Excited-State Intramolecular Proton Transfer Molecules Bearing o-Hydroxy Analogues of Green Fluorescent Protein Chromophore

Abstract

o-Hydroxy analogues, 1a-g, of the green fluorescent protein chromophore have been synthesized. Their structures and electronic properties were investigated by X-ray single-crystal analyses, electrochemistry, and luminescence properties. In solid and nonpolar solvents 1a-g exist mainly as Z conformers that possess a seven-membered-ring hydrogen bond and undergo excited-state intramolecular proton transfer (ESIPT) reactions, resulting in a proton-transfer tautomer emission. Fluorescence upconversion dynamics have revealed a coherent type of ESIPT, followed by a fast vibrational/solvent relaxation (<1 ps) to a twisted (regarding exo-C(5)-C(4)-C(3) bonds) conformation, from which a fast population decay of a few to several tens of picoseconds was resolved in cyclohexane. Accordingly, the proton-transfer tautomer emission intensity is moderate (0.08 in 1e) to weak (∼10(-4) in 1a) in cyclohexane. The stronger intramolecular hydrogen bonding in 1g suppresses the rotation of the aryl-alkene bond, resulting in a high yield of tautomer emission (Φ(f) ≈ 0.2). In the solid state, due to the inhibition of exo-C(5)-C(4)-C(3) rotation, intense tautomer emission with a quantum yield of 0.1-0.9 was obtained for 1a-g. Depending on the electronic donor or acceptor strength of the substituent in either the HOMO or LUMO site, a broad tuning range of the emission from 560 (1g) to 670 nm (1a) has been achieved.

Synthesis, X-ray Structure, Spectroscopic Properties and DFT Studies of a Novel Schiff Base

“…, a large Stokes shifted S 1 (K *)→S 0 (K) fluorescence. This unusual optical property has found many important applications, including probes for solvation dynamics [57] and biological environments [58], photochromic materials [59], chemosensors [60,61,62,63,64], and organic light-emitting diodes [65,66,67]. In addition, many relevant examples have recently been examined by anchoring the ESIPT molecules with a strong electron-donating group (dialkylamino group), so that upon Franck-Condon excitation, excited-state intramolecular charge transfer (ESICT) may take place [68].…”

Role of Solvation Dynamics in Excited State Proton Transfer of 1‐Naphthol in Nanoscopic Water Clusters Formed in a Hydrophobic Solvent

“…Hydrogen bonding interaction and associated intramolecular processes like proton transfer in biomolecules following photoexcitation is of fundamental importance in modern chemistry and has received significant attention in recent time (1,2). In the past years, the hydrogen bonding effects on the structures and dynamics of many important molecular systems have been well investigated (3)(4)(5)(6)(7)(8)(9)(10)(11).…”

Fluorophores for Excited‐State Intramolecular Proton Transfer by an Yttrium Triflate Catalyzed Reaction of Isocyanides with Thiocarboxylic Acids

“…Upon UV excitation, compound 1a emitted fluorescence in purple to blue region. [19] Inserting am ultiple bond between the two aromatic rings (1t, 1w)l ed to further red shifts,with 1t emitting in the yellow region ( Figure 1). Enlarging the conjugate system as in 1s-1whas the same effect (76.8 %for 1v).…”