Quartarolo Angelo Domenico, Lanzo Ida, Sicilia Emilia, Russo Nino
Dipartimento di Chimica and Centro di Calcolo ad Alte Prestazioni per Elaborazioni Parallele e Distribuite-Centro di Eccellenza MURST, Università della Calabria, I-87030, Arcavacata di Rende, Italy.
Phys Chem Chem Phys. 2009 Jun 14;11(22):4586-92. doi: 10.1039/b819064j. Epub 2009 Mar 17.
A time-dependent density functional theory study (TD-DFT) is presented regarding the substituent effects on the Q-bands of two classes of non-planar phthalocyanines: the alpha-octaphenyl and p-alpha-octamethoxyphenyl substituted compounds, in their free-base and zinc complex forms. Singlet vertical excitation energies, computed at the PBE0/SVP//BP86/SVP level of theory also including bulk solvent effects (COSMO model), resulted within 0.1 eV of experiment. The experimental red-shift for the Q-band, going from the phenylated to the methoxyphenylated case, was well-reproduced theoretically and in the latter case it was found to depend mainly on the nature of the substituents and partly on structure distortion effects. The energetic gap between the singlet ground and first triplet excited state was calculated in solvent to be 1.28 eV for the free-base phthalocyanine (H2Pc) and 1.45 eV for the unsubstituted zinc complex (ZnPc) and lower than 0.98 eV for all the other compounds, which is the energetic lower limit for a molecule to act as photosensitiser in photodynamic therapy according to a Type II reaction mechanism. As a consequence, since this property-requirement for drugs used in photodynamic therapy is not fulfilled by the investigated near-infrared photosensitizers, they cannot be proposed as candidates for their use in this medical treatment.
本文提出了一项含时密度泛函理论研究（TD-DFT），涉及两类非平面酞菁化合物：α-八苯基和对-α-八甲氧基苯基取代化合物，以其游离碱和锌配合物形式存在时，取代基对其Q带的影响。在PBE0/SVP//BP86/SVP理论水平下计算的单重态垂直激发能，同时包括体相溶剂效应（COSMO模型），结果与实验值的误差在0.1 eV以内。从苯基化到甲氧基苯基化的情况下，Q带的实验红移在理论上得到了很好的再现，并且在后一种情况下发现其主要取决于取代基的性质，部分取决于结构畸变效应。在溶剂中计算得到，游离碱酞菁（H2Pc）的单重态基态与第一三重态激发态之间的能隙为1.28 eV，未取代的锌配合物（ZnPc）为1.45 eV，而所有其他化合物的能隙均低于0.98 eV，根据II型反应机制，这是分子在光动力疗法中作为光敏剂起作用的能量下限。因此，由于所研究的近红外光敏剂不满足光动力疗法中所用药物的这一性质要求，它们不能被提议作为这种医学治疗的候选药物。
