Anthracene–BODIPY Cassettes: Syntheses and Energy Transfer

New 8-substituted BODIPY-based chromophores: synthesis, optical and electrochemical properties

BODIPY-based chromophores, in which an electron withdrawing difluoro-boraindacene fragment is connected via position 8 to different donor fragments, were synthesized. Their electrochemical and photophysical properties were studied. All compounds exhibit a quasi-reversible oxidation corresponding to the formation of a BODIPY π-radical cation at around 0.8 V vs. FeCp

Remarkable acceleration of template-directed photodimerisation of 9-phenylethynylanthracene derivatives assisted by complementary salt bridge formation

The photodimerisation of 9-phenylethynylanthracene-bound carboxylic acid monomers was remarkably accelerated in the presence of the complementary amidine dimer template.

A perylene bisimide derivative with pyrene and cholesterol as modifying structures: synthesis and fluorescence behavior

Intramolecular singlet–singlet excitation energy transfer from pyrene to perylene bisimide via Dexter mechanism and aggregate emission of perylene bisimide.

Quantum-Chemical Studies on Excitation Energy Transfer Processes in BODIPY-Based Donor-Acceptor Systems

BODIPY-based excitation energy transfer (EET) cassettes are experimentally extensively studied and serve as excellent model systems for the investigation of photophysical processes, since they occur in any photosynthetic system and in organic photovoltaics. In the present work, the EET rates in five BODIPY-based EET cassettes in which anthracene serves as the donor have been determined, employing the monomer transition density approach (MTD) and the ideal dipole approximation (IDA). To this end, a new computer program has been devised that calculates the direct and exchange contributions to the excitonic coupling (EC) matrix element from transition density matrices generated by a combined density functional and multireference configuration interaction (DFT/MRCI) calculation for the monomers. EET rates have been calculated according to Fermi's Golden Rule from the EC and the spectral overlap, which was obtained from the calculated vibrationally resolved emission and absorption spectra of donor and acceptor, respectively. We find that the direct contribution to the EC matrix element is dominant in the studied EET cassettes. Furthermore, we show that the contribution of the molecular linker to the EET rate cannot be neglected. In our best fragment model, the molecular linker is attached to the donor moiety. For cassettes in which the transition dipole moments of donor and acceptor are oriented in parallel manner, our results confirm the experimental findings reported by Kim et al. [J. Phys. Chem. A 2006, 110, 20-27]. In cassettes with a perpendicular orientation of the donor and acceptor transition dipole moments, dynamic effects turn out to be important.

Bodipy-C60 triple hydrogen bonding assemblies as heavy atom-free triplet photosensitizers: preparation and study of the singlet/triplet energy transfer

Supramolecular triplet photosensitizers based on hydrogen bonding-mediated molecular assemblies were prepared. Three thymine-containing visible light-harvesting Bodipy derivatives (B-1, B-2 and B-3, which show absorption at 505 nm, 630 nm and 593 nm, respectively) were used as H-bonding modules, and 1,6-diaminopyridine-appended C60 was used as the complementary hydrogen bonding module (C-1), in which the C60 part acts as a spin converter for triplet formation. Visible light-harvesting antennae with methylated thymine were prepared as references (B-1-Me, B-2-Me and B-3-Me), which are unable to form strong H-bonds with C-1. Triple H-bonds are formed between each Bodipy antenna (B-1, B-2 and B-3) and the C60 module (C-1). The photophysical properties of the H-bonding assemblies and the reference non-hydrogen bond-forming mixtures were studied using steady state UV/vis absorption spectroscopy, fluorescence emission spectroscopy, electrochemical characterization, and nanosecond transient absorption spectroscopy. Singlet energy transfer from the Bodipy antenna to the C60 module was confirmed by fluorescence quenching studies. The intersystem crossing of the latter produced the triplet excited state. The nanosecond transient absorption spectroscopy showed that the triplet state is either localized on the C60 module (for assembly B-1·C-1), or on the styryl-Bodipy antenna (for assemblies B-2·C-1 and B-3·C-1). Intra-assembly forward-backward (ping-pong) singlet/triplet energy transfer was proposed. In contrast to the H-bonding assemblies, slow triplet energy transfer was observed for the non-hydrogen bonding mixtures. As a proof of concept, these supramolecular assemblies were used as triplet photosensitizers for triplet-triplet annihilation upconversion.

Charge transfer in the electron donor-acceptor complexes of a meso-phenol BODIPY dye with chloranils and fullerenes

UV-Vis spectral investigations of electron donor-acceptor complexes of laser dye 2,6-Diethyl-4,4-difluoro-1,3,5,7-tetramethyl-8-(4'-hydroxyphenyl)-4-bora-3a,4a-diaza-s-indecene (1c) with chloranils and fullerenes are reported in toluene medium. Well defined charge transfer (CT) absorption bands have been located in the visible region. Oscillator strengths, transition dipole and resonance energies of the CT complexes have been estimated. Vertical ionization potential of 1c has been determined utilizing Mulliken's equation. A possible mechanism for the interaction between electronic subsystems of chloranils, [60]- and [70]fullerenes with three different BODIPY dyes (1a, 1b and 1c shown in Fig. 1) have been discussed in comparing the parameters like degree of charge transfer and binding constant in nonpolar toluene. Comparison of 1c complexes is done with DFT/B3LYP/6-31G optimized gas phase geometries.

Spectroscopic and crystallographic investigations of novel BODIPY-derived metal-organic frameworks

To explore new 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-derived metal-organic frameworks (MOFs), we employed 2,6-dicarboxyl-1,3,5,7-tetramethyl-8-phenyl-4,4-difluoroboradiazaindacene (H2L) as a ligand to successfully synthesize five coordination polymers, namely, {[Zn2(L)2(bpp)]·2H2O·2EtOH}n (1), {[Cd2(L)2(bpp)]·2H2O·EtOH}n (2), {[Cd2(L)(bpe)3(NO3)2]·2H2O·DMF·EtOH}n (3), {[Cd(L)(bpe)0.5(DMF)(H2O)]}n (4), and {[Cd(L)(bpe)0.5]·1.5H2O·DMF}n (5) (bpp = 1,3-bi(4-pyridyl)propane, bpe = 1,2-bi(4-pyridyl)ethane). Except for two 2D-layer coordination polymers 3 and 4, the rest samples exhibit 3D metal-organic frameworks with certain pore sizes, especially MOFs 1 and 5. Spectroscopic and crystallographic investigations demonstrate that the absorption and emission energies of the BODIPY chromophores are sensitive to the coordination modes. Moreover, in case 2, the transition metal centers coordinated with the dicarboxylate ligands L(2-) are capable of forming the two BODIPY units in coplanar arrangements (θ = 37.9°), simultaneously suppressing the uncommon J-dimer absorption band centered at 705 nm with a long tail into the near-infrared region at room temperature. On the other hand, in comparison with the ligand H2L, the emission of monomer-like BODIPY in case 3 is enhanced in the solid state by a considerably long distance between the parallel BODIPY planes (about 14.0 Å).

Halogenated boron-dipyrromethenes: synthesis, properties and applications

Synthesis and properties of halogenated boron-dipyrromethenes and their applications in developing various BODIPY systems are described in this review.

Synthesis and properties of novel star-shaped oligofluorene conjugated systems with BODIPY cores

Star-shaped conjugated systems with varying oligofluorene arm length and substitution patterns of the central BODIPY core have been synthesised, leading to two families of compounds, T-B1–T-B4 and Y-B1–Y-B4, with T- and Y-shaped motifs, respectively. Thermal stability, cyclic voltammetry, absorption and photoluminescence spectroscopy of each member of these two families were studied in order to determine their suitability as emissive materials in photonic applications.

Synthesis, characterization and photophysical properties of an acenaphthalene fused-ring-expanded NIR absorbing aza-BODIPY dye

The synthesis and characterization of an NIR absorbing acenaphthalene fused-ring-expanded aza-BODIPY dye.

Switching of the triplet excited state of styryl 2,6-diiodo-bodipy and its application in acid-activatable singlet oxygen photosensitizing

IodoBodipy-styrylBodipy dyads triplet photosensitizers were prepared (B-1 and B-2) which contain acid-responsive moiety. Both compounds show broadband visible light absorption, due to the resonance energy transfer (RET) between the two different visible light-harvesting Bodipy units. The photophysical properties of the dyads were studied with steady-state and nanosecond time-resolved transient absorption spectroscopy. The production of triplet excited state is switched ON or OFF by protonation/deprotonation of the amino group in the dyads. In the neutral form, the excited state is short-lived (<10 ns) and no singlet oxygen ((1)O2) photosensitizing was observed. Upon protonation, a long-lived triplet excited state was observed (τT = 3.1 μs) and the (1)O2 quantum yield (ΦΔ) is up to 73.8%. The energy levels of the components of the dyads were changed upon protonation and this energy level tuning exerts significant influence on the triplet state property of the dyad. Acid-activated shuffling of the localization of the triplet excited state between two components of a dyad was observed. Furthermore, we observed a rare example that a chromophore giving shorter absorption wavelength is acting as the singlet energy acceptor in RET. The experimental results were rationalized by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations.

Synthesis and properties of rhenium(I) bridged boron-dipyrromethene dyad

We synthesized the hexa-coordinated Re ( I ) bridged BODIPY dyad 1 in decent yield by thermal reaction of benzimidazole substituted BODIPY 2 with Re ( CO )5 Cl . The dyad 1 was characterized by 1 H , 13 C , 11 B , 19 F NMR, ESI-MS, FTIR, UV-vis, and electrochemical techniques. In Re ( I ) bridged dyad 1, the Re ( I ) ion is hexa-coordinated and coordinates with nitrogen atoms of two benzimidazole units, three axial carbonyl ligands and one chloride atom. The presence of three carbonyl groups in dyad 1 was verified by 13 C NMR and IR spectroscopy. The absorption and steady-state fluorescence spectra of Re ( I ) bridged BODIPY dyad showed a slightly broad and hypsochromically shifted absorption and emission bands compared to BODIPY 2. The electrochemical studies indicated that, the Re ( I ) bridge BODIPY dyad 1 was easy to reduce compared to BODIPY 2 supporting the electron deficient nature dyad upon Re ( I ) ion binding. The molecular structure of dyad 1 was further elucidated by DFT computational studies.

Red-light-absorbing diimine Pt(II) bisacetylide complexes showing near-IR phosphorescence and long-lived 3IL excited state of Bodipy for application in triplet-triplet annihilation upconversion

Bodipy is used for the preparation of Pt(II) bisacetylide complexes which show strong absorption of visible light and long-lived triplet state. Room temperature (RT) near-IR phosphorescence of Bodipy was observed. The π-conjugation framework of visible light-harvesting Bodipy ligand was connected to the Pt(II) center by the C≡C bond. The complexes were used as triplet photosensitizers for triplet-triplet annihilation (TTA) upconversion.

Asymmetric dinuclear bis(dipyrrinato)zinc(ii) complexes: broad absorption and unidirectional quantitative exciton transmission

Asymmetric, heteroleptic dinuclear bis(dipyrrinato)zinc(ii) complexes convey excitons quantitatively and rapidly across their structure from one end to the other.

Spiranic BODIPYs: a ground-breaking design to improve the energy transfer in molecular cassettes

From a flexible cassette it is possible to boost the EET by a simple spiranic design.

Structural modification strategies for the rational design of red/NIR region BODIPYs

The structure–property relationships of red/NIR region BODIPY dyes is analyzed, so that trends in their photophysical properties can be readily compared.

Axially bonded pentads constructed on the Sn(iv) porphyrin scaffold

Three pentads based on the Sn(iv) porphyrin scaffold were synthesized using three covalently linked dyads such as porphyrin–ferrocene, porphyrin–BODIPY and porphyrin–sapphyrin as axial units. The spectral, electrochemical and photophysical properties were studied for these dyads and pentads.

Triplet photosensitizers: from molecular design to applications

Triplet photosensitizers (PSs) are compounds that can be efficiently excited to the triplet excited state which subsequently act as catalysts in photochemical reactions. The name is originally derived from compounds that were used to transfer the triplet energy to other compounds that have only a small intrinsic triplet state yield. Triplet PSs are not only used for triplet energy transfer, but also for photocatalytic organic reactions, photodynamic therapy (PDT), photoinduced hydrogen production from water and triplet-triplet annihilation (TTA) upconversion. A good PS should exhibit strong absorption of the excitation light, a high yield of intersystem crossing (ISC) for efficient production of the triplet state, and a long triplet lifetime to allow for the reaction with a reactant molecule. Most transition metal complexes show efficient ISC, but small molar absorption coefficients in the visible spectral region and short-lived triplet excited states, which make them unsuitable as triplet PSs. One obstacle to the development of new triplet PSs is the difficulty in predicting the ISC of chromophores, especially of organic compounds without any heavy atoms. This review article summarizes some molecular design rationales for triplet PSs, based on the molecular structural factors that facilitate ISC. The design of transition metal complexes with large molar absorption coefficients in the visible spectral region and long-lived triplet excited states is presented. A new method of using a spin converter to construct heavy atom-free organic triplet PSs is discussed, with which ISC becomes predictable, C60 being an example. To enhance the performance of triplet PSs, energy funneling based triplet PSs are proposed, which show broadband absorption in the visible region. Applications of triplet PSs in photocatalytic organic reactions, hydrogen production, triplet-triplet annihilation upconversion and luminescent oxygen sensing are briefly introduced.

Photophysical and laser properties of cassettes based on a BODIPY and rhodamine pair

This work deals with the synthesis and the photophysical and laser properties of new BODIPY-rhodamine cassettes. These dyads differ in their rigid and conjugated spacer group (phenyl or acetylenephenyl) and in their linking positions (meta or para). The photophysical properties of these cassettes are controlled by the formation/opening of the spirolactone ring, which, in turn, switches off/on an energy-transfer process between the chromophores. Herein, we thoroughly describe the influence of the attached spacer group, as well as the distance and orientation between the donor-acceptor pair, on the excitation energy transfer. The observed fast dynamics and efficiency suggest that the process mainly takes place "through-bond", although the "through-space" mechanism also contributes to the whole process. As a result, efficient laser emission from the rhodamine is achieved upon excitation of the BODIPY, in particular for the cassette that contains an acetylenephenyl spacer group in a para disposition.

BODIPY-tetrazine derivatives as superbright bioorthogonal turn-on probes

The fastest and the brightest: A new design that intimately connects tetrazine to a BODIPY fluorophore enables exceptionally efficient energy transfer and quenching. Upon reaction of the tetrazine, the brightness of the fluorophore increases more than a thousand-fold, a fluorogenic activation up to two orders of magnitude greater than previously described.

Synthesis of conjugated BODIPYs via the Wittig reaction

A Wittig reaction was employed to synthesize conjugated BODIPYs in high yields by treating formylated BODIPYs with alkyl/aryl ylides under simple room temperature conditions. Treatment of 3,5-diformyl BODIPYs or α-formyl 3-pyrrolyl BODIPY with different alkyl/aryl ylides in CH2Cl2 at room temperature for 2 h followed by straightforward column chromatographic purification on silica afforded conjugated BODIPYs in ~65-90% yields. This is an alternate method to Knoevenagel and Heck reactions which have been used to synthesize such conjugated BODIPYs. The method works very efficiently, and we prepared 12 substituted BODIPYs including cholesterol-substituted BODIPYs to demonstrate the versatility of the reaction. The spectral, electrochemical, and fluorescence properties of these conjugated BODIPYs are also described.

Energy transfer cassettes based on organic fluorophores: construction and applications in ratiometric sensing

This tutorial review presents some recent developments in the construction and applications of cassettes based on resonance energy transfer between fluorescent dyes in the visible and infrared region. We focused on the contributions of different connections between the energy donor and acceptor according to the "through-space" and "through-bond" methods, and emphasised their applications in ratiometric sensing for the detection of ions and small molecules.