激发态卟啉衍生物研究(Ⅶ)——取代基对卟啉—硝基苯化合物发光特性的影响

STUDY ON EXCITED PORPHYRINS (Ⅷ) SUBSTITUENT EFFECT ON LUMINESCENCE OF COVALENTLY LINKED PORPHYRIN-NITROBENZENE COMPOUNDS

本文报导共价链相连的X-P-Y“三合板”型化合物在二甲基甲酰胺(DMF)和苯溶液中的发光特性。结果发现:引入取代基X=Cl—,CH_3O—和Y=苯、硝基苯对中心卟啉的吸收和荧光光谱均无明显影响,仅其峰值频率将因溶剂不同而有所偏移。此外,由Cl—取代的卟啉—苯的荧光强度总比CH_3O—取代时高;若将Y取代基由苯改换为硝基苯时,将使CH_3O—P—Y化合物的荧光增强,但在Cl—P—Y化合物中则出现相反的趋势。不论在何种化合物中,在Y取代基中的苯环上引入NO_2—基后,均可使其消光系数减小,而且当硝基在邻位取代时,这一效应更为显著。所有这些变化规律均不因溶剂不同而异。如果我们认为X—P—Y化合物的发光强度变化和其中心的卟啉大环上的π电子云密度偏移有规律性的关联,那么上述的一些取代基效应是可以理解的。进而,我们认为:本文所报导的事实将有助于充实巧妙设计高效利用太阳能的分子体系的科学依据。

The luminescence of covalently linked 'triad' compounds X-P-Y have been studied in DMF and benzene solutions. It is found that the attachment of sub-stituent X = CI, CH3O-as well as Y= phenyl(B) and nitrophenyl group(NB) has no detectable effect on both absorption and luminescencs spectra of the central porphyrin P, although a little solvent-dependent shift in their maximum frequency is observed. The substitutions, however, lead to a change in the luminescence intensity, particularly that of vibronic band. In these cases, the luminescence of Cl-attached P-B compounds is always more intense as compared with the rompounds with CH3O substituent as the X moiety. The replacement of phenyl substituent by nitrophenyl in Y moiety of compounds CH3O-P-Y leads to an enhancement of their luminescence,but the opposite trend is observed in the Cl-substitued compounds Cl-P-Y upon the same structural change in Y substituent. In both cases,the substitution of -NO2 at ortho position of phenyl ring of substituent Y shows again so-called 'Ortho effeect' at we reported previously in compounds of nitroporphyrins. These pictures are the same in both polar and apolar solvents and seem to be understandable by a tentative assumption that the luminescence intensity of these compounds is regularly coorelated to the substitution-induced shift of eletron density in the electronic system of porphyrin macrocycle. Thus,it is believed that these findings reported here will offer some hint leading to improve our scientific knowledge for an ingenious design of artificial molecular system for utilization of solar energy with high efficiency.