Spectrochimica Acta Part A 71 (2008) 1327–1332 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Spectroscopic investigation of 3-pyrazolyl 2-pyrazoline derivative in homogeneous solvents Smritimoy Pramanik, Paltu Banerjee, Arindam Sarkar, Attreyee Mukherjee, Kumar K. Mahalanabis ∗ , Subhash Chandra Bhattacharya ∗ Department of Chemistry, Jadavpur University, Kolkata 700032, India article info Article history: Received 11 January 2008 Received in revised form 25 March 2008 Accepted 14 April 2008 Keywords: Fluorescence Relaxation dynamics Solvent polarity Hydrogen bonding abstract How solvent conditions such as solvent polarity and hydrogen-bonding affect the fluorescence of a newly synthesized 3-pyrazolyl 2-pyrazoline derivative (Pyz) having pharmaceutical activity has been explored. The solvatochromic effect of Pyz is due to a change in dipole moment of the compound in the excited state. The relaxation of S 1 state is perturbed in hydrogen-bonding solvents. The fluorescence properties of the systems are strongly dependent on the polarity of the media. The non-radiative relaxation process is facilitated by an increase in the polarity of the media. The photophysical response of Pyz in different solvents has been explained considering solute–solvent interactions. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Photophysical study of pyrazoline derivatives in homogeneous solvents originates principally from two aspects—the first one stems from its novel biological applications in pharmaceuticals and the second one arises due to presence of electron donors and acceptors at N(1) and C(3) positions, respectively. 2-Pyrazoline derivatives have been effectively utilized as antibacterial, antifun- gal, antiviral, antiparasitic, antitubercular and insecticidal agents [1–3] and as a hole-conveying medium in photoconductive mate- rials and electroluminescence devices [4,5]. Pyrazoline derivatives are well known fluorescent compounds with high quantum yields and are used as optical brightening agents for textiles, fabrics, plas- tics and papers [6]. These compounds have been utilized as fluo- rescent probes in some chemosensors [7]. 2-Pyrazoline derivatives are considered to be an important organic heterocyclic “transition” material, i.e. a material which shares many properties with con- ventional semiconductors and insulators like organic molecular crystals [8]. Ranging from tens to hundreds of nanometers, recently different groups prepared pyrazoline nanoparticles by using the reprecipitation method and explored their size-tunable optical properties for the application in optoelectronic device [6,9–11]. Fluorescent probes are powerful tools in cell biology for the non- invasive measurement of intracellular ion concentrations and to ∗ Corresponding author. Tel.: +91 33 2414 6223; fax: +91 33 24146584. E-mail addresses: sbjuchem@yahoo.com, scbhattacharyya@chemistry.jdvu.ac.in (S.C. Bhattacharya). visualize labile zinc and iron pools, or as pH sensors [12–15]. For the design of cation specific fluorescent probes, a synthetically more flexible fluorophore structure would be desirable. Among possible substitutes, pyrazoline-based fluorophores stand out due to their simple structure and favorable photophysical properties such as large extinction coefficient and quantum yields (0.6–0.8) [16,17]. Variation of photophysical process of 2-pyrazoline derivatives are observed depending on the substituent [18–20]. In our earlier work on pyrazoline derivatives having fused norborane ring present at 3a and 7a carbon of 2-pyrazoline ring fluorescence emissions from S 2 state have been observed [21]. In this study, photophysical properties of another derivative of 2-pyrazoline (Pyz) in homogeneous solvents have been studied. The compound, ethyl 1-(4-bromophenyl)-3-(4 cyano-3-methyl- 1phenyl-1H-pyrazole-5yl)-4,5, dihydro-1H-pyrazole-5-carboxy- late (Scheme 1) has phenyl group at N(1) position of pyrazoline with methyl and cyano substitution at C(3) and C(4) position of pyrazole, respectively. Generally, phenyl substitution at N(1) position of pyrazoline ring makes it highly fluorescent and simul- taneously extended conjugation from 2-pyrazoline to pyrazole ring enhances the fluorescence intensity of the compound. In this compound, the ethyl carboxylate group is substituted in C(5) position of pyrazoline ring. Our target is to study the solvent dependent radiative transitions and relaxation dynamics of this derivative of pyrazole substituted 2-pyrazoline from the excited singlet state. The results obtained from the steady state and time- resolved fluorescence studies have been rationalized considering solute–solvent interaction. A comparative study of the kinetics of the probe in different solvents has been made. 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.04.011