Dynamics of Intramolecular Energy Hopping in Multi-Bodipy Self-Assembled Metallocyclic Species: A Tool for Probing Subtle Structural Distortions in Solution

Abstract

The intramolecular excitation energy transfer (EET) processes in a series of fluorescent-unquenched, self-assembled metallocycles consisting of spatially fixed-separated and parallel-aligned Bodipy chromophores, are investigated here by steady-state and femtosecond-fluorescence upconversion measurements in the solution phase. These multi-Bodipy macrocycles, namely, the rhomboid (A1), the tetragon (A2) and the hexagon (A3), are formed via temperature-regulated Pt­(II)–pyridyl coordination and consist, respectively, of two, four, and six Bodipy subunits, which are locked at the corners and aligned with their long molecular axes perpendicular to the rigid polygonal frame formed by the alternating B···Pt­(II) connectivities. Extensive simulations and fits to the experimental fluorescence anisotropy decays r(t) show that EET within the cyclic scaffolds is quite uniform and much faster than the intrinsic decay rate of the Bodipy’s. The equalization of the excitation survival probabilities over time of all chromophores is found to be dependent upon the size of the macrocycle. From the observed dynamics supported by geometry optimization calculations, it is concluded that, in contrast to the model compound A1, in the large macrocycles the perfect parallel orientation of the Bodipy dipoles is lifted through limited out-of-plane distortions of the metallocyclic framework from a planar conformation. Additionally, we show that, as opposed to analogous covalent macrocycles, the survival probability of excitons as well as the degree of symmetry distortion and homogeneity in dipole spacing remains nearly intact as the size of the macrocycle increases from tetragon to hexagon.

Self-Assembly of Bodipy-Derived Extended π-Systems

“…103106 The coordination-driven self-assembly of Bodipy dyes (49, 5255) and platinum complexes (50 and 51) has been studied in rhomboid type cavitand (Figure 19). 107,108 The Bodipy derivative (49) was prepared by replacing the tetrahedral fluorine atoms present in the Bodipy core with ethynyl pyridine linker. The Bodipy moiety was vertically aligned to the plane of the ethynyl pyridine units.…”

Toward Prediction of Nonradiative Decay Pathways in Organic Compounds II: Two Internal Conversion Channels in BODIPYs

“…molecular dynamics (ab initio, − QM/MM, − classical, etc. ), density functional theory (DFT)-based methods (TDDFT, ,,,− ,,,− etc. ), configuration interaction (CI)-based methods (CIS/CID/CISD, ,,− SOS-CIS­(D), SACCI, ,, etc.…”

Excitation/detection energy controlled anisotropy dynamics in asymmetrically cyano substituted tri-podal molecules

“…The anisotropy, when detected in the few tens of ps timescale, is a valuable tool for determining (i) the angle between the absorption and emission dipole moments (via the value of the initial anisotropy r 0 ), as well as (ii) the possible energy transfer/delocalization phenomena. 17,19,[25][26][27]31,34,35,53,[58][59][60][61][62][63][64][65][66] The latter phenomena are highly dependent on the initial excited state, that is populated, or the amount of excess energy that is provided to the system, especially in compounds with multiple chromophores.…”