Related Experiment Video
Updated: Jun 15, 2025
Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
Exciton Coupling and Charge Transfer Dynamics in Zn(II) Complexes of π-Extended Dipyrrins
Dabin Kim1, Luca Ravotto1,2, April Bialas3
1Department of Chemistry, School of Arts and Sciences, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
None:
Dipyrrins form a group of versatile chromophores, which find use as laser dyes as well as in light harvesting and bioimaging applications. The mode of the central ion coordination and the ensuing molecular geometry play a key role in the photophysics of dipyrrins, whereby some complexes are brightly fluorescent and some completely lack emissivity. However, the relationship between the structure and excitation dynamics in dipyrrins is still poorly understood. Here, we used a range of spectroscopic methods to investigate the photophysics of Zn(II) complexes of meso-Ar-2,2'-di-tert-butoxycarbonyl-dibenzodipyrrins (BDP; Ar = 4-MeO2C-C6H4). In particular, two-dimensional electronic spectroscopy (2DES) was used to characterize the initial excited states in a homoleptic bis-dipyrrinate Zn(BDP)2, in which two dipyrrin ligands are oriented in a nonorthogonal geometry. From the position of the peaks in the 2DES spectra and spectral modeling, the initial excited states of Zn(BDP)2 were assigned to excitonic states. The low oscillator strength, associated with excitation to the lower excitonic state, is responsible in part for the weak emissivity of Zn(BDP)2, contrasting the bright fluorescence of mono-dippyrinate Zn(BDP)X. Femtosecond (fs-), nanosecond (ns-) transient absorption (TA), and time-resolved fluorescence spectroscopies were used to monitor the solvent-dependent evolution of the excitonic states, which appear to evolve into an intermediate state possibly with charge transfer character. Taken together, our findings reveal a significant impact of both structural and environmental factors on the photophysics of dipyrrins and present the first example of the application of 2DES to investigate excitonic states in a system where the interacting chromophores are held together via coordination of an optically neutral metal ion. On a broader scale, we demonstrate that nonorthogonal bis-dipyrrin complexes constitute a versatile model for studying exciton coupling and associated energy and charge dynamics.
Related Concept Videos
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:42Valence Bond Theory
01:11Aryldiazonium Salts to Azo Dyes: Diazo Coupling
01:14π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...