NANObits: Effect of Chlorin Structure on Theoretical Electronic Absorption Spectra and on the Energy Released by Porphyrin-Based Photosensitizers

Abstract

Supporting Info

Marcela Palma^†, Gloria I. C

rdenas-Jir

n*^† and M. Isabel Men

ndez Rodr

guez*^‡

Laboratorio de Qu

mica Te

rica, Departamento de Ciencias del Ambiente, Facultad de Qu

mica y Biolog

a, Universidad de Santiago de Chile, USACH Casilla 40, Correo 33, Santiago, Chile, and Departamento de Qu

mica F

sica y Anal

tica, Facultad de Qu

mica. Universidad de Oviedo, C/Juli

n Claver

a 8, 33006 Oviedo, Asturias, Spain

J. Phys. Chem. A, 2008, 112 (51), pp 13574–13583

DOI: 10.1021/jp804350n

Publication Date (Web): November 24, 2008

†

Universidad de Santiago de Chile.

* Authors to whom correspondence should be addressed: e-mail gloria.cardenas@usach.cl (G.I.C.-J.) or isabel@uniovi.es (M.I.M.R.).

‡

Universidad de Oviedo.

Abstract

In this work eight porphyrins (p) and eight chlorins (c) are theoretically characterized [BLYP/6-31G(d)] in their singlet and triplet states. Nine of them (1_p, 1_c, 2_p, 3_p, 4_p, 5_p, 6_c, 7_c, and 8_c) have already been synthesized and are in trial use in photodynamic therapy (PDT). The seven remaining were built up as chlorins analogous to porphyrins 2_p−5_p and porphyrins analogous to chlorins 6_c−8_c. The aim is to investigate the effect of the chlorin structure on the Q-band of electronic spectra at BLYP/6-31G(d) (gas phase, methanol solution) and at BHANDHLYP/6-31+G(d) (methanol solution), and on the triplet → singlet energy emission, as these two factors determine the quality of a good photosensitizer. It is found that meso substituents lead to greater geometry distortions than β-substituents in both porphyrins and chlorins and in both singlet and triplet states. In methanol solution, chlorin-like structures with β substitution present significantly red-shifted Q-bands in comparison with their porphyrin analogues, so they would be better photosensitizers than porphyrins. Concerning to the triplet → singlet energy emission calculated in methanol solution, three porphyrins (4_p, 6_p, and 8_p) and all the studied substituted chlorins could be useful to generate active ¹O₂. 4_c would be the best photosensitizer, as it absorbs the largest wavelength in the therapeutic window (approximately 690 nm) and releases the amount of energy closest to the required one (1.22 eV).