Temperature dependence of the deactivation of electronically excited indazoles in solution

(15. X I . 75)Mechanistic studies on the photoisomerization of 2-alkyl-indazoles into 1 -alkylbenzimidazoles. 11. Primary photochemical processes and photophysical deactivation. -Sunzmary. In t h e prcx-ious paper 111 the structure of t h e iiitcrmcdiatc in t h e photochemical iiidazole-bcnzimidazole-isom~rization was discussed (3 in Schrzize I ) . I n llrrs coniinunication experiments concerning t h e pho-tochcniical primary proc s and 1)liotupliysicd dcactivatioii of 2-alkyl-indazolcs (1) are c1escril)cd. Tlic In dcr vorliegendcn ,4rhcit bcriclitcii wir ubei-detaillie1 tc Stut1it.n zuni L)e5ahti-\iierungsverlialten von 2-Alkyl-indazolen und Lutn Verlauf tler pliotcic lieniiscllcn €'rirnirreaktion 1 --f 3. Die3e Untersucliungen wurdcn vorwiegeud an 2,3-Dimetliylindazol vorgenoinmen, docli zeigen alle 2-Alliyl-indazole, die sich photot hemisch in 1-Alkyl-benzimidazole umwandeln lassen, qualitativ dasselbe Verhalten. Quantitative Messungeii wurden zudern an drei Indazolen durcligefuhrt, die dieie Reaktiori nicht Leigen (vgl. Tabelle 1).

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Zum Mechanismus der photochemischen Umwandlung von 2‐Alkyl‐indazolen in 1‐Alkyl‐benzimidazole. II. Photophysikalische und photochemische Primärprozesse

Heinzelmann

Märky

Gilgen

1976

Helvetica Chimica Acta

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Obituary

Wagnière¹

1978

Helvetica Chimica Acta

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Zur strahlungslosen Desaktivierung des tiefsten angeregten Singulett‐Zustandes von 2‐Alkyl‐indazolen in neutraler und protonierter Form

Heinzelmann

1978

Helvetica Chimica Acta

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SummaryThe temperature dependence of the quantum yields of fluorescence (QF), intersystem crossing (aT) and photoreactions (@ R) have been measured for several neutral and protonated 2-alkyl-indazoles. The experimental data ( Fig. 1 and 3) can be interpreted in terms of the reaction schemes I and 2 with temperature independent constants for fluorescence emission and intersystem crossing and temperature dependent photochemical primary processes. Whereas at low temperatures the sum of the quantum yields of fluorescence and intersystem crossing equals 1, at higher temperatures a very efficient radiationless deactivation process takes place (Table). Based on kinetic and photochemical data it is concluded that this deactivation proceeds via a hypersurface crossing (Fig. 2) or hypersurface touching (Fig. 4) in the course of the photochemical rearrangements 1 + 2 and 4 + 5 respectively.Similar mechanisms are expected to be responsible for the unusual internal conversion in other heterocyclic compounds.

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Temperature dependence of the deactivation of electronically excited indazoles in solution

Cited by 6 publications

References 25 publications

Zum Mechanismus der photochemischen Umwandlung von 2‐Alkyl‐indazolen in 1‐Alkyl‐benzimidazole. II. Photophysikalische und photochemische Primärprozesse

Zum Mechanismus der photochemischen Umwandlung von 2‐Alkyl‐indazolen in 1‐Alkyl‐benzimidazole. II. Photophysikalische und photochemische Primärprozesse

Obituary

Zur strahlungslosen Desaktivierung des tiefsten angeregten Singulett‐Zustandes von 2‐Alkyl‐indazolen in neutraler und protonierter Form

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