Aindrila Sarkar

A study on the spectroscopy and photophysics of N-phenyl pyrrole and N-phenyl pyrazole

Abstract Comprehensive spectroscopic and photophysical studies of N-phenyl pyrrole (PPr) and N-phenyl pyrazole (PPz) in different solvents show that a new emission band appears due to aggregation of PPr in water. The presence of β-cyclodextrin (β-CD) in aqueous solution of PPr causes deaggregation but the twisted intramolecular charge transfer emission ceases due to the cavity effect. In PPz, aggregation and TICT emission are absent. Protonation in PPz is restricted to a single site only at very high acid concentration. Both the molecules are planar in the ground state.

Photophysics of phenyl pyridines and bipyridines in different media

Abstract Analysis of absorption and emission spectra of 2,4′-bipyridine (2BPy), 4,4′-bipyridine (4BPy) and three isomeric phenyl pyridines (PhPy) in different solvents reveal that the general nature of lowest emitting state is π, π∗. A significant enhancement of fluorescence of 2PhPy at 77 K in relation to 3PhPy has been attributed to a possible through-space interaction of n - and π-electronic clouds. A discernible feature for phenyl pyridines is the increased basicity and polarity in the excited singlet state. The internal conversion seemed to be active in both phenyl pyridines and bipyridines in MCH solvent and for bipyridines in ethanolic solution, the second-order spin-orbit coupling comes into picture.

Photo-rotamerism of 2,2′-pyridil in different environments: A quest for geometry in excited states

Abstract Temperature and solvent (polarity) dependent photorotamerism in 2,2′-pyridil (P) has been observed from photoluminescence studies. Dual fluorescence and phosphorescence of P also substantiate the idea of the presence of different rotamers. The changes in intensities and positions of the two fluorescence peaks of P in aqueous β-cyclodextrin (β-CD) solution are due to the impediment in intramolecular rotation and the stifling of the radiationless process caused by partial inclusion in the β-CD cavity. At high concentration, the T ← S0 transition could be observed at 300 K. Two close-lying, strongly coupled 3π, π∗ (T2) and 3n, π∗ (T1) states of P eventuate in bi-exponential triplet decay. Protonation is favoured at the site of nitrogen.

Weak electronic transition in 1,2,3-trimethoxy benzene

Abstract The paper reports the weak absorption system of 1,2,3-trimethoxy benzene near 2750 A, measured in the solid phase and in an isobutyl alcohol rigid glass at 77 K. The rigid glass spectrum shows a purely electronic part and a weaker vibrationally induced part in which the perturbing vibration is totally symmetrical. In the solid phase, the pure electronic bands split into two components of equal intensity. The vibronic bands do not show any splitting; there is only an enhancement in the intensity of the bands.

Some characteristic features of the electronic absorption spectra of 1,3,5-trimethoxy benzene in the solid phase and in rigid glass media at 77 K

Abstract The near ultraviolet absorption system of 1,3,5-trimethoxy benzene in the solid phase and in an isobutyl alcohol rigid glass at 77 K is characterised by the appearance of the 0,0 band and excitation of totally symmetric vibrations. In the spectrum of the solid, two out-of-plane vibrations are coupled with the electronic transition. The spectral features indicate that in the solid phase, the molecular symmetry is lower than D 3h and the molecule is probably not planar.

Steady state spectral characteristics of 1-phenyl-3-pyrazolidinone in different environments

Abstract Analysis of steady state absorption spectra of 1-phenyl-3-pyrazolidinone (PPd) in different organic solvents at ambient temperature shows that it is strongly polarity dependent which is associated with intramolecular charge transfer. A correlation is shown between the appearance of dual fluorescence of PPd in alcoholic solutions at 300 K and the formation of hydrogen bonded solute-solvent complexes. Evolution of a new band at the red end of the absorption spectra of PPd in all the solvents with traces of water impurities and the fluorescence study in aqueous β-cyclodextrin solutions establish beyond doubt that a PPd molecule has a high affinity to water molecules. Phosphorescence spectra are also recorded in methyl cyclohexane and ethanol matrices at 77 K.

Electronic spectra of paramethoxy benzyl alcohol and parachloro benzyl cyanide

The electronic absorption spectra of paramethoxy benzyl alcohol (pmba) and parachloro benzyl cyanide (pcbc) are described. The broad features of the spectra of the molecules are consistent with allowed transition forC2v symmetry. However, the solid state and glass matrix spectra of pmba at 77K indicate possible deviation from planarity in the structure of the molecule. In pcbc, it is pointed out that intensity borrowing may be responsible for the large intensity of the vibrationally-induced part of the spectra, in which non-totally symmetric vibrations are excited.

Electronic Spectrum of Tetralin

Abstract Vibrational structure and intensity of the electronic absorption spectrum of tetralin vapour are reported. It is pointed out that the molecule is probably strained and consideration of G-π conjugation may be important in explaining the spectral features.