Luminescence of BODIPY and Dipyrrin: An MCSCF Comparison of Excited States

Abstract

Low lying electronic states of the highly fluorescent BODIPY (boron dipyrromethene, 1) and its nonemissive cousin dipyrrin (2) were investigated by state-of-the-art quantum chemical methods. The opposed luminescence of 1 and 2 is explained by discovering distinct structural and energetic features for the intersection of the ground and first excited singlet state potential energy surfaces, S(0) and S(1). In accessing the intersection region, a B-N σ-bond in 1 has to be broken-an energetically prohibitive change on the nonemissive decay channel. On the contrary, 2 is deactivated via an energetically accessible S(0)/S(1) intersection point. Details of S(0), S(1), S(2), and T(1) wave functions for various regions of the potential energy surfaces were described. Unnoted features for multidimensional vectors that represent S(0) → S(1) and S(0) → T(1) transitions are reported. These correlations regarding S(0) → S(1) and S(0) → T(1) multidimensional vectors were also shown to apply to two highly fluorescent molecules: indole and coumarin.

Fluorescence Quenching in BODIPY Dyes: The Role of Intramolecular Interactions and Charge Transfer

“…Therefore, the nonradiative decay is not expected to play a major role. Dede et al . reported another S 1 /S 0 conical intersection, associated with the BN bond breaking in the nearly planar geometry (located at the MCSCF level).…”

“…A variety of theoretical methods were previously employed to study excited states of BODIPY and its derivatives, including DFT based (TDDFT, ∆SCF, ROKS, DFT‐MRCI), single reference wavefunction‐based (ADC(2), CC2, SAC‐CI), mixed (SOS‐CIS(D)/TDDFT), multireference (CASSCF, CASPT2, XMCQDPT2), semiempirical and machine learning methods. The S 1 state of various BODIPY compounds is well described by a single excitation from the highest occupied (HOMO) to the lowest unoccupied molecular orbital (LUMO), having a high oscillator strength which manifests in the intense and sharp absorption peaks .…”

Supramolecular Photothermal Effects: A Promising Mechanism for Efficient Thermal Conversion

“…To improve the photothermal conversion efficiency, the fluorescent emission path should be inhibited as completely as possible. A representative example concerning the energy‐level‐dependent energy conversion was shown by a pair of boron‐dipyrromethene (BODIPY) compounds . For the BODIPY molecule, the energy of the S 1 state is much lower than the CI, so the de‐excitation pathway prefers fluorescent emission rather than thermal relaxation.…”

“…Diamagnetic metal ions, such as Mg 2+ and Zn 2+ , may enhance fluorescence by fixing the molecular configuration of the dye via coordination through the following mechanism: coordination increases the energy level of the conical intersection of the ligand and the radiative deexcitation process becomes energetically more favorable . Moreover, diamagnetic metal ions also inhibit intramolecular motions.…”

Theoretical studies on the electronic structure and spectroscopic properties of transition metals bis(dipyrrinate)s

“…Currently, the detailed quantum-chemical analysis allows to solve many fundamental and applied problems. They deal with understanding molecular structure and its influence on the spectral-luminescent properties as well as possible controlled changes for the organic dyes properties and their derivatives including BODIPY [20][21][22] and porphyrins complexes with transition metals [23][24][25][26]. However, due to the large size, complex structure and the presence of d-metals in the composition of complexing agents, the works on quantum-chemical calculations of [M 2 L 2 ] are very few [27,28].…”