Tuning the Solution Phase Photophysics of Two De Novo Designed Hydrogen Bond Sensitive 9-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one Derivatives

Abstract

Two new fluorophores, 6,7-dimethoxy-9-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one (DMTCO) and 5-methyl-8,9-dihydro-5H-[1,3]dioxolo[4,5-b]carbazol-6(7H)-one (MDDCO), first of their kind, have been synthesized from the corresponding methoxy and methylenedioxy derivatives of 2,3,4,9-tetrahydro-1H-carbazol-1-one respectively. Comprehensive photophysical characterization of these compounds has been carried out in sixteen different homogeneous solvents and binary solvent mixtures. Both of these compounds are sensitive to solvent polarity, but the sensitivity is much higher in electronic excited state observed by steady-state and time-resolved fluorescence experiments than in ground state studied by UV-vis absorption spectroscopy. The fluorescence spectral shifts are linearly correlated with the empirical parameters of the protic solvents and also the quantitative influence of the empirical solvent parameters on the emission maxima of the compounds has been calculated. The change in dipole moment of the compounds in their excited state has been calculated from the shifts in corresponding emission maxima in pure solvents. A higher dipole moment change of both DMTCO and MDDCO in protic solvents is due to intermolecular hydrogen bonding which is further confirmed by the comparison of their behaviour in toluene-acetonitrile and toluene-methanol solvent mixtures. From structural features, MDDCO is more planar compared to DMTCO, which is reflected better in fluorescence quenching of the former with organic bases, N,N-dimethylaniline and N,N-diethylaniline. Laser flash photolysis experiments prove that the quenching interaction originates from photoinduced electron transfer from the bases to the compounds.

Influence of microheterogeneity on the solution phase photophysics of a newly synthesised, environment sensitive fluorophore 2-((7,8-dimethyl-1-oxo-2,3,4,9-tetrahydro-1H-carbazol-6-yl)oxy)acetic acid and its tagged derivative

“…There is also possibility for specific H-bonding interactions with the surrounding solvent as the compounds contain hetero atoms that are potential sites for the formation of hydrogen bonds. It has been reported already that such molecules are keen to form hydrogen bonds in the electronic excited state with the surrounding solvent molecules [9], [11]. The quantitative influence of the hydrogen bond donor and acceptor ability of a solvent on the excited state photophysics of both DOTHCA and EDOTHCAB has been calculated later in Section 3.4.…”

“…In the last few communications, we have reported methoxy derivatives of 1-keto-1,2,3,4-tetrahydrocarbazole as environment sensitive fluorophores [8][9][10][11][12]. Fluorescence emission of those derivatives got positioned in different regions of the spectrum owing to significant changes in dipole moment in excited state in addition to the formation of hydrogen bonds with the surrounding solvent molecules.…”

Solution phase photophysics of 5,7-dimethoxy-2,3,4,9-tetrahydro-1H-carbazol-1-one: Analysing the lineaments of a new fluorosensor to probe different micro-environments

“…However, no such trend, depending on a particular solvent parameter, is observed in the case of protic solvents. When it comes to long chain alcohols, fluorescence decay profiles are better fitted in a bi-exponential decay equation as KTHC-57 is differentially solvated to polar head groups and the hydrophobic tail regions of such alcohols [39,40]. FWHM of the excitation pulse used in this experiment is 0.3 ns and the lifetime of one of the components is approximately close to the 0.3 ns.…”

Photophysics of a solvent sensitive keto-tetrahydrocarbazole based fluorophore and its interaction with triethylamine: A spectroscopic inquest under surfactant and β-CD confinement

“…Solvent sensitive small molecule fluorophores are precious owing to their capability to probe micro-environments which can decipher bulk information in the study of molecular biology, drug discovery, material science, tissue diagnostics, environmental indicators, enzyme substrates and cellular staining agents [2]. Recently, new heterocyclic fluorophores like methoxy derivatives of keto-tetrahydrocarbazole [3][4][5] have earned increasing interest because of their distinctive ability to sense the nature of their surrounding medium. These fluorophores are particularly responsive to the hydrogen bonding nature of the solvent [3][4][5].…”

“…Recently, new heterocyclic fluorophores like methoxy derivatives of keto-tetrahydrocarbazole [3][4][5] have earned increasing interest because of their distinctive ability to sense the nature of their surrounding medium. These fluorophores are particularly responsive to the hydrogen bonding nature of the solvent [3][4][5]. Nevertheless, polarity of the solvent molecules also plays an influential role in controlling the position of emission maxima of these fluorophores [3,5].…”