Five-Coordinate Indium(III) Porphyrins with Hydroxy and Carboxy BODIPY as Axial Ligands: Synthesis, Characterization and Photophysical Studies

Luminescent Bis(amidinate) Indium Complexes

Bis-amidinate indium(III) monochlorides [(tBuN)2C(Ph)]2InCl (1), [(tBuN)2C(2-naphthyl)]2InCl (2), [(tBuN)2C(2-anthryl)]2InCl (3), [(tBuN)2C(9-anthryl)]2InCl (4), [(tBuN)2C(9-phenanthryl)]2InCl (5), and [(tBuN)2C(1-pyrene)]2InCl (6) were prepared by the reaction of the corresponding Li-amidinate ligand with InCl3. Single crystal X-ray analysis of compounds 1, 2, 4, and 5 reveals that the In(III) center is bound with two chelating amidinate ligands. The overall coordination geometry around In(III) is distorted trigonal bipyramidal with the chloride occupying one of the equatorial positions. The photophysical properties of these compounds have been analyzed. Compounds 2-6 are emissive in the solution state. The 9-anthryl substituted compound 4 was found to exhibit a maximum quantum yield of 45.5% in dichloromethane. Compound 3 has a maximum lifetime of 11 ns in solution. Theoretical studies were performed to validate the photophysical properties observed in these compounds.

Azophenine as Central Core for Efficient Light Harvesting Devices

The notoriously non-luminescent uncycled azophenine (Q) was harnessed with Bodipy and zinc(II)porphyrin antennas to probe its fluorescence properties, its ability to act as a singlet excited state energy acceptor and to mediate the transfer. Two near-IR emissions are depicted from time-resolved fluorescence spectroscopy, which are most likely due to the presence of tautomers of very similar calculated total energies (350 cm^-1 ; DFT; B3LYP). The rates for energy transfer, k_ET (S₁ ), for ¹ Bodipy*→Q are in the order of 10¹⁰ -10¹¹  s^-1 and are surprisingly fast when considering the low absorptivity properties of the lowest energy charge transfer excited state of azophenine. The rational is provided by the calculated frontier molecular orbitals (MOs) which show atomic contributions in the C₆ H₄ C≡CC₆ H₄ arms, thus favoring the double electron exchange mechanism. In the mixed-antenna Bodipy-porphyrin star molecule, the rate for ¹ Bodipy*→porphyrin has also been evaluated (≈16×10¹⁰  s^-1 ) and is among the fastest rates reported for Bodipy-zinc(II)porphyrin pairs. This astonishing result is again explained from the atomic contributions of the C₆ H₄ C≡CC₆ H₄ and C≡CC₆ H₄ arms thus favouring the Dexter process. Here, for the first time, this process is found to be sensitively temperature-dependent. The azophenine turns out to be excellent for electronic communication.

Amphiphilic BODIPY-Hydroporphyrin Energy Transfer Arrays with Broadly Tunable Absorption and Deep Red/Near-Infrared Emission in Aqueous Micelles

BODIPY-hydroporphyrin energy transfer arrays allow for development of a family of fluorophores featuring a common excitation band at 500 nm, tunable excitation band in the deep red/near-infrared window, and tunable emission. Their biomedical applications are contingent upon retaining their optical properties in an aqueous environment. Amphiphilic arrays containing PEG-substituted BODIPY and chlorins or bacteriochlorins were prepared and their optical and fluorescence properties were determined in organic solvents and aqueous surfactants. The first series of arrays contains BODIPYs with PEG substituents attached to the boron, whereas in the second series, PEG substituents are attached to the aryl at the meso positions of BODIPY. For both series of arrays, excitation of BODIPY at 500 nm results in efficient energy transfer to and bright emission of hydroporphyrin in the deep-red (640-660 nm) or near-infrared (740-760 nm) spectral windows. In aqueous solution of nonionic surfactants (Triton X-100 and Tween 20) arrays from the second series exhibit significant quenching of fluorescence, whereas properties of arrays from the first series are comparable to those observed in polar organic solvents. Reported arrays possess large effective Stokes shift (115-260 nm), multiple excitation wavelengths, and narrow, tunable deep-red/near-IR fluorescence in aqueous surfactants, and are promising candidates for a variety of biomedical-related applications.

Rational Design of Emissive NIR-Absorbing Chromophores: Rh(III) Porphyrin-Aza-BODIPY Conjugates with Orthogonal Metal-Carbon Bonds

The facile synthesis of Group 9 Rh(III) porphyrin-aza-BODIPY conjugates that are linked through an orthogonal Rh-C(aryl) bond is reported. The conjugates combine the advantages of the near-IR (NIR) absorption and intense fluorescence of aza-BODIPY dyes with the long-lived triplet states of transition metal rhodium porphyrins. Only one emission peak centered at about 720 nm is observed, irrespective of the excitation wavelength, demonstrating that the conjugates act as unique molecules rather than as dyads. The generation of a locally excited (LE) state with intramolecular charge-transfer (ICT) character has been demonstrated by solvatochromic effects in the photophysical properties, singlet oxygen quantum yields in polar solvents, and by the results of density functional theory (DFT) calculations. In nonpolar solvents, the Rh(III) conjugates exhibit strong aza-BODIPY-centered fluorescence at around 720 nm (ΦF =17-34 %), and negligible singlet oxygen generation. In polar solvents, enhancements of the singlet-oxygen quantum yield (ΦΔ =19-27 %, λex =690 nm) have been observed. Nanosecond pulsed time-resolved absorption spectroscopy confirms that relatively long-lived triplet excited states are formed. The synthetic methodology outlined herein provides a useful strategy for the assembly of functional materials that are highly desirable for a wide range of applications in material science and biomedical fields.

Highly efficient near IR photosensitizers based-on Ir–C bonded porphyrin-aza-BODIPY conjugates

Novel orthogonally arranged Ir(iii) porphyrin-aza-BODIPY conjugates exhibit strong absorbance in the near infrared region and have unusually high singlet oxygen quantum yields, since they act as unique molecules rather than as dyads.

Benefits of using BODIPY–porphyrin dyads for developing deep-red lighting sources

The syntheses, as well as the photophysical and electrochemical characterization, of two novel BODIPY–porphyrin dyads and their first application in lighting schemes are provided.

Cunning metal core: efficiency/stability dilemma in metallated porphyrin based light-emitting electrochemical cells

The syntheses, the photophysical/electrochemical characterization, and the first application in LECs of different metallated porphyrins are provided.