Photophysical properties of furan-bridged dimeric boron-dipyrromethene derivatives (BODIPYs)

In order to investigate the changes in the spectroscopic properties of dimeric boron-dipyrromethenes (BODIPYs), four BODIPY derivatives are synthesized, including a monomer BODIPY in which a furyl group is substituted at the meso position and a dimer BODIPY with a furan group as a bridge. The four synthesized BODIPY derivatives are characterized through nuclear magnetic resonance and mass spectrometry. Photophysical properties such as ultraviolet–visible absorbance and the fluorescence emission of monomers (mT1 and mT2) and dimers (biT1 and biT2) are studied in eight different solvents. In addition, the relationship of their structural properties and optical properties are also considered through density functional theory calculations. The covalent link between the two BODIPY units using a furan group has a profound effect on the optical properties of the dimeric BODIPYs. We believe that an understanding of the synthesis and physical properties of dimeric BODIPYs will have a promising perspective in designing new BODIPY derivatives and predicting their spectroscopic characteristics in the future.

BODIPY based red emitters: Synthesis, computational and biological studies

Donor-Acceptor type BODIPYs with strong absorption and fluorescence in the red region (550-800 nm) are reported. The aromatic groups like N-butylcarbazole/ N-butylphenothiazine/ benzothiadiazole were attached to the C-8 position of the BODIPY core with furan or thiophene spacers. TD-DFT studies indicated significant charge distribution between C-8 aromatic heterocycles and BODIPY core in all the molecules. The in-vitro studies of the N-butylcarbazole substituted BODIPYs indicated significant localization in the endoplasmic reticulum and lysosomes of the cancer cells. The BODIPYs showed decent cytotoxicity after 48 h incubation period (14.9 to 31.8 μM) in HeLa and A549 cancer cells, indicating their potential application as theranostic agents.

Influence of molecular design on radical spin multiplicity: characterisation of BODIPY dyad and triad radical anions

A strategy to create organic molecules with high degrees of radical spin multiplicity is reported in which molecular design is correlated with the behaviour of radical anions in a series of BODIPY dyads. Upon reduction of each BODIPY moiety radical anions are formed which are shown to have different spin multiplicities by electron paramagnetic resonance (EPR) spectroscopy and distinct profiles in their cyclic voltammograms and UV-visible spectra. The relationship between structure and multiplicity is demonstrated showing that the balance between singlet, biradical or triplet states in the dyads depends on relative orientation and connectivity of the BODIPY groups. The strategy is applied to the synthesis of a BODIPY triad which adopts an unusual quartet state upon reduction to its radical trianion.

Photophysical properties of some novel tetraphenylimidazole derived BODIPY based fluorescent molecular rotors

In this work, we present tetraphenylimidazole-based BODIPYs (HPIB1–HPIB4) as fluorescent molecular rotors exhibiting aggregation induced emission, solid state fluorescence and appreciable sensitivity towards viscosity.

Synthesis and biological studies of amphiphilic carbazole pyridinium conjugates

Amphiphilic carbazole pyridinium conjugates are synthesized and characterized by IR, 1H and [Formula: see text]C NMR and ESI-MS spectrometry. The pyridinium group is attached on the 3-position of the carbazole ring and long alkyl chains are linked to the central [Formula: see text] atom. The introduction of a pyridinium group afforded water-soluble carbazole derivatives with significant bathochromic shifts in their absorption and emission spectra. As compared to the parent [Formula: see text]-butylcarbazole compound, carbazole pyridinium conjugates exhibited 50 nm red-shifted absorption maxima. Similarly, the carbazole pyridinium conjugates displayed 143–147 nm red-shifted emission maxima in solution. In addition, large Stokes shifts (5747–7558 cm[Formula: see text] were observed for the conjugates in solution. The cell penetrable amphiphilic carbazole pyridinium conjugates exhibited cytoplasmic distribution in A549 cells.

Heavy-atom-free BODIPY photosensitizers with intersystem crossing mediated by intramolecular photoinduced electron transfer

Organic photosensitizers possessing efficient intersystem crossing (ISC) and forming long-living triplet excited states, play a crucial role in a number of applications. A common approach in the design of such dyes relies on the introduction of heavy atoms (e.g. transition metals or halogens) into the structure, which promote ISC via spin-orbit coupling interaction. In recent years, alternative methods to enhance ISC have been actively studied. Among those, the generation of triplet excited states through photoinduced electron transfer (PET) in heavy-atom-free molecules has attracted particular attention because it allows for the development of photosensitizers with programmed triplet state and fluorescence quantum yields. Due to their synthetic accessibility and tunability of optical properties, boron dipyrromethenes (BODIPYs) are so far the most perspective class of photosensitizers operating via this mechanism. This article reviews recently reported heavy-atom-free BODIPY donor-acceptor dyads and dimers which produce long-living triplet excited states and generate singlet oxygen. Structural factors which affect PET and concomitant triplet state formation in these molecules are discussed and the reported data on triplet state yields and singlet oxygen generation quantum yields in various solvents are summarized. Finally, examples of recent applications of these systems are highlighted.

Carbazole Substituted BODIPYs

Difluoroboron-dipyrromethenes (BODIPYs) are highly popular fluorescent dyes with applications as NIR probes for bioimaging, fluorescent tags/sensors and as photosensitizers in cancer therapy and organic photovoltaics. This review concentrates on the synthesis and spectral properties of BODIPY dyes conjugated with carbazole heterocycle. The carbazole is an electron rich tricyclic compound and due to its excellent electronic properties, it is extensively used in the production of electroluminescent materials and polymers. This review highlights the recent progress made on the series of BODIPY derivatives containing carbazole ring at alpha, beta, and meso-positions of the BODIPY skeleton. Carbazole based hybrid BODIPYs, carbazole linked aza-BODIPYs and carbazole-fused BODIPYs are also discussed.

Tuning the Photonic Behavior of Symmetrical bis-BODIPY Architectures: The Key Role of the Spacer Moiety

Herein we describe the synthesis, computationally assisted spectroscopy, and lasing properties of a new library of symmetric bridged bis-BODIPYs that differ in the nature of the spacer. Access to a series of BODIPY dimers is straightforward through synthetic modifications of the pending ortho-hydroxymethyl group of readily available C-8 (meso) ortho-hydroxymethyl phenyl BODIPYs. In this way, we have carried out the first systematic study of the photonic behavior of symmetric bridged bis-BODIPYs, which is effectively modulated by the length and/or stereoelectronic properties of the spacer unit. The designed bis-BODIPYs display bright fluorescence and laser emission in non-polar media. The fluorescence response is governed by the induction of a non-emissive intramolecular charge transfer (ICT) process, which is significantly enhanced in polar media. The effectiveness of the fluorescence quenching and also the prevailing charge transfer mechanism (from the spacer itself or between the BODIPY units) rely directly on the electron-releasing ability of the spacer. Moreover, the linker moiety can also promote intramolecular excitonic interactions, leading to excimer-like emission characterized by new spectral bands and the lengthening of lifetimes. The substantial influence of the bridging moiety on the emission behavior of these BODIPY dyads and their solvent-sensitivity highlight the intricate molecular dynamics upon excitation in multichromophoric systems. In this regard, the present work represents a breakthrough in the complex relationship between the molecular structure of the chromophores and their photophysical signatures, thus providing key guidelines for rationalizing the design of tailored bis-BODIPYs with potential advanced applications.

Phosphorescent rhenium-dipyrrinates: efficient photosensitizers for singlet oxygen generation

A series of rhenium(i) dipyrrinato complexes (Re1–Re8) have been prepared and characterized; their crystal structures, phosphorescence and singlet oxygen generation studies are reported.

Near infra-red dyes based on pyrene aza-BODIPYs

Donor–acceptor type pyrene substituted aza-BODIPYs are reported, and efficient energy transfer from pyrene moieties to the aza-BODIPY core caused significant red shifts in their absorption and emission spectra.

Solvent-Sensitive Emitting Urea-Bridged bis-BODIPYs: Ready Access by a One-Pot Tandem Staudinger/Aza-Wittig Ureation

Herein we describe the synthesis, and computationally aided photophysical characterization of a new set of urea-bridged bis-BODIPY derivatives. These new dyads are efficiently obtained by a one-pot tandem Staudinger/aza-Wittig ureation protocol, from easily accessible meso-phenyl ortho-azidomethyl BODIPYs. These symmetric bis-BODIPYs outstand by a high absorption probability and excellent fluorescence and laser emission in less polar media. Nevertheless, this emission ability decreases in more polar media, which is ascribed to a light-induced charge-transfer from the urea spacer to the dipyrrin core, a process that can be modulated by appropriate changes in the substitution pattern of the BODIPY core. Furthermore, this ureation protocol can also be employed for the direct conjugation of our BODIPY-azides to amine-containing compounds, thus providing access to fluorescent non-symmetric ureas.

Investigating the optical properties of BOIMPY dyes using ab initio tools

Using a computational approach combining Time-Dependent Density Functional Theory (TD-DFT) and second-order Coupled Cluster (CC2) approaches, we investigate the spectral properties of a large panel of BOIMPY dyes.

Donor–acceptor type A2B2porphyrins: synthesis, energy transfer, computational and electrochemical studies

Synthesis, photophysical, electrochemical and DFT studies of donor–acceptor type A₂B₂porphyrins and their Zn(ii) and Pd(ii) complexes have been described.

A new rod-shaped BODIPY-acetylene molecule for solution-processed semiconducting microribbons in n-channel organic field-effect transistors

A novel solution-processable BODIPY-based small molecule (BDY-PhAc-BDY) yields highly-crystalline, one-dimensional (1-D) microribbon semiconductors for organic field-effect transistors (OFETs).

Donor acceptor type ferrocene substituted aza-BODIPYs: Synthesis, optical and electrochemical studies

Two ferrocene substituted aza-BODIPYs and their corresponding aza-dipyrrins were synthesized and studied. All the compounds were characterized by HRMS, NMR, IR, absorption spectroscopy and cyclic voltammetry techniques. Absorption spectra indicated intramolecular electron transfer from the ferrocene to the aza-BODIPY core. The X-ray crystal structure of 1,7-bisferrocenyl-aza-BODIPY suggested moderate interactions between the ferrocene moieties and aza-BODIPYs core. Ferrocenyl-aza-BODIPYs were non-emissive due to electron transfer from ferrocene moieties to boron aza-dipyrrin core. However the emission of these compounds was dramatically enhanced by oxidizing the ferrocene moieties to ferrocenium ions, which prevents electron transfer between these moieties. Cyclic voltammetry studies suggested that aza-BODIPYs were easier to be reduced as compared to their corresponding aza-dipyrrins.

Push–pull flexibly-bridged bis(haloBODIPYs): solvent and spacer switchable red emission

Uncommon flexibly-bridged bis(BODIPYs) displaying switchable red emission are described.