Dynamics of Intramolecular Excited State Proton Transfer in Emission Tunable, Highly Luminescent Imidazole Derivatives

Abstract

The enol–keto excited state dynamics of a series of emission tunable imidazole derivatives undergoing excited state intramolecular proton transfer (ESIPT) were determined by means of steady state and time-resolved spectroscopic techniques in different solvents at room temperature and at 77 K. Examination of the corresponding non-ESIPT compounds, with the proton transfer function deliberately blocked, was carried out for comparison. At room temperature, the ESIPT process in the examined samples, determined by picosecond streak camera experiments, had lifetimes ranging from less than 10 ps to ca. 100 ps, and the resulting keto forms deactivated with lifetimes less than 100 ps up to a few nanoseconds. Delayed luminescence detection at 77 K in solid glasses allowed the identification of the phosphorescence of the enolic form and, in a few cases, P-type delayed fluorescence was also seen. The phosphorescence lifetimes were in the range of seconds at 77 K. The enolic triplet excited state absorption at RT, determined by nanosecond laser flash-photolysis, displayed a maximum around 460–500 nm and lifetimes on the order of tens of microseconds. In a few cases, a broad band with a maximum around 420 nm was detected and tentatively ascribed to the triplet excited state of the keto form. Reaction rates with oxygen on the order of (2–4) × 109 M–1 s–1 were measured.

Synthesis, crystal structure and DFT studies of a dual fluorescent ketamine: Structural changes in the ground and excited states

“…In the excited state the proton may be transferred from amine group (NH) to keto group (C=O) through ESIPT process leads to the existence of both KHB and EHB forms [18][19][20][21][22][23]33]. In dual emission, the low intensity peak at 410 nm arises from the normal ketamine form and the red shifted high intensity peak at 435 nm corresponds to the stable tautomeric enolimine form.…”

“…This hypothesis leads to the concept of twisted intramolecular charge transfer (TICT) process. A number of reports have shown that the degree of steric hindrance plays an important role in dual emission arises from twisted intramolecular charge transfer (TICT) or excited state intramolecular proton transfer (ESIPT) process [18][19][20][21][22][23].…”

Catalytic‐Type Excited‐State N−H Proton‐Transfer Reaction in 7‐Aminoquinoline and Its Derivatives

“…In this study, for generalization, we lift the boundary of the unimolecular‐type ESIPT and extend the research to systems in which the proton donor (‐NHR) and acceptor are greatly separated, precluding the formation of an intramolecular H‐bond. Therefore, the occurrence of excited‐state proton transfer (ESPT), if available, requires the assistance of surrounding solvent molecules .…”

Photochromic Properties of Novel One‐pot Multicomponent Synthesized Tetraarylimidazoles

“…The imidazole nucleus is a key building block that has been extensively used in anion sensors, ionic liquids, as well as electronic and optical materials . Triphenylimidazoles played an important role in the discovery of chemiluminescence, for this purpose tetraarylimidazoles have recently attracted significant interest . Nevertheless, the effects of substituent groups on the imidazole ring on the photochromic properties are not clear.…”