The chairman of the Indianapolis Symphony Orchestra insists he knows of no specific reason behind the abrupt departure of CEO Simon Crookall after seven years.

In an interview Friday morning, board chairman John Thornburgh noted that the ISO’s former chief executive, Richard Hoffert, held the post for six years, and that seven years is a long tenure for such a demanding job.

“The only thing I’m aware of is he wanted to pursue some other opportunities,” he said of Crookall.

Crookall’s departure was announced Thursday evening and was effective immediately. He doesn’t appear to have a new job lined up, as he did not indicate where he’s headed next. He did not return a message left at his home.

The timing of the decision seemed surprising, given that the ISO is in the midst of a $100 million capital campaign. It’s also enjoying the national spotlight as host of “Late Night with Jimmy Fallon” at Hilbert Circle Theatre during Super Bowl festivities.

“In terms of the immediacy of the decision, that was a function of what Simon wanted to do,” Thornburgh said. “He has agreed to provide transition assistance.”

Finance vice president Jackie Groth will be interim CEO. Thornburgh said he expects the search to last at least six months, and hopes to find someone within a year.

Crookall, 51, has weathered controversy and financial pressure. He ousted former music director Mario Venzago in 2009 and brought in a new, young music director, Krzysztof Urbanski, in 2010.

The symphony struggled with operating losses following the 2008 financial crisis. At the ISO's annual meeting in November, Crookall said that with cost-cutting and increased fundraising, the ISO should have a balanced budget by the conclusion of the fiscal year ending Aug. 31, 2014.

The ISO's expenses of $25.6 million exceeded revenue by $1.7 million for the 2011 fiscal year. Last year's deficit was $1 million less than the previous year's and $1.1 million less than than the deficit two years ago.

A musicians’ representative said Crookall’s departure comes amid a larger shakeup in the management ranks. “They’re going through restructuring on the management side right now,” said Richard Graef, chairman of the orchestra committee. “It hasn’t just been Simon.”

In the past few weeks, the ISO has also parted ways with Martin Sher, vice president of artistic planning.

Graef said the departure came around the same time that the orchestra announced a new management structure with three vice presidents instead of six.

Thornburgh said the restructuring of the vice presidents' ranks was Crookall's decision. He expected Groth to assemble her own management team.

United Kingdom-based cultural commentator Norman Lebrecht speculated in a blog post that Music Director Krzysztof Urbanski played a role in Crookall’s departure. Citing anonymous sources, Lebrecht said Urbanski had objected to Sher’s firing.

Urbanski’s representative directed questions back to Thornburgh. “Krzysztof never publicly comments on issues related to orchestra administration,” said Jennifer Spencer, director at London-based HarrisonParrott in an e-mail.

Thornburgh said he wasn’t aware of Urbanski influencing Crookall’s decision to leave.

Musicians were not unhappy with Crookall, Graef said. “We respect what he’s done for the orchestra,” he said. “He’s given 150 percent, always.”

Crookall seemed to have at least a working relationship with the musicians. They agreed to a 12-percent pay cut in their last three-year contract, struck in October 2009, saving the ISO $4 million.

At the same time, Crookall took a 15-percent pay cut, and vice presidents took a 10-percent cut. Crookall was paid a base salary of $229,847 in the 2010 fiscal year with total compensation of $265,262.

The one blemish on Crookall’s record is failing to land significant donations, Graef said, although he added that the musicians don’t lay the blame with him. “It’s a very hard job.”

The capital campaign is overseen by vice president for development Sean Dunlavy, who shifted all his work to that project early in the year, Thornburgh said.