Edible Long-Afterglow Photoluminescent Materials for Bioimaging.

Confining luminophores into modified hydrophilic matrices or polymers is a straightforward and widely used approach for afterglow bioimaging. However, the afterglow quantum yield and lifetime of the related material remain unsatisfactory, severely limiting the using effect especially for deep-tissue time-resolved imaging. This fact largely stems from the dilemma between material biocompatibility and the quenching effect of water environment. Herein an in situ metathesis promoted doping strategy is presented, namely, mixing ≈10-3 weight ratio of organic-emitter multicarboxylates with inorganic salt reactants, followed by metathesis reactions to prepare a series of hydrophilic but water-insoluble organic-inorganic doping afterglow materials. This strategy leads to the formation of edible long-afterglow photoluminescent materials with superior biocompatibility and excellent bioimaging effect. The phosphorescence quantum yield of the materials can reach dozens of percent (the highest case: 66.24%), together with the photoluminescent lifetime lasting for coupes of seconds. Specifically, a long-afterglow barium meal formed by coronene salt emitter and BaSO4 matrix is applied into animal experiments by gavage, and bright stomach afterglow imaging is observed by instruments or mobile phone after ceasing the photoexcitation with deep tissue penetration. This strategy allows a flexible dosage of the materials during bioimaging, facilitating the development of real-time probing and theranostic technology.

Spectroscopic Identification of the Charge Transfer State in Thiophene/Fullerene Heterojunctions: Electroabsorption Spectroscopy from GW/BSE Calculations.

Creation of charge transfer (CT) states in bulk heterojunction systems such as C60/polymer blends is an important intermediate step in the creation of carriers in organic photovoltaic systems. CT states generally have small oscillator strengths in linear optical absorption spectroscopy owing to limited spatial overlap of electron and hole wave functions in the CT excited state. Electroabsorption spectroscopy (EA) exploits changes in wave function character of CT states in response to static electric fields to enhance detection of CT states via nonlinear optical absorption spectroscopies. A 4 × 4 model Hamiltonian is used to derive splittings of even and odd Frenkel (FR) excited states and changes in wave function character of CT excited states in an external electric field. These are used to explain why FR and CT states yield EA lineshapes which are first and second derivatives of the linear optical absorption spectrum. The model is applied to ammonia-borane molecules and pairs of molecules with large and small B-N separations and CT or FR excited states. EA spectra are obtained from differences in linear optical absorption spectra in the presence or absence of a static electric field and from perturbative sum over states (SOS) configuration interaction singles χ(2) and χ(3) nonlinear susceptibility calculations. Good agreement is found between finite field (FF) and SOS methods at field strengths similar to those used in EA experiments. EA spectra of three C60/oligothiophene complexes are calculated using the SOS method combined with GW/BSE methods. For these C60/oligothiophene complexes, we find several CT states in a narrow energy range in which charge transfer from the thiophene HOMO level to several closely spaced C60 acceptor levels yields an EA signal around 10% of the signal from oligothiophene.

Charge transfer excitons in π-stacked thiophene oligomers and P3[Alkyl]T crystals: CIS calculations and electroabsorption spectroscopy.

Poly(3-alkylthiophenes) (P3[Alkyl]T) exhibit high mobility and efficiency of formation of polaronic charge carriers generated by light absorption, thus finding applications in field effect devices. Excited states of π-stacked dimers of tetra-thiophene oligomers (T4), infinite isolated polythiophene (PT) chains, and P3[Alkyl]T crystals are modeled using configuration interaction singles (CIS) calculations. Excited states in cofacial T4 dimers are mostly localized Frenkel states except for two low energy charge transfer (CT) exciton states, which become the ionization potential and electron affinity levels of T4 molecules at large dimer separation. The lowest excited states in infinite, isolated PT chains and P3[Alkyl]T crystals are intra-chain excitons where the electron and hole are localized on the same chain. The next lowest excited states are interchain, CT excitons in which the electron and hole reside on neighboring chains. The former capture almost all optical oscillator strength and the latter may be a route to efficient formation of polaronic charge carriers in P3[Alkyl]T systems. Changes in optical absorption energies of T4 dimers as a function of molecular separation are explained using CIS calculations with four frontier orbitals in the active space. Shifts in optical absorption energy observed on going from isolated chains to P3[Alkyl]T lamellar structures are already present in single-particle transition energies induced by direct π-π interactions at short range. The electroabsorption spectrum of T4 dimers is calculated as a function of dimer separation and states that are responsible for parallel and perpendicular components of the spectrum are identified.

A computational study of anisotropic charge transport in air-stable fluorinated benzobisbenzothiophene (FBBBT) derivatives.

A computational study of anisotropical charge transport properties of fluorinated benzobisbenzothiohphene derivatives (FBBBT) is presented. The values of IPadia of all FBBBTs are found in the range of 6.00-6.20 eV inferring the fact that the investigated compounds have ambient air-stability. In addition, the energy levels of FBBBT s are found to be lower than those of benzobisbenzothiophene (BBBT) compound indicating higher charge carrier stability in the former. Hirshfield surface analyses showed that, in all the studied compounds, the principal identifiable interaction were mostly due to F⋯H and H⋯H intermolecular couplings with no contribution from S⋯S bondings. The calculated maximum µhole(µelec) value of the compounds FBBBT-a and FBBBT-b was found to be 0.483 (0.794) cm2V- 1s- 1 and 0.688 (0.542) cm2V- 1s- 1 respectively in the direction of transistor channel (Φ = 93.39 ∘(273.30∘) for FBBBT-a and Φ = 92.24 ∘/272.72 ∘ for FBBBT-b). For FBBBT-c, the maximum µelec(µhole) value of 0.933 (0.233) cm2V- 1s- 1 appeared for Φ = 0 ∘/179.90 ∘. In addition, the compounds FBBBT-a and FBBBT-b possess two additional fluorine atoms attached at the X positions in the backbone, which result in an increment in µelec values (1.4 times and 0.78 times higher than µhole) in these two compounds at a particular crystal direction.