Twisted Intramolecular Charge Transfer of 2-(4‘-N,N-Dimethylaminophenyl)pyrido[3,4-d]imidazole in Cyclodextrins:  Effect of pH

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2000-03, Vol.104 (12), p.2542-2551
• Main Authors: Krishnamoorthy, G, Dogra, S. K
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp992792t

Absorption, fluorescence, and fluorescence excitation spectra of 2-(4‘-N,N-dimethylaminophenyl)pyrido[3,4-d]imidazole (DMAPPI) have been studied as a function of cyclodextrins (CDxs) and acid concentrations. The above study has revealed that a −NMe2 group enters into the CDx cavity and a pyridoimidazole (PI) ring is present at the interface. The N3− atom and >NH group of the PI ring are involved in the hydrogen bonding with the water molecule present at the interface and/or with the hydroxyl groups of the CDxs, and the N6− atom is involved in hydrogen bonding with the bulk water. Two monocations (MC1 and MC3) are present in the S0 state, and MC2 and MC3 are present in the S1 state. MC2 emission is observed when MC1 is excited to the S1 state and involves biporotonic phototautomerism, whereas for the MC3 the emission is not observed from the locally excited state, but observed from the twisted intramolecular charge transfer (TICT) state. Fluorescence band maxima of all the bands are blue shifted and their fluorescence quantum yields are enhanced when DMAPPI is encapsulated in the CDxs cavity. The enhancement and the relative blue shifts observed in the band maxima of the TICT band are larger than those of the normal band.