title: Directly Connected AzaBODIPY-BODIPY Dyad: Synthesis, Crystal Structure, and Ground- and Excited-State Interactions.
abstract: Directly connected, strongly interacting sensitizer donor-acceptor dyads mimic light-induced photochemical events of photosynthesis. Here, we devised a dyad composed of BF2-chelated dipyrromethene (BODIPY) directly linked to BF2-chelated tetraarylazadipyrromethene (azaBODIPY) through the β-pyrrole position of azaBODIPY. Structural integrity of the dyad was arrived from two-dimensional NMR spectral studies, while single-crystal X-ray structure of the dyad provided the relative orientation of the two macrocycles to be ∼62°. Because of direct linking of the two entities, ultrafast energy transfer from the (1)BODIPY* to azaBODIPY was witnessed. A good agreement between the theoretically estimated Förster energy transfer rate and experimentally determined rate was observed, and this rate was found to be higher than that reported for BODIPY-azaBODIPY analogues connected with spacer units. In agreement with the free-energy calculations, the product of energy transfer, (1)azaBODIPY* revealed additional photochemical events such as electron transfer leading to the creation of BODIPY(•+)-azaBODIPY(•-) radical ion pair, more so in polar benzonitrile than in nonpolar toluene, as evidenced by femtosecond transient spectroscopic studies. Additionally, the spectral, electrochemical, and photochemical studies of the precursor compound azaBODIPY-dipyrromethane also revealed occurrence of excited-state events. In this case, electron transfer from the (1)azaBODIPY* to dipyrromethane (DPM) yielded DPM(•+)-azaBODIPY(•-) charge-separated state. The study described here stresses the role of close association of the donor and acceptor entities to promote ultrafast photochemical events, applicable of building fast-response optoelectronic and energy-harvesting devices.
authors.affiliation: †Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
authors.forename: Sunit
authors.initials: S
authors.lastname: Kumar
authors.affiliation: ‡Department of Chemistry, University of North Texas, 1155 Union Circle, No. 305070, Denton, Texas 76203-5017, United States.
authors.forename: Habtom B
authors.initials: HB
authors.lastname: Gobeze
authors.affiliation: †Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
authors.forename: Tamal
authors.initials: T
authors.lastname: Chatterjee
authors.affiliation: ‡Department of Chemistry, University of North Texas, 1155 Union Circle, No. 305070, Denton, Texas 76203-5017, United States.
authors.forename: Francis
authors.initials: F
authors.lastname: D'Souza
authors.affiliation: †Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
authors.forename: Mangalampalli
authors.initials: M
authors.lastname: Ravikanth
mesh_terms: D001372:Aza Compounds / Q000737:chemistry*; D001896:Boron Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D060326:Chemistry Techniques, Synthetic; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008968:Molecular Conformation
chemical_list: C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001372:Aza Compounds; D001896:Boron Compounds