title: Stimuli-sensitive breathing of Cucurbit[7]uril cavity: monitoring through the environment responsive fluorescence of 1'-hydroxy-2'-acetonaphthone (HAN).
abstract: In this work, we have focused on the supramolecular interactions of a water-soluble host Cucurbit[7]uril (CB[7]) with an excited state intramolecular proton transfer (ESIPT) probe 1'-hydroxy-2'-acetonaphthone (HAN) through steady-state and time-resolved fluorescence measurements. In water HAN is almost nonfluorescent in nature with a very low fluorescence quantum yield (Φ = 0.009). With gradual addition of CB[7] absorption maximum of HAN is red-shifted (292 cm(-1)) and hence confirming the formation of an inclusion complex in the ground state between HAN and CB[7]. Due to this complexation CB[7] offers a hydrophobic microenvironment to the HAN which is completely different from that of homogeneous water. Upon encapsulation into the nanocavity of CB[7], HAN exhibits a 20-fold increase in fluorescence intensity along with a 36 nm (1618 cm(-1)) hypsochromic shift in emission maxima. This hypsochromic shift is an indication about the modulation of excited state photophysical behavior of HAN due to the formation of HAN-CB[7] inclusion complex. Moreover, huge partition coefficient of HAN from water to CB[7] along with a∼ 12-fold increase in fluorescence lifetime confirm the favorable interaction between HAN and CB[7]. We have also observed the stimuli-sensitive (temperature and cationic stimuli) breathing of CB[7] cavity i.e., in the presence of different additives the portals of CB[7] open up to release HAN in water and take up the additives. Time-resolved anisotropy measurements further indicate about the probable location of HAN inside the CB[7]. The observation of a 1.7 ns component in the presence of CB[7] signifies the highly restricted rotational motion of HAN inside the cavity of CB[7] corroborates our finding.
authors.affiliation: Department of Chemistry, Indian Institute of Technology , Kharagpur 721302, WB, India.
authors.forename: Debasis
authors.initials: D
authors.lastname: Banik
authors.forename: Jagannath
authors.initials: J
authors.lastname: Kuchlyan
authors.forename: Arpita
authors.initials: A
authors.lastname: Roy
authors.forename: Niloy
authors.initials: N
authors.lastname: Kundu
authors.forename: Nilmoni
authors.initials: N
authors.lastname: Sarkar
mesh_terms: D065966:Absorption, Physicochemical; D001952:Bridged-Ring Compounds / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry; D005454:Fluorescence Polarization; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry; D009284:Naphthols / Q000737:chemistry*; D012964:Sodium / Q000737:chemistry; D013696:Temperature; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils
chemical_list: D001952:Bridged-Ring Compounds; D002118:Calcium; D007093:Imidazoles; D052578:Ionic Liquids; D009284:Naphthols; D012964:Sodium; C000605265:1'-hydroxy-2'-acetonaphthone; C456276:cucurbit(7)uril; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils