A spectroscopic and computational study of the singlet and triplet excited states of synthetic β-functionalized chlorins

• Published in: Chemical physics 2003-11, Vol.294 (3), p.285-303
• Main Authors: Brückner, Christian, McCarthy, Jason R, Daniell, Heather W, Pendon, Zeus D, Ilagan, Robielyn P, Francis, Tasha M, Ren, Lei, Birge, Robert R, Frank, Harry A
• Format: Article
• Language: English
• Subjects: Absorption; EPR; Fluorescence; Molecular orbital calculation; Porphyrins; Transient absorption
• ISSN: 0301-0104
• DOI: 10.1016/S0301-0104(03)00282-9

This paper presents a comparative investigation of the absorption, fluorescence, electron paramagnetic resonance (EPR), and transient triplet–triplet absorption spectroscopic properties and triplet state dynamics of two functionalized, synthetic, meso-phenylchlorins. The chromophores investigated are the novel 2-hydroxy-3-oxa-5,10,15,20-tetrakisphenylchlorin ( 3) and the known 2,3-dioxo-5,10,15,20-tetrakisphenylchlorin ( 4). In these chromophores, one peripheral CHCH bond of the parent porphyrin meso-tetrakisphenylporphyrin (TPP, 1) was formally replaced by a CH(OH)O (lactol) or a β-diketone moiety. The spectroscopic data are compared with results from investigations on the parent porphyrin TPP studied here and the parent chlorin 5,10,15,20-tetrakisphenylchlorin (TPC, 2) from the literature. The spectroscopic observables are examined both qualitatively within the framework of the four orbital model and quantitatively using MNDO-PSDCI methods. The results delineate the role of β-lactol and β-dicarbonyl moieties in controlling the electronic and spectroscopic properties of these chromophores. This investigation serves as the foundation from which to derive a general understanding of the effects of β-functionalization on the electronic properties of chlorin-type chromophores. This knowledge is required for the design and understanding of long-wavelength absorbing and fluorescing chromophores to be used in light harvesting systems and photomedicine.