Appl Phys B (2011) 103:917–924 DOI 10.1007/s00340-010-4287-0 High efficiency dye laser with low fluorescence yield pyrromethene dyes: experimental and theoretical studies K.K. Jagtap · D.K. Maity · A.K. Ray · K. Dasgupta · S.K. Ghosh Received: 4 September 2010 / Revised version: 24 September 2010 / Published online: 6 November 2010 © Springer-Verlag 2010 Abstract A combined experimental and theoretical study of the photo-physical, laser properties and molecular struc- tures of three relatively recent Pyrromethene (PM) class dyes, PM597, PM580 and PM567, have been carried out. Laser characteristics of these three PM dyes were compared with three other widely used Rhodamine (RH) class dyes, RH6G, RHB and KRS, using a narrow-band dye laser setup, transversely pumped by the second harmonic (532 nm) of a Q-switched Nd-YAG laser. In addition to generating com- parative data of these dyes for optimal use in dye lasers, we observed that unlike the RH dyes, the PM dyes show high efficiencies and wide tunability, despite the low fluo- rescence yield and high rate of non-radiative decay. Partic- ularly, PM597 dye, in spite of a very low quantum yield of fluorescence ( = 0.42), high non-radiative decay rate, and a large distortion from planarity in its excited state, when used in a laser cavity it exhibited similar laser efficiency and a beneficially wider tuning curve in comparison to other two PM dyes. Theoretical studies were carried out applying den- sity functional theory and time-dependent density functional theory (DFT/TDDFT) to obtain new information on ground and the first excited state geometrical parameters of the PM K.K. Jagtap · A.K. Ray ( ) · K. Dasgupta Laser & Plasma Technology Division, Bhabha Atomic Research Centre, Mumbai 400085, India e-mail: alokray@barc.gov.in K.K. Jagtap Chemistry Dept., Univ. of Pune, Pune 411007, India D.K. Maity · S.K. Ghosh Theoretical Chemistry Section Bhabha Atomic Research Centre, Mumbai 400085, India D.K. Maity e-mail: dkmaity@barc.gov.in dyes. Good correlation between calculated molecular prop- erties and experimental results was observed for the evolu- tion of the longest wavelength absorption maximum. 1 Introduction Several chromophores of highly fluorescent organic com- pounds are now known, but the dipyrromethene BF 2 (PM or BODIPY) family of dyes has attracted interest over the past decade as being one of the more versatile fluorophores due to its applications as biomolecular labels [1], novel or- ganic materials [2], fluorescent chemo-sensors [3], and ac- tive media in liquid [4] and solid-state [5] dye lasers, among others. The use of PMs as effective biological label has been complemented by their preference to function as an efficient laser dye. The general observation of good laser efficiency of PM dyes in solid-state as well as in liquid dye lasers has led to several investigations [6–8] on its photo-physical and laser properties. In parallel, more fundamental studies on the chemical reactivity and photo-degradation mechanism of the new PM dyes emerged. However, the rapid rate of photo-degradation of PM dyes in air-equilibrated liquid so- lutions, [9, 10] due to its self-sensitized photo-oxidation by reacting with generated singlet oxygen, remained a cause of primary concern for use in liquid dye lasers, especially in high-average power dye lasers. Remarkable improvement in the photo-stability of PM567 dye solutions, while deployed in low [9] as well as in high-repetition rate dye lasers [10], was observed with addition of 1,4-diazabicyclo [2,2,2] oc- tane (DABCO), a singlet oxygen quencher. There have also been efforts [8, 12–14] to synthesize various analogues of PM dyes possessing better photo-stability as well as higher efficiency for dye laser and other applications.