Study On Light-regulated Intramolecular Torsional Charge Transfer (TICT) And Host-guest Fluorescence Phenomena Of Cucurbit Rin

Light-emitting materials with tunable properties may offer fascinating applications in optoelectronic devices,fluorescent sensors,and imaging agents.Due to their long-range tunable luminescent capabilities,D-π-A molecules exhibiting intramolecular charge transfer（ICT）luminescence have attracted a lot of attention.Even so,there are still few reports on the fluorescence characteristics of ICT and TICT of D-π-A⁺type molecules with greater water solubility.D-π-A⁺’s fluorescence properties are very different from those of typical neutral molecules（D-π-A）without charge since it possesses one unit of positive charge.In this study,eight different types of D-π-A⁺TICT molecules are developed and created.Alkylated pyridonium ion makes up the electron acceptor Part（A）,whereas the electron donor Part（D）is made up of an aromatic ring with strongπ-conjugated characteristics.We select the benzene ring as the bridge based on its features that are rotationally changeable.The ICT and TICT properties of these D-π-A⁺bipyridine molecules were then examined,along with the cucurbituril host-guest interaction and the ICT luminescence features of TICT molecules.Chapter 1:Intramolecular charge transfer（ICT）phenomenon,twisted intramolecular charge transfer（TICT）,several well-known TICT compounds,and various TICT control techniques are reviewed in Chapter 1.Lastly,a brief introduction to the pertinent material in the topic of host-guest ICT fluorescence regulation in cucurbiturils is made.Chapter 2:A number of anthracene phenyl pyridine compounds were synthesized.The hyperconjugation between alkyl moiety on pyridine was studies by¹H NMR spectroscopy.By comparing fluorescence spectra of solvation and fluorescence spectra at various temperatures,the effects of ICT and TICT in low polarity solvents were confirmed.It was discovered that after being exposed to UV light of various wavelengths for a while,the fluorescence emission spectrum of anthracene-phenylpyridine in dichloromethane solution will either be red-shifted or blue-shifted.Theoretical study and ¹H NMR spectra supported the theory that this phenomena was brought on by varying degrees of molecule twisting during illumination.The TICT impact of light regulation was therefore postulated.It was also discovered that the short wavelength LE fluorescence is produced by the D-π-A⁺molecule after TICT torsion due to the conjugation effect of donor part D,which is known as LE state emission induced by TICT torsion,because of theπ-conjugation property of the anthracene ring itself.Chapter 3:Due to the aqueous solvent’s solvation,the double-emitting anthracene-phenylpyridine G1 in aqueous solution can only fluoresce at short wavelengths in blue.However,following their interaction,Q[8]and G1 produced a supramolecular complex that considerably red-shifted G1’s fluorescence emission,with a stokes shift up to 185 nm in comparison to free emission.NMR and MS results supported the finding that Q[8]with G1 formed supramolecular complexes with 1:2and 2:2 structures.Theoretical study shown that the guest molecule’s ICT excited state has a relatively lower dipole moment than the LE excited state,making it less stable under the influence of water polarization.With the presence of the guest molecule,the hydrophobic cavity of Q[8]can effectively form a shield under the influence of water polarity.As a result,guest molecules have significantly increased ICT excited state stability.The fluorescence of guest molecules is therefore red-shifted from blue to cyan and eventually to red under the interaction of Q[8].Chapter 4:The interaction of anthracene with dichromate in aqueous solution suppressed the fluorescence emission of anthracene biphenyl pyridine.It was discovered that other common anions had no effect on the quenching of anthracene-bipyridine’s fluorescence emission,and even a modest quantity of dichromate anion may do so.In order to detect Cr₂O₇^2-in aqueous solution,anthracpyridine G1,G2,G3,and G4 were developed as fluorescent probes.According to the theoretical analysis,Gr₂O₇^2-has a low HOMO energy level can accept the excited electron from probe.Due to intermolecular charge transfer（CT）,which results in the probe molecule’s fluorescence being quenched,the HOMO electron of the probe is now easily caught by the Gr₂O₇^2-that is nearby after being photoexcited.Chapter 5:Based on research on anthracene-phenylpyridine,we converted the anthracene ring to a naphthalene ring and a number of positive-charged D-π-A⁺cations of naphthalene-phenylpyridine were synthesized.We then compared the characteristics of phenylpyridine produced at various substitution positions on the naphthalene ring.It was discovered that,in comparison to anthracene-phenylpyridine,naphthalene-biphenylpyridine displayed a certain degree of predistortion due to steric hindrance effect,and that this predistortion of the benzene ring and naphthalene ring could increase the stability of the ICT excited state.Thus,the naphthylpyridine which LE state emission peak quenched in aqueous solution at the same conditions of the same alkyl chain length and different positions substituted naphthylpyridine molecules,and revealed a faint ICT state emission.The photoregulatory TICT phenomenon was also confirmed in 1,4-dioxane solution at the same time.While the fluorescence wavelength continued to show a blue shift under 365 nm UV irradiation,unlike anthracylpyridine,naphthylpyridine produced near white light emission under254nm UV irradiation.The lengthy carbon chain naphthalene-biphenylpyridine G6 at the substitution site is a good example of this occurrence.It issuggested that the carbon chain’s expansion may boost the ICT effect,whereas the tiny substitution site’s steric barrier facilitates torsion.Chapter 6:We studied Q[7],Q[8],and TMe Q[6]how affected the ICT luminous effects of naphthalene biphenyl-pyridinecations.It has been discovered that cucurbiturils can significantly increase the ICT luminescence intensity of naphthylpyridine guests with large pre-twisted dihedral Angle and long carbon chains.At the same time,guest molecules can form a dimer with an overlapping head and tail because of the 1:2 and 2:2 inclusion complexes that are assemblied by Q[8]and guest molecules.Due to"π-π"stacking,this dimer can quench the LE state luminescence of guest molecules but has no impact ICT state emission.The modest effect of TMe Q[6]on ICT emission enhancement is caused by the small cavity,which only allows it to bind the carbon chain part of the guest molecule when it interacts with the host-guest.Chapter 7:This part presents a methodical summary by summary of the research findings.The dual emission properties of the biphenylpyridine D-π-A⁺structural morphoid molecule include the ICT state and the LE state,and the ICT state’s dipole moment is significantly smaller than the LE state’s.This causes the ICT state emission inlow polar solvents,and the ICT effect is what causes TICT torsion.By irradiation UV rays of various wavelengths,the torsion of TICT may be controlled.Moreover,it is discovered that the presence of TICT phenomenon does not always result in the quenching of ICT fluorescence.After torsion,TICT molecules can emit short-wavelength LE state blue light because of the conjugation property of the aromatic ring of electron donor（D）,which forms the basis for photoregulating TICT dual emission luminescence.The ICT effect of guest molecules,which can only emit blue light in aqueous solution,is considerably improved after being enclosed by the cucurbiturils cavity,emitting long wavelength emission,based on the shielding effect of hydrophobic cavities of cucurbiturils in the polarity of water.Moreover,the length of the alkyl carbon chain,the hyperconjugation of the carbon chain with pyridine ring,the pre-distortion of the aryl donor structure,andπ-πstacking all significantly affect the fluorescence emission of the host-guest fluorescence molecules of the D-π-A⁺structure.These study findings provides more guidance for the creation of controllable multi-color host-guest fluorescent materials.