Theoretical studies on photodissociation of carbazole in high excited triplet states

Advances in Molecular Relaxation and Interaction Processes Pub Date : 1982-09-01 DOI:10.1016/0378-4487(82)80075-7

Josep Planelles, Francisco Tomas, Rogelio Montañana

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Abstract

A qualitative and semiquantitative explanation of “double flash” photochemical behaviour of carbazole is found by means of Molecular Orbital studies of ground and excited states of carbazole and carbazyl radical using the CNDO/S method. The need to excite to quite high energy triplet states in order to produce the homolytic breakdown of N-H bond is justified by the fact that the triplet states of carbazole correlating with ground and first excited states of carbazyl radical are, respectively, T₁₅ and T₁₂. These triplet states appear to be populated indirectly by means of the second flash that at first populates some other nearby triplet states (T₉ to T₁₁) from T₁ followed by an Internal Conversion (IC) from these to the T₁₅ and T₁₂ states. This procedure is favoured by the energy lowering of the T₁₅ and T₁₂ triplet states on enlarging the N-H bond and by the important contamination of these two states owed to spin-orbit coupling.

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高激发态下咔唑光解的理论研究

利用CNDO/S方法对咔唑和咔酰自由基的基态和激发态进行了分子轨道研究，对咔唑的“双闪”光化学行为进行了定性和半定量的解释。咔唑的三重态与咔唑基自由基的基态和第一激发态分别为T15和T12，这一事实证明，为了产生N-H键的均裂破坏，需要激发到相当高的能量三重态。这些三重态似乎是通过第二次闪光间接填充的，第二次闪光首先从T1填充附近的一些其他三重态(T9到T11)，然后从这些状态到T15和T12状态进行内部转换(IC)。由于N-H键的扩大，T15和T12三重态的能量降低，以及自旋轨道耦合对这两个态的重要污染，有利于这一过程。

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Advances in Molecular Relaxation and Interaction Processes

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