Ultrafast excited state dynamics of 1-nitropyrene: Effect of H-bonding

作者：Mora Aruna K; Murudkar Sushant; Singh Prabhat K; Gowthaman N S K; Mukherjee Tulsi; Nath Sukhendu^*

来源：Journal of Photochemistry and Photobiology A: Chemistry , 2013, 271: 24-30.

DOI：10.1016/j.jphotochem.2013.08.003

• 1-Nitropyrene
• Ultrafast dynamics
• Fluorescence
• H-bonding

Ultrafast excited state dynamics of 1-nitropyrene has been carried out using femtosecond fluorescence upconversion technique. Detailed time-resolved emission measurements were performed in protic and aprotic solvents of similar polarity. It is seen that although the singlet-triplet energy gap in polar solvents is quite large, the excited state decay shows intersystem crossing in sub-picosecond time scale as observed for nonpolar solvents with isoenergetic singlet and triplet state. The appearance of the sub-picosecond decay component in polar solvents has been explained on the basis of the dynamical nature of the solvent relaxation process. Further, the contribution of the sub-picosecond decay component is much more for the solvent with slower solvent relaxation time. Time-resolved area normalized emission spectra (TRANES) show the presence of two emissive species for 1-nitropyrene in aprotic solvent while only one emissive species has been observed in protic solvent. The additional emissive species in aprotic solvent has been assigned to the structurally relaxed excited singlet state formed due to the rotation of the nitro group around the pyrene moiety. However, such rotation of the nitro group is prevented in protic solvent due to the formation of H-bonded complex between the solute and the solvent. Formation of H-bonding between protic solvent and nitropyrene is also confirmed by quantum chemical calculations.

• 出版日期2013-11-1