TY - JOUR
T1 - The Effect of Pyrazolyl Substituents on the Photophysical and Photochemical Properties of Pyrazine Derivatives
AU - Pizarro, Nancy
AU - Prado, Gaspar
AU - Saldías, Marianela
AU - Sandoval-Altamirano, Catalina
AU - Vega, Andrés
N1 - Funding Information:
Acknowledgements—The authors gratefully acknowledge partial financial support of Comisión Nacional Científica y Tecnológica, grants FONDECYT 1160546, 1160749, 3170100, ACT-1404 (IPMaG), FONDEQUIP EQM 160099 and Financiamiento Basal para Centros Científicos y Tecnológicos de Excelencia FB0807.
PY - 2018/1/1
Y1 - 2018/1/1
N2 - The reaction of 2,5-dibromopyrazine with N-Lithium pyrazolate in a 1:2 ratio leads to a mixture of 2-bromo-5-(1H-pyrazol-1-yl)pyrazine (I) and 2,5-di(1H-pyrazol-1-yl)pyrazine (II). The structures of I and II are highly planar. Two absorption bands can be observed for the compounds in the UV-Vis region, having ε in the order of 104 m-1 cm-1. TD-DFT computed results support the nature of the lower energy absorptions as πpyrazine→π*pyrazine transitions, including an additional intraligand charge transfer transition for I (πpyrazol→π*pyrazine). Upon excitation at 280 or 320 nm, the emission of both compounds is almost not affected by solvent polarity or oxygen presence, showing two bands for I and one for II in the 350-450 nm region. Emission of II follows a mono-exponential decay, while I decays following a bi-exponential law, hypothesized from πpyrazine→π*pyrazine and πpyrazol→π*pyrazine transitions. Photodegradation of I and II follows a first-order kinetic with constants of 1.18 × 10-2 min-1 and 0.13 × 10-2 min-1, respectively. Results suggest that photodegradation of I starts with the loose of bromide followed by intermolecular pyrazolyl subtraction and ring opening. This path is not available for II, which is reflected in its enhanced photostability.
AB - The reaction of 2,5-dibromopyrazine with N-Lithium pyrazolate in a 1:2 ratio leads to a mixture of 2-bromo-5-(1H-pyrazol-1-yl)pyrazine (I) and 2,5-di(1H-pyrazol-1-yl)pyrazine (II). The structures of I and II are highly planar. Two absorption bands can be observed for the compounds in the UV-Vis region, having ε in the order of 104 m-1 cm-1. TD-DFT computed results support the nature of the lower energy absorptions as πpyrazine→π*pyrazine transitions, including an additional intraligand charge transfer transition for I (πpyrazol→π*pyrazine). Upon excitation at 280 or 320 nm, the emission of both compounds is almost not affected by solvent polarity or oxygen presence, showing two bands for I and one for II in the 350-450 nm region. Emission of II follows a mono-exponential decay, while I decays following a bi-exponential law, hypothesized from πpyrazine→π*pyrazine and πpyrazol→π*pyrazine transitions. Photodegradation of I and II follows a first-order kinetic with constants of 1.18 × 10-2 min-1 and 0.13 × 10-2 min-1, respectively. Results suggest that photodegradation of I starts with the loose of bromide followed by intermolecular pyrazolyl subtraction and ring opening. This path is not available for II, which is reflected in its enhanced photostability.
UR - http://www.scopus.com/inward/record.url?scp=85047489417&partnerID=8YFLogxK
U2 - 10.1111/php.12911
DO - 10.1111/php.12911
M3 - Article
AN - SCOPUS:85047489417
SN - 0031-8655
VL - 94
SP - 845
EP - 852
JO - Photochemistry and Photobiology
JF - Photochemistry and Photobiology
IS - 5
ER -