexciton, instead, shows a monoexponetial decay behavior of constant about 10 ms.

The integration of biopolymers into hybrid electronics is one of the up to date issues in view of the achievement of fully bio-compatible devices. Among 'hot topics' in bio-polymer research, synthetic melanin or, briefly, "melanin", has been recently recognized as a quite intriguing macromolecule thanks to its multifunctional optoelectronic properties. To date, melanin transport properties have been mainly enlightened on pellets, while optical absorption and conductivity properties have been investigated on melanin layers deposited on quartz and indium tin oxide/glass. The unavailability of suitable procedures to improve or promote adequate self assembling of melanin layer deposition onto substrate of interest in organic and solid state electronics (hybrid) like silicon substrates, prevent interesting studies on such structures. The reason stems basically on the difference between the hydrophilic nature of the melanin and the hydrophobic one of the supports (mostly of silicon). However, our group solved this issue and was able to tailor a melanin based metal/insulator/metal and metal/insulator/silicon structures, where synthetic melanin was embedded as the insulating part. This allowed to disclose interesting features related to data storage capabilities of melanin layers deposited on indium tin oxide/glass and silicon never investigated so far. In this work we show an overview on our recent mentioned results, and particular attention is paid on structures on silicon substrates. The use of pSi and nSi substrates and measurements under different environment conditions has enabled to gain insight into ambipolar electrical transport mechanisms, still unexplored. These results constitute a first important basic insight into melanin-based bio inspired structures and represent a significant step towards their integration in several kinds of hybrid organic polymer-based devices.

Colloidal white emitting nanostructures were successfully fabricated by covalently binding a blue emitting oligofluorene at the surface of silica beads, that incorporate orange luminescent colloidal CdSe@ZnS quantum dots (QDs). White light was achieved by carefully tuning the size of the QDs to complementarily match the emission color of the blue fluorophore and taking into account the delicate balance between the emission of the QDs in the core of the silica beads and the amount of the organic dye bound to the silica surface. The proposed approach is highly versatile as it can be extended to the fabrication of a variety of luminescent hybrid nano-objects, playing with the complementarity of the emission color of the inorganic and organic fluorophores at the nanoscale. This journal is © the Partner Organisations 2014.

Anthocyanins, extracted from grape skin (Vitis vinifera), were dissolved in ultrapure aqueous subphaseand an oligophenylenevinylene derivative was spread on the subphase surface. Such oligomer waschosen as anionic counterpart of hydrosoluble anthocyanins in order to perform a LangmuireSchäferfilm of the dyad. Interface interactions between oligophenylenevinylene derivative and anthocyaninswere studied by Brewster angle microscopy and reflection spectroscopy. Additionally, the oligomerexhibits a chemical structure able to ensure an enhancement of the stability under UVevisible irradiationsof the film of the dyad without any variation of the natural pigment absorption in the visible range.The visible spectra of cast anthocyanins film and LangmuireSchäfer oligomer/anthocyanins film afterexposure to 254 nm irradiation showed a remarkable increase of the film stability, probably due to thescreening effect of the oligomer. Preliminary test of a LangmuireSchäfer film of oligophenylenevinylenederivative/anthocyanins as a herbicide sensor showed that sensing is completely reversible, stable andrepeatable.

In this article a study of chemiresistor sensors based on Single and Multi Wall Carbon Nanotube films deposited at low temperature by means of a spray technique is presented. A dispersion of nanotube powder in a non-polar 1,2-Dichloroethane solvent was used as starting solution. Electron Microscopy in Scanning and Transmission mode were used in order to verify the morphological properties of the deposited films. The conductivity of carbon nanotubes (CNTs) was measured in two organic solvent vapors environments: 2-propanol and carbon-tetrachloride. The solvents used are characterized by different polarities. The results show that the electrical resistance of the sensors increases when exposed to solvent vapors. Finally the effect of Teflon-like and Melanin coatings on the sensitivity yield is presented and discussed.

Three new 2DepeA dyes (TK4, TK5 and TK6), composed of diarylamine donor groups, a dibenzofulvenethiophenecore as the p-bridge, and a cyanoacrylic acid anchoring group as the acceptor, have beensuccessfully designed, synthesized, and characterized both experimentally and computationally. Theperformance in DSSC solar cells has been also studied. Octyloxy chains were introduced on the backboneof the dye, in order to increase donor capability, avoid aggregation side effects and increase physicalinsulation between electrolyte system and the TiO2 layer. The dye containing the octyloxy chains on thedonor group and two thiophene ring as an extension of p-bridge showed the best photovoltaic performancewith a maximum of solar energy-to-electricity conversion yield of 7.8% under AM 1.5 irradiation(100 mW/cm2).

Fully fluorinated arylenevinylene polymers havebeen synthesized via a methodology based on the Stillecross-coupling reaction and characterized by FTIR spectroscopyand MALDI-TOF mass spectrometry. Investigation ofthin film properties by cyclic voltammetry and ellipsometryshows that complete substitution of hydrogen atoms withfluorine atoms on the conjugated backbone of the poly(arylenevinylene)s results in a strong increase of the band gap.

A general method to synthesize conjugated molecules with a benzofulvene core is reported. Up to four conjugated substituents have been introduced via a three-step sequence including (1) synthesis of 1,2-bis(arylethynyl)benzenes; (2) exo-dig electrophilic cyclization promoted by iodine; and (3) cross-coupling reaction of the resulting bis-iodobenzofulvenes with organoboron, organotin, or ethynyl derivatives under Pd catalysis. Structural aspects of the new compounds are discussed.

This review reports a survey of our recent results on the synthesis of arylenevinylene polymers and oligomers selectivelyfunctionalized with fluorine atoms on aromatic and/or vinylene units. The synthetic methods developed are based on Pd-catalyzedorganometallic cross-coupling reactions and in particular on the Stille coupling between vinyl organotin derivatives and aromatic halides.Several compounds have been synthesized, which differ for the number and position of the fluorine atoms on the conjugated backbone,even combined with other functional groups. The effects of fluorination on optical properties both in solution and solid state arediscussed.

Functionalization with fluorine atoms represents a versatile structural modification tofinely tune both the emission colour and the electronic properties of organic and organometallicelectroluminescent compounds. This paper reports an overview of our systematic investigation onthe design and synthesis of the fluorinated version of two important classes of materials for organiclight emitting diodes (OLEDs), namely poly(arylenevinylene)s and phosphorescent phenylpyridineIridium complexes. Synthetic pathways based on organometallic methodologies affordingselectively fluorinated molecular structures will be discussed together with a summary of the effectof fluorination on the optical properties of the resulting materials. In particular we will highlight thepossibilities offered by the organometallic methodologies as straightforward and resourceful toolsto provide a wide series of fluorinated molecular architectures with high regio- andstereoselectivity, mild experimental conditions and good yields.

There has been growing interest in developing new semiconducting polymers for applications in optoelectronics (OLEDs) due to their exceptional processability and appealing characteristic of manipulating electronic and optical properties by tuning of molecular structure and self-assembling. This study is an investigation on the interplay among supermolecular organization and optical properties of thin films of the poly[2-(2-ethylhexyloxy)-5-methoxy]-1, 4-phenylenedifluorovinylene(MEH-PPDFV) conjugated polymer, which has fluorinated vinylene units. This interplay is elucidated exploiting atomic force microscopy, spectroscopy ellipsometry, photoluminescence and electroluminescence. Thin films of MEH-PPDFV have been deposited by drop casting on indiumtin- oxide (ITO), quartz and glass substrates. The dependence of polymer chains self-organization and morphology on substrate surface is presented. Furthermore, it is demonstrated that the presenceof F-atoms in the vinylene units of the MEH-PPDFV yields a blue optical band gap with the maximum of the fundamental HOMO-LUMO transition at 331 nm and photoluminescence at 458 nm. The OLED built with the above polymer shows a very stable blue-greenish electroluminescence that is also achieved at 504 nm.

Selective imaging of lysosomes by fluorescence microscopy using specific fluorescent probes allows the study of biological processes and it is potentially useful also for diagnosis. Lysosomes are involved in numerous physiological processes, such as bone and tissue remodeling, plasma membrane repair, and cholesterol homeostasis, along with cell death and cell signaling. Despite the great number of dyes available today on the market, the search for new fluorescent dyes easily up-taken by cells, biocompatible and bearing bright and long-lasting fluorescence is still a priority. Methods: Two thiophene-based fluorescent dyes, TC1 and TC2, were synthetized as lysosome-specific probes. Results: The new dyes showed high selectivity for fluorescent staining and imaging of lysosomes and disclosed high photostability, low toxicity and pH insensitivity in the range 2-10. Conclusions: The TC dyes exhibited high co-localization coefficients (>95%) and moderate quantum yields. They showed high biocompatibility and long-term retention, important features for biological applications. General significance: The results of the present work disclose a new class of organic dyes with potential wide applications as specific and efficient lysosome probes in the study of various biological processes.