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Tailoring Panchromatic Absorption and Excited-State Dynamics of Tetrapyrrole–Chromophore (Bodipy, Rylene) Arrays—Interplay of Orbital Mixing and Configuration Interaction

2017; American Chemical Society; Volume: 139; Issue: 48 Linguagem: Inglês

10.1021/jacs.7b09548

1943-2984

Amit Kumar Mandal, James R. Diers, Dariusz M. Niedzwiedzki, Gongfang Hu, Rui Liu, Eric J. Alexy, Jonathan S. Lindsey, David F. Bocian, Dewey Holten,

Perovskite Materials and Applications

Three sets of tetrapyrrole–chromophore arrays have been examined that exhibit panchromatic absorption across large portions of the near-ultraviolet (NUV) to near-infrared (NIR) spectrum along with favorable excited-state properties for use in solar-energy conversion. The arrays vary the tetrapyrrole (porphyrin, chlorin, bacteriochlorin), chromophore (boron-dipyrrin, perylene, terrylene), and attachment sites (meso-position, β-pyrrole position). In all, seven dyads, one triad, and nine benchmarks in toluene and benzonitrile were studied using steady-state and time-resolved absorption and fluorescence spectroscopy. The results were analyzed with the aid of density functional theory (DFT) and time-dependent DFT calculations. Natural transition orbitals (NTOs) were constructed to assess the net change in electron density associated with each NUV–NIR absorption transition. The porphyrin–perylene dyad P-PMI displays the most even spectral coverage from 400 to 700 nm, with an average ε ∼ 43 000 M–1 cm–1. A significant contributor is a chromophore-induced reduction in the configuration interaction involving the four frontier molecular orbitals of benchmark porphyrins and associated constructive/destructive transition-dipole interference that results in intense (ε ∼ 400 000 M–1 cm–1) NUV and weak (<20 000 M–1 cm–1) visible features. P-PMI has an S1 lifetime (τS) of 4.7 ns in toluene and 1.3 ns in benzonitrile. Bacteriochlorin analogue BC-PMI has more extended spectral coverage (350–750 nm) and τS = 2.8 ns in toluene and 30 ps in benzonitrile. Terrylene analogue P-TMI has intermediate optical characteristics with τS = 310 ps in toluene and 150 ps in benzonitrile. The NTOs for most arrays show that S0 → S1 primarily involves the tetrapyrrole, but for P-TMI the NTOs have electron density delocalized over the two units as a result of extensive orbital mixing. Collectively, the insights obtained should aid the design of tetrapyrrole-based architectures for panchromatic light-harvesting systems for solar-energy conversion.