Effects of Strong Electronic Coupling in Chlorin and Bacteriochlorin Dyads

Abstract

Achieving tunable, intense near-infrared absorption in molecular architectures with properties suitable for solar light harvesting and biomedical studies is of fundamental interest. Herein, we report the photophysical, redox, and molecular-orbital characteristics of nine hydroporphyrin dyads and associated benchmark monomers that have been designed and synthesized to attain enhanced light harvesting. Each dyad contains two identical hydroporphyrins (chlorin or bacteriochlorin) connected by a linker (ethynyl or butadiynyl) at the macrocycle β-pyrrole (3- or 13-) or meso (15-) positions. The strong electronic communication between constituent chromophores is indicated by the doubling of prominent absorption features, split redox waves, and paired linear combinations of frontier molecular orbitals. Relative to the benchmarks, the chlorin dyads in toluene show substantial bathochromic shifts of the long-wavelength absorption band (17-31 nm), modestly reduced singlet excited-state lifetimes (τS = 3.6-6.2 ns vs 8.8-12.3 ns), and increased fluorescence quantum yields (Φf = 0.37-0.57 vs 0.34-0.39). The bacteriochlorin dyads in toluene show significant bathochromic shifts (25-57 nm) and modestly reduced τS (1.6-3.4 ns vs 3.5-5.3 ns) and Φf (0.09-0.19 vs 0.17-0.21) values. The τS and Φf values for the bacteriochlorin dyads are reduced substantially (up to ∼20-fold) in benzonitrile. The quenching is due primarily to the increased S1 → S0 internal conversion that is likely induced by increased contribution of charge-resonance configurations to the S1 excited state in the polar medium. The fundamental insights gained into the physicochemical properties of the strongly coupled hydroporphyrin dyads may aid their utilization in solar-energy conversion and photomedicine.

Amphiphilic BODIPY-Hydroporphyrin Energy Transfer Arrays with Broadly Tunable Absorption and Deep Red/Near-Infrared Emission in Aqueous Micelles

“…Negligible PET for BC5-BDP can be explained by the likely higher oxidation potential of the phenylacetylene-substituted bacteriochlorin compared to the phenyl-substituted one. 30,59 …”

Synthesis and photophysical characteristics of 2,3,12,13-tetraalkylbacteriochlorins

“…[4][5][6][7][8][9] Over some years now, a de novo synthesis route has been developed to gain access to diverse substituted bacteriochlorins. By modification of the substituents attached to the pyrrolic units and/or the meso-positions, the bacteriochlorins can be tailored with regards to the position of the long-wavelength absorption band (ranging from 690 nm to 900 nm), [14][15][16][17] the polarity (hydrophobic, amphiphilic, or hydrophilic 18 ) and the presence of derivatizable groups for bioconjugation or buildingblock applications. The gem-dimethyl group secures the pyrroline ring from adventitious oxidation that would lead to unsaturated products (i.e., chlorins and porphyrins).…”

“…[10][11][12][13] The synthetic method relies on the self-condensation of a dihydrodipyrrin-acetal (1-acetal), which contains a dimethyl group integral to the reduced, pyrroline ring and an acetal unit located at the pyrroline a-position (Scheme 1). 8,9,15,17,[19][20][21] A key aspect of the self-condensation of a dihydrodipyrrinacetal is that different acidic conditions (acid composition and concentration) and dihydrodipyrrin-acetal concentrations can lead to distinct outcomes with regards to the macrocycles formed: a free base 5-unsubstituted bacteriochlorin (HBC-type macrocycle), a free base 5-methoxybacteriochlorin (MeOBCtype macrocycle), a free base B,D-tetradehydrocorrin (TDC-type macrocycle). By modification of the substituents attached to the pyrrolic units and/or the meso-positions, the bacteriochlorins can be tailored with regards to the position of the long-wavelength absorption band (ranging from 690 nm to 900 nm), [14][15][16][17] the polarity (hydrophobic, amphiphilic, or hydrophilic 18 ) and the presence of derivatizable groups for bioconjugation or buildingblock applications.…”

Switching sides—Reengineered primary charge separation in the bacterial photosynthetic reaction center

“…2 A and B) of all of the electronic states of the RC (Fig. 2 C-E) because they all involve P. The electronic structure of P can be viewed in analogy to the properties of strongly coupled tetrapyrrole dimers (63)(64)(65)(66)(67)(68). The highest occupied molecular orbital (HOMO) of P is an antibonding MO at higher energy than the HOMOs of the constituent BChls (P A and P B ) due to interactions between the 2 BChls.…”