Resonance raman and absorption studies of the configurations of photochromic 3-alkyl-substituted 1,5-diphenylformazans: steric effect of the substituent

Monitoring the photochemistry of a formazan over 15 orders of magnitude in time

“…The photochemistry of the precursor TTC has already been explored in detail with various techniques ( Pechmann and Runge, 1894 ; Hausser et al, 1949b ; Nineham, 1955 ; Neugebauer and Russell, 1968 ; Umemoto, 1985 ; Gonzalez and San Roman, 1989 ; Kovács et al, 1996 ; Kanal et al, 2015 ; Bolze et al, 2018 ). Despite several studies with a focus on quantum-chemical calculations ( Buemi et al, 1998 ; Buemi and Zuccarello, 2002 ; King and Murrin, 2004 ; Tezcan and Tokay, 2010 ; Sherif, 2015 ), luminescence ( Turkoglu et al, 2015 ), solvatochromism ( Sherif, 1997 ; Kumar et al, 2014 ; Wortmann et al, 2022 ), Raman and infrared studies ( Schiele, 1965 ; Otting and Neugebauer, 1968 ; Otting and Neugebauer, 1969 ; Lewis and Sandorfy, 1983 ; Hiura and Takahashi, 1989a ; Hiura and Takahashi, 1989b ; Tezcan and Ozkan, 2003 ), or electrochemical properties ( Gökçe et al, 2005 ; Sherif, 2015 ; Turkoglu et al, 2015 ) of formazans, also investigated under temperature ( Kuhn and Weitz, 1953 ; Langbein, 1979 ; Grummt and Langbein, 1981 ; Sueishi and Nishimura, 1983 ) or pressure variation ( Sueishi and Nishimura, 1983 ), the interplay of light-induced processes which set in on an ultrafast time scale and extend to minutes has not been comprehensively studied for TPF. With regard to the involved intermediate species of TPF, several photoisomerization mechanisms of TPF are discussed in literature, with the one proposed by Grummt and Langbein which was derived from laser flash photolysis experiments ( Grummt and Langbein, 1981 ) being in closest accordance to the one inferred in our recent study ( Wortmann et al, 2022 ).…”