Excited-state Proton Transfer of 2-(2-Hydroxyphenyl)benzothiazole in the Confined Nanocavity†

doi:10.7503/cjcu20141071

Abstract

Abstract:

Proton transfer as one of the basic reaction exists in a large variety of chemical and biochemical process. And the organic molecules that exist the proton transfer process offten existence potential applications in biological and chemical industry. In this work, the supramolecular interaction of 2-(2-hydroxyphenyl)benzothiazole(HBT) with different concentrations cucurbit[7]uril(CB7) and its influences on the exited state intramolecular proton transfer(ESIPT) of HBT were studied with stead-state and transient fluorescence spectra in the different solvents. Furthermore, the inclusion ratio of CB7 and HBT were obtained according to Benesi-Hildebrand equation based on the fluorescence data. The results show that the stoichiometric ratio 1:1 host-guest complex of CB7 with HBT is formed in the N,N-dimethyeformamide(DMF) or dichloromethane solution, and the proton transfer of HBT is very sensitive to solvent. When the concentration of CB7 was increased, the fluorescence lifetime and quantum yield of HBT were decreased and increased respectively. The phenolic oxygen negative ion was formed in DMF, and the ESIPT of HBT was decreased in dichloromethane. The quantum chemical calculations show that CB7 can form the 1:1 HBT@CB7 complexes for the enol or keto tautomer of HBT.

Key words: 2-(2-Hydroxyphenyl)benzothiazole, Cucurbit[7]uril, Proton transfer, Fluorescence spectrum, Quantum chemical calculation

CLC Number:

TrendMD:

XIANG Junfeng, YI Pinggui, YU Xianyong, CHEN Jian, HAO Yanlei, REN Zhiyong. Excited-state Proton Transfer of 2-(2-Hydroxyphenyl)benzothiazole in the Confined Nanocavity^†[J]. Chem. J. Chinese Universities, 2015, 36(4): 654.

Figures/Tables 7

Fig.1 Structure of CB7 and proton transfer process of HBT

Fig.2 Fluorescence spectra of HBT in different solvents (A) a. DMSO, b. DMF, c. ethanol, d. THF; (B) a. hexamethylene, b. dioxane, c. dichloromethane, d. ethylacetate.

Fig.3 Fluorescence spectra of HBT with different CB7 concentrations in DMF(A) and dicholormethane(B)

Fig.4 Benesi-Hildebrand plots of HBT with CB7 in DMF(a) and dicholormethane(b) (A) Eq.(1); (B) Eq.(2).

Table 1 Fluorescence lifetime evaluated for HBT-CB7 complexes*

V(CB7)/μL	λ_em/nm	Lifetime/ns		Amplitude(%)		$χ red 2$	Mean lifetime/ns
V(CB7)/μL	λ_em/nm	τ₁	τ₂			α₁	α₂
0	409	0.80	2.31	76.77	23.24	0.982	1.51
	466	4.12	17.05	99.33	0.67	1.070	4.47
10	409	0.82	2.50	83.22	16.78	1.014	1.46
	466	2.66	4.29	9.98	90.02	1.081	4.19
20	409	0.81	2.39	84.82	15.18	1.017	1.36
	466	2.34	4.31	11.62	88.38	0.920	4.18
30	409	0.86	2.49	88.10	11.90	1.046	1.32
	466	1.85	4.22	6.22	93.78	0.986	4.15
40	409	0.81	2.43	87.05	12.95	1.043	1.31
	466	1.95	4.19	4.34	95.66	0.908	4.14
50	409	0.77	2.33	85.32	14.68	0.944	1.30
	466	1.91	4.20	5.32	94.68	0.991	4.14
60	409	0.82	2.64	90.01	9.99	1.044	1.30
	466	1.82	4.20	7.85	92.15	0.973	4.12
70	409	0.85	2.74	91.64	8.36	1.103	1.28
	466	1.44	4.15	4.44	95.56	1.078	4.11
80	409	0.85	2.59	91.25	8.75	1.093	1.24
	466	1.23	4.10	2.32	97.68	1.085	4.08

Table 1 Fluorescence lifetime evaluated for HBT-CB7 complexes*

V(CB7)/μL	λ_em/nm	Lifetime/ns		Amplitude(%)		$χ red 2$	Mean lifetime/ns
V(CB7)/μL	λ_em/nm	τ₁	τ₂			α₁	α₂
0	409	0.80	2.31	76.77	23.24	0.982	1.51
	466	4.12	17.05	99.33	0.67	1.070	4.47
10	409	0.82	2.50	83.22	16.78	1.014	1.46
	466	2.66	4.29	9.98	90.02	1.081	4.19
20	409	0.81	2.39	84.82	15.18	1.017	1.36
	466	2.34	4.31	11.62	88.38	0.920	4.18
30	409	0.86	2.49	88.10	11.90	1.046	1.32
	466	1.85	4.22	6.22	93.78	0.986	4.15
40	409	0.81	2.43	87.05	12.95	1.043	1.31
	466	1.95	4.19	4.34	95.66	0.908	4.14
50	409	0.77	2.33	85.32	14.68	0.944	1.30
	466	1.91	4.20	5.32	94.68	0.991	4.14
60	409	0.82	2.64	90.01	9.99	1.044	1.30
	466	1.82	4.20	7.85	92.15	0.973	4.12
70	409	0.85	2.74	91.64	8.36	1.103	1.28
	466	1.44	4.15	4.44	95.56	1.078	4.11
80	409	0.85	2.59	91.25	8.75	1.093	1.24
	466	1.23	4.10	2.32	97.68	1.085	4.08

Fig.5 Fluorescence spectra of HBT-CB7 complexes(A) and quantum yield(B) in DMSO

Fig.6 Computationally optimized structures for HBT and CB7 systems (A) HBT(enol)@CB7; (B) HBT(keto)@CB7

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