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  1. Free, publicly-accessible full text available July 25, 2024
  2. Abstract

    A series of chlorin‐bacteriochlorin dyads (derived from naturally occurring chlorophyll‐a and bacteriochlorophyll‐a), covalently connected either through themeso‐aryl or β‐pyrrole position (position‐3) via an ester linkage have been synthesized and characterized as a new class of far‐red emitting fluorescence resonance energy transfer (FRET) imaging, and heavy atom‐lacking singlet oxygen‐producing agents. From systematic absorption, fluorescence, electrochemical, and computational studies, the role of chlorin as an energy donor and bacteriochlorin as an energy acceptor in these wide‐band‐capturing dyads was established. Efficiency of FRET evaluated from spectral overlap was found to be 95 and 98 % for themeso‐linked and β‐pyrrole‐linked dyads, respectively. Furthermore, evidence for the occurrence of FRET from singlet‐excited chlorin to bacteriochlorin was secured from studies involving femtosecond transient absorption studies in toluene. The measured FRET rate constants,kFRET, were in the order of 1011 s−1, suggesting the occurrence of ultrafast energy transfer in these dyads. Nanosecond transient absorption studies confirmed relaxation of the energy transfer product,1BChl*, to its triplet state,3Bchl*. The3Bchl* thus generated was capable of producing singlet oxygen with quantum yields comparable to their monomeric entities. The occurrence of efficient FRET emitting in the far‐red region and the ability to produce singlet oxygen make the present series of dyads useful for photonic, imaging and therapy applications.

     
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  3. Abstract

    A series ofmeso‐biphenyl linked chlorin and bacteriochlorin dimers, derived from naturally occurring chlorophyll (Chl‐a) and bacteriochlorophyll (BChl‐a) were synthesized in 32 % to 44 % yields and characterized, as photosynthetic antenna mimics, and a new class of singlet oxygen producing agents. The dimers are characterized by absorption, fluorescence, electrochemical, spectroelectrochemical and computational methods to evaluate their physico‐chemical properties, and to identify ground and excited state interactions. Evidence of excited energy exchange among the chromophores in the dimer is derived from femtosecond transient absorption spectral studies. Rate constants for excitation hopping were in the order of 1011 s−1, indicating occurrence of efficient processes. Nanosecond transient absorption studies confirmed relaxation of the singlet excited chlorin and bacteriochlorin dimers to their corresponding triplet states (3Chl* and3Bchl*). As predicted by the established energy level diagrams, both3Chl* and3Bchl* are shown to be capable of producing singlet oxygen with appreciable quantum yields (ϕSO∼0.3).

     
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  4. Combined SFG/MD analysis together with spectral calculations revealed that type III antifreeze proteins adsorbed at the air–water interface maintains a native state and adopts an orientation that leads to a partial decoupling of its ice-binding site from water.

     
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