First 1-hydroxy-1H-imidazole-based ESIPT emitter with an O–H⋯O intramolecular hydrogen bond: ESIPT-triggered TICT and speciation in solution

Abstract

Search for new types of ESIPT-capable molecules is crucial for understanding factors controlling the ESIPT photoreaction. In this paper we present combined experimental and theoretical studies of the proton transfer...

ESIPT-Capable 4-(2-Hydroxyphenyl)-2-(Pyridin-2-yl)-1H-Imidazoles with Single and Double Proton Transfer: Synthesis, Selective Reduction of the Imidazolic OH Group and Luminescence

“…A non-constrained geometry optimization of the S 1 state directly leads to a non-planar geometry near the conical intersection (CI) between the S 0 and S 1 states ( Figure 9 b). According to the literature, ESIPT is often coupled with the radiationless deactivation via twisted intramolecular charge transfer (TICT) states of a non-planar biradicaloid nature [ 83 , 85 , 94 , 95 , 96 , 97 , 98 , 99 ]. This non-planarity arises from the twisting around a double-like bond between proton-donating and proton-accepting moieties (around the C Ph –C Imid bond in our case).…”

“…The quantum chemical calculations presented in this study were conducted using density functional theory (DFT), time-dependent DFT (TDDFT) and Tamm–Dancoff approximated DFT (TDADFT) methods in Gaussian 16 software package [ 103 ]. We used the hybrid exchange-correlation functional PBE0 [ 104 ] since our previous studies demonstrated its satisfying performance in modeling photophysical and photochemical properties of organic ESIPT-emitters [ 83 , 85 ]. Compared with probably the best known hybrid functional B3LYP, PBE0 provides absorption energies that are closer to the experimental data, while B3LYP tends to red-shift some vertical absorptions for L H,OH and L OH,OH ( Supplementary Materials , Figures S12 and S13 ).…”

“…Normally, when decorated with such proton-donating groups as unsubstituted or substituted 2-hydroxyphenyl groups in the α-position to aza-atoms, their free nitrogen atoms act as proton acceptors during the ESIPT process [ 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 ]. Recently we proposed a new approach in the design of imidazole-based ESIPT-fluorophores in which we switched the role of the imidazole cycle to the one of a proton donor by introducing the hydroxy group in the position 1 and the pyridin-2-yl group in the position 2 of the imidazole ring [ 83 , 84 , 85 , 86 , 87 ]. Importantly, both roles of the imidazole ring in ESIPT-fluorophores, i.e., the proton acceptor and the proton donor ones, can be combined in a single molecule if we introduce the proton-donating 2-hydroxyphenyl group in the position 4 and the proton accepting pyridin-2-yl group in the position 2 of the 1-hydroxy-1 H -imidazole moiety.…”

Luminescence of ESIPT-capable zinc(ii) complexes with a 1-hydroxy-1H-imidazole-based ligand: exploring the impact of substitution in the proton-donating moiety

“…The emission of ESIPT-capable dyes is highly sensitive to solvents, 43–50 substitution in the ESIPT-dye core, 51–71 protonation/deprotonation, 72–80 and coordination of metal ions. 81–96 Normally, the latter process is coupled with the deprotonation of ESIPT-dyes.…”

“…[32][33][34][35][36][37][38][39][40][41] This plethora of emissive excited states makes ESIPT-capable compounds an appealing platform for the design of multicolor luminescent materials. 42 The emission of ESIPT-capable dyes is highly sensitive to solvents, [43][44][45][46][47][48][49][50] substitution in the ESIPT-dye core, protonation/deprotonation, [72][73][74][75][76][77][78][79][80] and coordination of metal ions. [81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96] Normally, the latter process is coupled with the deprotonation of ESIPT-dyes.…”