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EXCITED STATES OF SIX‐MEMBERED N ‐HETEROCYCLES. FLUORESCENCE, PHOSPHORESCENCE AND ACID‐BASE EQUILIBRIA OF FIVE MONO‐ AND DIAZA‐PHENANTHRENES IN THE LOWEST EXCITED (τ,τ) STATES
Author(s) -
Grabowska A.,
Pakuła B.,
Panciř J.
Publication year - 1969
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.1751-1097.1969.tb05706.x
Subject(s) - phosphorescence , excited state , chemistry , fluorescence , ground state , phenanthrenes , excitation , molecule , photochemistry , absorption (acoustics) , reactivity (psychology) , atomic physics , physics , organic chemistry , medicine , phenanthrene , alternative medicine , quantum mechanics , pathology , acoustics
— Acid‐base equilibria of five azaphenanthrenes (1‐and 4‐aza; 1,10‐, 1,7‐, and 4,7‐diaza) in the two lowest excited (τ,τ) states have been determined by Förster's cycle. Pure electronic levels of the free bases and their conjugate acids have been located from the absorption, fluorescence and phosphorescence spectra. In diazaphenanthrenes the increase of the first pK a and the decrease of the second pK a under excitation has been observed, and an explanation is offered. In many cases the reactivity of the molecule excited to the lowest triplet state differs considerably from that in the ground state. The Pariser‐Pam‐Pople (PPP) calculations of the free bases have been performed. From the theoretical results, the changes of the net charge on nitrogen atoms under excitation and the magnitude of the S‐T splitting in the L a and L b states have been discussed and compared with experiment.