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A THEORETICAL TREATMENT OF THE ELECTRONIC STATES OF THIONINE AND RELATED MOLECULES
Author(s) -
SOMMER U.,
KRAMER H. E. A.
Publication year - 1971
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1971.tb06130.x
Subject(s) - thionine , excited state , singlet state , chemistry , protonation , molecule , singlet fission , triplet state , character (mathematics) , ground state , atom (system on chip) , reactivity (psychology) , photochemistry , computational chemistry , atomic physics , physics , ion , organic chemistry , geometry , mathematics , electrode , computer science , embedded system , electrochemistry , medicine , alternative medicine , pathology
— –Problems associated with the protolytic equilibria of thionine and related molecules in their lowest excited electronic states were investigated. The theoretical arguments are based on semi‐empirical SCF MO (CI) calculations for the π‐electronic system of these molecules; all singly excited configurations were included in the CI. The results indicate that the basic form of thionine in its ground, first excited singlet and lowest triplet state is protonated at the heterocyclic N atom. The difference of the p K values of these three states can be explained in terms of the calculated charge densities. The photochemical reactivity of the lowest triplet of the acidic form of thionine ( 3 TH 2 2+ ) differs greatly from that of the lowest triplet of the basic form ( 3 TH + ). Some arguments for the assignment of nπ* character to 3 TH 2 2+ and ππ* character to 3 TH + are advanced.