Electronic Communication in Closely Connected BODIPY-Based Bichromophores

Abstract

A small series of closely spaced, bichromophoric boron dipyrromethene (BODIPY) derivatives has been examined by optical spectroscopy and compared to the corresponding mononuclear dyes. The compounds vary according to the site of attachment and also by the nature of alkyl or aryl substituents incorporated into the dipyrrin backbone. Excitonic coupling splits the lowest-energy absorption transition in each case, but to highly variable degrees. There are also marked changes in the fluorescence quantum yields across the series but much less variation in the excited-state lifetimes. After comparing different models, it is concluded that the ideal dipole approximation gives a crude qualitative representation of the observed splitting of the absorption transition, but the extended dipole approach is not applicable to these systems. Agreement is substantially improved by employing a model that takes into account the dihedral angle between the planes of the two dipyrrin units. The large variation in radiative rate constants, and those for the accompanying nonradiative processes, is accountable in terms of electronic coupling and/or intensity borrowing between the two excitonic states. In all cases, the dihedral angle between the two BODIPY units plays a key role.

Solid‐State Emission from Mono‐ and Bichromophoric Boron Dipyrromethene (BODIPY) Derivatives and Comparison with Fluid Solution

“…In fluid solution, the Φ F falls rapidly as the temperature rises. These qualitative findings confirm that some type of structural distortion is responsible for the restricted emission seen in fluid solution at ambient temperature …”

“…These qualitative findings confirmt hat some type of structural distortion is responsible for the restricted emission seen in fluid solution at ambient temperature. [36,37] Figure 1. Normalized absorption(black curve), fluorescence(grey curve) and excitation(opencircles)spectra recorded for 2 in CH 2 Cl 2 solution at room temperature.…”

Light-Harvesting Crystals Formed from BODIPY-Proline Biohybrid Conjugates: Antenna Effects and Excitonic Coupling

“…It is common practice to use the ratio ( R ) of oscillator strengths for the H- and J-bands to estimate the average angle (α) between the transition dipole moment vectors according to eq . , In our case, this expression leads to an average value for α of 53°. Because excitonic coupling occurs between pairs of chromophores distributed around the channel, it is not possible to compare this angle with an experimental measurement.…”

Effects of Naphthyl Connectivity on the Photophysics of Compact Organic Charge-Transfer Photoredox Catalysts

“…We therefore set out here to characterize the impact of naphthyl connectivity. It is noted that while this investigation solely relies on the phenoxazine architecture, efforts are made to conduct studies such that results can help inform other systems (e.g., phenazine, , phenothiazine, − flavin, acridinium, − xanthene, and BODIPY , ) with different applications. That said, phenoxazine derivatives are themselves increasingly important in the field of organic photoredox catalysis, and a significant secondary aim of the current work is to refine our understanding of this architecture and how excited-state processes can be controlled.…”