title: 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.
authors.affiliation: Department of Chemistry, Washington University , St. Louis, Missouri 63130-4889, United States.
authors.forename: Hyun Suk
authors.initials: HS
authors.lastname: Kang
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, Baltimore County , Baltimore, Maryland 21250-0001, United States.
authors.forename: Nopondo N
authors.initials: NN
authors.lastname: Esemoto
authors.affiliation: Department of Chemistry, University of California , Riverside, California 92521-0403, United States.
authors.forename: James R
authors.initials: JR
authors.lastname: Diers
authors.affiliation: Photosynthetic Antenna Research Center, Washington University , St. Louis, Missouri 63130-4889, United States.
authors.forename: Dariusz M
authors.initials: DM
authors.lastname: Niedzwiedzki
authors.affiliation: Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269-3060, United States.
authors.forename: Jordan A
authors.initials: JA
authors.lastname: Greco
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, Baltimore County , Baltimore, Maryland 21250-0001, United States.
authors.forename: Joshua
authors.initials: J
authors.lastname: Akhigbe
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, Baltimore County , Baltimore, Maryland 21250-0001, United States.
authors.forename: Zhanqian
authors.initials: Z
authors.lastname: Yu
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, Baltimore County , Baltimore, Maryland 21250-0001, United States.
authors.forename: Chirag
authors.initials: C
authors.lastname: Pancholi
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, Baltimore County , Baltimore, Maryland 21250-0001, United States.
authors.forename: Ganga Viswanathan
authors.initials: GV
authors.lastname: Bhagavathy
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, Baltimore County , Baltimore, Maryland 21250-0001, United States.
authors.forename: Jamie K
authors.initials: JK
authors.lastname: Nguyen
authors.affiliation: Department of Chemistry, Washington University , St. Louis, Missouri 63130-4889, United States.
authors.forename: Christine
authors.initials: C
authors.lastname: Kirmaier
authors.affiliation: Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269-3060, United States.
authors.forename: Robert R
authors.initials: RR
authors.lastname: Birge
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, Baltimore County , Baltimore, Maryland 21250-0001, United States.
authors.forename: Marcin
authors.initials: M
authors.lastname: Ptaszek
authors.affiliation: Department of Chemistry, Washington University , St. Louis, Missouri 63130-4889, United States.
authors.forename: Dewey
authors.initials: D
authors.lastname: Holten
authors.affiliation: Department of Chemistry, University of California , Riverside, California 92521-0403, United States.
authors.forename: David F
authors.initials: DF
authors.lastname: Bocian
mesh_terms: D011166:Porphyrins / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D011166:Porphyrins; C452433:bacteriochlorin; C006969:chlorin